REFERENCE

Proteinase Research Glossary

Reference definitions for the core terms used in proteinase research — enzyme mechanism classes, MMP/cathepsin/ADAM families, activity assay techniques, antibody validation, and recombinant protein production.

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General Protease Biology

Protease: Any enzyme that catalyzes the hydrolysis of peptide bonds in proteins or peptides. Proteases (EC 3.4) are subdivided by catalytic mechanism (serine, cysteine, aspartic, metallo, threonine) and by cleavage position (endo- vs. exopeptidase). Also called proteinase or peptidase depending on substrate size and cleavage mode. See more →
Proteinase: A protease that acts preferentially on intact, folded proteins rather than short peptides, cleaving internal peptide bonds (endopeptidase activity, EC 3.4.21–24 and 3.4.99). The term is used interchangeably with protease in most literature; TPB's catalog focuses specifically on proteinases and their endogenous inhibitors. See more →
Endopeptidase: A peptidase (EC 3.4.21–24, 3.4.99) that cleaves peptide bonds within the interior of a polypeptide chain, away from the N- or C-terminus. Examples include trypsin (EC 3.4.21.4), MMP-9 (EC 3.4.24.35), and caspase-3 (EC 3.4.22.56). Distinct from exopeptidases, which act at chain termini. See more →
Exopeptidase: A peptidase (EC 3.4.11–19) that hydrolyzes peptide bonds at or near the N-terminus (aminopeptidase) or C-terminus (carboxypeptidase) of a polypeptide. Exopeptidases are critical in antigen processing, protein maturation, and dietary protein digestion.
Carboxypeptidase: An exopeptidase (EC 3.4.16–18) that sequentially removes amino acid residues from the free C-terminus of a polypeptide. Mechanistic classes include serine carboxypeptidases (EC 3.4.16), metallocarboxypeptidases (EC 3.4.17), and cysteine carboxypeptidases (EC 3.4.18). Carboxypeptidase A (EC 3.4.17.1) is a classical metalloenzyme example.
Aminopeptidase: An exopeptidase (EC 3.4.11) that cleaves single amino acid residues from the free N-terminus of a peptide or protein. Most are zinc-dependent metalloenzymes. Aminopeptidase N (CD13, EC 3.4.11.2) is expressed on tumor vasculature and is a studied oncology target.
Hydrolase: An enzyme of class EC 3 that catalyzes the cleavage of chemical bonds by the addition of water. Proteases are a subclass of hydrolases acting on peptide (amide) bonds (EC 3.4). Hydrolases also include nucleases, lipases, and glycosidases, all sharing the same fundamental water-addition mechanism.
Catalytic triad: A set of three spatially conserved active-site residues—classically Ser-His-Asp in serine proteases (e.g., trypsin, chymotrypsin)—that cooperate to hydrolyze peptide bonds via a charge-relay system. Analogous triads (Cys-His-Asp/Asn) occur in cysteine proteases such as the caspases and cathepsins.
Active site: The three-dimensional region of an enzyme that directly binds substrate and catalytic cofactors, forming the microenvironment for the chemical reaction. In proteases, the active site contains the catalytic residues (e.g., the triad) and a series of substrate-binding subsites (S1–Sn, S1'–Sn') as defined by Schechter and Berger (1967).
Zymogen: An inactive enzyme precursor requiring proteolytic cleavage of an inhibitory prodomain for activation. Zymogens ensure spatiotemporal control of protease activity; examples include pepsinogen (→ pepsin), trypsinogen (→ trypsin), and the pro-MMPs (→ active MMPs). Activation can occur auto- or trans-catalytically. See TPB's guide for zymogen activation assay design. See more →
Proenzyme: Synonym for zymogen; an enzymatically inactive precursor protein that requires post-translational modification—most commonly proteolytic removal of an N-terminal prodomain—to generate the catalytically competent mature form. The term is used interchangeably with zymogen throughout the literature and in TPB catalog annotations. See more →
Pro-form: The full-length, unprocessed translation product of a protease gene, retaining the inhibitory prodomain. The pro-form is distinct from the signal-peptide-containing preproprotein; it represents the secreted or intracellular precursor immediately prior to activation. Antibodies raised against the prodomain can distinguish pro-form from mature enzyme on Western blot. See more →
Prodomain: The N-terminal regulatory extension of a zymogen that occludes the active site and maintains latency. In MMPs, the prodomain contains a conserved cysteine-switch motif (PRCGXPD) that coordinates the catalytic zinc. Prodomain removal—by autocatalytic or trans-proteolytic cleavage—is the defining activation step. See more →
Mature enzyme: The fully processed, catalytically active form of a protease after removal of signal peptide, prodomain, and any other inhibitory segments. Molecular weight of the mature form is lower than the pro-form; size differences are detectable by Western blot and are a standard indicator of in-vivo activation state. See more →
Autocatalytic activation: A mode of zymogen activation in which the protease cleaves its own prodomain, either intramolecularly (cis) or through bimolecular interaction between two pro-enzyme molecules (trans-autocatalysis). Pepsin and several caspases exhibit pH- or concentration-dependent autocatalytic activation. Distinguishable from trans-activation by inhibitor-titration kinetics. See more →
Trans-activation: Zymogen activation in which a separate, distinct protease cleaves the prodomain to generate the active enzyme. For example, membrane-type MMPs (MT-MMPs) trans-activate pro-MMP-2 on the cell surface. Trans-activation often provides physiological amplification and is a key regulatory checkpoint in protease cascades. See more →
Limited proteolysis: Highly selective, single- or few-site cleavage of a protein substrate that modifies function without complete degradation. Examples include signal peptide removal, hormone maturation (proinsulin → insulin), and zymogen activation. Limited proteolysis contrasts with processive degradation and is a fundamental mechanism of irreversible post-translational regulation.
Substrate specificity: The biochemical selectivity of a protease for particular amino acid sequences or structural features flanking the scissile bond. Determined by the geometry of the substrate-binding subsites (S1–Sn). Profiled experimentally with positional scanning synthetic combinatorial libraries (PS-SCL) or fluorogenic peptide panels. See TPB's fluorogenic substrate guide for assay-design guidance. See more →
Substrate cleavage: The hydrolysis of a specific peptide bond within a substrate protein or peptide, producing two fragments (the 'prime-side' and 'non-prime-side' products). Cleavage is characterized by the cleavage site sequence, monitored by SDS-PAGE, HPLC, or fluorescence if a labeled substrate is used. See /guides/protease-activity-assays for assay-design guidance. See more →
Peptide bond hydrolysis: The chemical reaction in which a water molecule is added across the amide (–CO–NH–) bond linking two amino acid residues, yielding a free carboxyl terminus and a free amino terminus. This is the universal reaction catalyzed by all proteases; the reaction is thermodynamically favorable but kinetically slow without enzymatic catalysis (half-life ~500 years at pH 7, 25 °C).
Allosteric inhibition: Reduction of enzyme activity through ligand binding at a site topographically distinct from the active site, inducing conformational changes that reduce catalytic efficiency (kcat), substrate affinity (Km), or both. Some MMP inhibitors and ADAM inhibitors exploit allosteric mechanisms to achieve selectivity not achievable by active-site-directed compounds.
Proteolysis: The enzymatic degradation or processing of proteins by proteases through peptide bond hydrolysis. Proteolysis ranges from complete polypeptide degradation (as in the ubiquitin-proteasome pathway) to precise limited cleavages governing signaling, ECM remodeling, and zymogen activation. Dysregulated proteolysis is implicated in cancer, fibrosis, and neurodegeneration.
Proteolytic processing: Regulated, limited proteolysis that converts a precursor protein into a functionally distinct mature form. Encompasses signal-peptide cleavage, prodomain removal, propeptide maturation, and ectodomain shedding. Unlike nonspecific degradation, proteolytic processing is precise in site and timing, and is often irreversible. See more →
Cleavage site: The specific peptide bond within a substrate that a protease hydrolyzes, defined by the flanking amino acid sequence context. Described using Schechter and Berger subsite notation (P3–P2–P1↓P1'–P2'–P3'), where ↓ marks the scissile bond. Cleavage-site databases such as MEROPS and CutDB catalog experimentally validated sites.
Scissile bond: The specific peptide (amide) bond within a substrate that undergoes hydrolysis during a protease reaction. In Schechter and Berger notation it lies between the P1 and P1' residues. Structural studies locate the scissile bond directly within the protease active site, coordinated by catalytic residues and the oxyanion hole.
Subsite nomenclature (P1-P1'): A standardized framework for describing substrate–protease interactions, introduced by Schechter and Berger (1967). Substrate residues N-terminal to the scissile bond are designated P1, P2, P3… (non-prime side); residues C-terminal are P1', P2', P3'… (prime side). Complementary enzyme subsites are S1, S2… and S1', S2'…. Widely used in inhibitor design and specificity profiling. See more →
Schechter and Berger notation: The subsite numbering convention for substrate–protease interactions published by Israel Schechter and Arieh Berger in BBRC (1967). Substrate residues are numbered P1–Pn (non-prime, toward N-terminus) and P1'–Pn' (prime, toward C-terminus) relative to the scissile bond; corresponding enzyme pockets are S1–Sn and S1'–Sn'. Now universal in protease literature and inhibitor design. See more →

Enzyme Mechanism Classes

Aspartic protease: A protease that uses two conserved aspartate residues in the active site to activate a water molecule for nucleophilic attack on the peptide bond. Members include pepsin (A1 family), cathepsin D, and HIV-1 protease. Optimal activity typically occurs at acidic pH. Inhibited by pepstatin A. EC 3.4.23. See more →
Cysteine protease: A protease that employs a catalytic dyad or triad in which a cysteine thiol acts as the nucleophile, typically assisted by a histidine base. Families include calpains (C2), cathepsins B/L/S (C1), and caspases (C14). EC 3.4.22. Sensitive to iodoacetamide and E-64. TPB catalogs antibodies and recombinant proteins for multiple cysteine protease targets. See more →
Serine protease: A protease using a Ser-His-Asp catalytic triad (or Ser-Lys dyad in signal peptidases) in which serine acts as the nucleophile. Largest mechanistic class; includes trypsin (S1), subtilisin (S8), and elastase. EC 3.4.21. Inhibited by PMSF and DFP. TPB catalogs antibodies and recombinant proteins for multiple serine protease targets. See more →
Metalloprotease: A protease that coordinates a divalent metal ion — most commonly zinc — to polarize a water molecule for peptide bond hydrolysis. Includes the matrix metalloproteinase (MMP) family, ADAM/ADAMTS proteases, and thermolysin. EC 3.4.24. Inhibited by EDTA and 1,10-phenanthroline. TPB has cataloged metalloprotease antibodies and recombinants since 1994. See more →
Threonine protease: A protease that uses the hydroxyl of an N-terminal threonine residue as the catalytic nucleophile, with the free α-amino group serving as the base. Characteristic of the proteasome (T1 family) and ornithine acetyltransferases. EC 3.4.25.1 (proteasome endopeptidase complex). Self-processing autocatalysis is required for active-site exposure.
Glutamic protease: A protease class in which a glutamate and glutamine (or glutamate pair) constitute the catalytic dyad, activating a water molecule for hydrolysis without a nucleophilic amino acid directly attacking the substrate. Exemplified by scytalidoglutamic peptidase (G1 family, MEROPS clan GX). Rare in mammals; more prevalent in filamentous fungi.
Asparagine peptide lyase: A protease that cleaves peptide bonds via an elimination mechanism rather than hydrolysis, using the side-chain amide of asparagine as the catalytic nucleophile. Classified EC 4.3.2 (lyases), not EC 3.4. Found in self-splicing inteins and certain viral capsid maturation proteases. Uniquely, reaction requires no water molecule.
MEROPS database: A curated, hierarchical reference database (Rawlings et al., Nucleic Acids Res.) that classifies peptidases and their inhibitors into clans, families, and individual entries based on sequence homology and catalytic mechanism. Maintained at the Wellcome Sanger Institute. Widely used as the authoritative nomenclature source for protease gene and protein annotation.
Clan: In MEROPS nomenclature, a clan is the highest hierarchical grouping of protease families that share a common evolutionary origin, evidenced by statistically significant structural or sequence similarity around the active site. Clans are designated by two-letter codes (e.g., PA for chymotrypsin-like serine/cysteine proteases, MA for metzincin metalloproteases).
Family: In MEROPS nomenclature, a family groups proteases with statistically significant amino acid sequence similarity to a type example, independent of substrate specificity. Designated by a letter indicating catalytic type (S, C, A, M, T, G, N, U) followed by a number (e.g., M10 for the MMP family, C1 for papain-like cysteine proteases). Families are nested within clans.
EC number: Enzyme Commission number — a four-level numerical classification (e.g., EC 3.4.21.4 for trypsin) assigned by the IUBMB to define enzyme reaction type, substrate class, bond specificity, and individual activity. The first digit denotes reaction class (EC 3 = hydrolases). EC numbers are species-independent and reaction-centric, not structural.
EC 3.4 (peptidases): The IUBMB sub-subclass covering all enzymes that hydrolyze peptide bonds (proteases/peptidases). Subdivided by catalytic mechanism: EC 3.4.11–19 (exopeptidases) and EC 3.4.21–25 (endopeptidases by mechanism: serine, cysteine, aspartic, metallopeptidase, threonine). Note: asparagine peptide lyases are reclassified to EC 4.3.2. The complete human degradome contains ~600 EC 3.4 members.

Matrix Metalloproteinases (MMPs)

MMP (Matrix Metalloproteinase): A family of zinc-dependent endopeptidases (EC 3.4.24.–) that collectively degrade most ECM components. Over 23 human MMPs share a conserved catalytic domain with the HEXXHXXGXXH zinc-binding motif. Activity is tightly regulated by TIMPs, furin-like proprotein convertases, and autocatalytic mechanisms. TPB catalogs matched antibodies and recombinants for multiple MMP family members. See more →
Gelatinase A (MMP-2): A 72 kDa type IV collagenase (EC 3.4.24.24; UniProt P08253) that degrades denatured collagens (gelatins), collagen IV, V, and X. Distinguished by three fibronectin type II repeats within its catalytic domain. Activated at the cell surface via a MT1-MMP/TIMP-2 ternary complex. TPB catalogs a matched antibody and recombinant for this target. See more →
Gelatinase B (MMP-9): A 92 kDa gelatinase (EC 3.4.24.35; UniProt P14780) that cleaves denatured collagens, collagen IV, V, and XIV, as well as aggrecan. Contains three fibronectin type II inserts and a unique type V collagen-like domain. Widely implicated in tumor invasion, neuroinflammation, and angiogenesis. TPB catalogs a matched antibody and recombinant for this target. See more →
Interstitial Collagenase (MMP-1): The archetypal MMP (EC 3.4.24.7; UniProt P03956), cleaving fibrillar collagens I, II, and III at a single Gly-Ile/Leu bond three-quarters from the N-terminus. Secreted as a ~52 kDa zymogen; activated extracellularly by MMP-3 and plasmin. Primary mediator of connective-tissue turnover in fibrosis and arthritis models. TPB catalogs a matched antibody and recombinant for this target. See more →
Stromelysin-1 (MMP-3): A broad-spectrum stromelysin (EC 3.4.24.17; UniProt P08254) that degrades fibronectin, laminin, proteoglycans, and collagen IV, and activates several pro-MMPs including MMP-1 and MMP-9. Secreted as a ~54 kDa zymogen. Elevated in rheumatoid synovium and breast carcinoma stroma. TPB catalogs a matched antibody and recombinant for this target. See more →
Collagenase-3 (MMP-13): A collagenase (EC 3.4.24.–; UniProt P45452) with the broadest fibrillar collagen specificity among MMPs, preferentially cleaving collagen II but also I, III, and X. Key mediator of cartilage destruction in osteoarthritis and endochondral ossification. Activated by MT1-MMP and MMP-2. TPB catalogs a matched antibody and recombinant for this target. See more →
MT-MMP (Membrane-Type MMP): A subfamily of six MMPs (MT1–MT6; MMP-14, -15, -16, -17, -24, -25) anchored to the cell surface via a transmembrane domain (MT1–3, MT5) or GPI linkage (MT4, MT6). MT1-MMP (MMP-14; UniProt P50281) is the best-characterized, activating pro-MMP-2 on the plasma membrane and directly cleaving collagen I. TPB catalogs matched antibodies and recombinants for MT1-MMP. See more →
Hemopexin Domain: A ~200-residue C-terminal domain present in most MMPs, adopting a four-bladed β-propeller fold stabilized by a calcium ion and a single disulfide bridge. Mediates substrate recognition, TIMP binding, and MMP dimerization. Deletion of this domain sharply reduces collagenolytic activity, demonstrating its role beyond simple anchoring. See more →
Fibronectin Type II Domain: Collagen/gelatin-binding inserts (~60 residues each) found in three tandem copies within the catalytic domains of MMP-2 and MMP-9. Structurally homologous to fibronectin modules, they confer high-affinity binding to denatured collagen and gelatins, directing these gelatinases to their substrates prior to catalysis. See more →
APMA Activation: Treatment of pro-MMPs with 4-aminophenylmercuric acetate (APMA, typically 1–2 mM) to generate catalytically active enzyme in vitro. APMA disrupts the cysteine switch interaction, triggering autolytic removal of the prodomain. Commonly used before fluorogenic substrate or zymography assays. See /guides/protease-activity-assays for assay-design guidance. See more →
MMP Propeptide: An N-terminal ~80-residue domain present in all MMP zymogens that maintains latency by coordinating the catalytic zinc via a conserved cysteine residue (the cysteine switch). Proteolytic or chemical removal of the propeptide—by convertases, other MMPs, or APMA—exposes the active site and initiates catalysis. See /guides/zymogens-and-proenzymes. See more →
Cysteine Switch: The latency mechanism of MMP zymogens, first described by Van Wart & Birkedal-Hansen (1990). A conserved PRCGXPD motif in the propeptide positions a cysteine thiol to coordinate the catalytic zinc, blocking water access and preventing substrate hydrolysis. Perturbation by chaotropes, oxidants, or APMA triggers autolytic activation. See more →
ECM Remodeling: The coordinated degradation, deposition, and structural reorganization of extracellular matrix components—collagens, fibronectin, laminins, proteoglycans—mediated primarily by MMPs, ADAMs, and serine proteases. Physiologically essential for morphogenesis, wound healing, and angiogenesis; dysregulated ECM remodeling underlies fibrosis, cancer invasion, and inflammatory tissue destruction. See more →
TIMP (Tissue Inhibitor of Metalloproteinases): A family of four endogenous MMP inhibitors (TIMP-1–4) that bind the MMP active site in a 1:1 stoichiometric, reversible manner (Ki ~picomolar). The N-terminal domain contacts the zinc; the C-terminal domain engages the hemopexin domain. TIMPs regulate ECM homeostasis and serve as independent signaling molecules in some contexts. See more →
TIMP-1: A 28.5 kDa secreted glycoprotein (UniProt P01033) that preferentially inhibits MMP-1, -2, -3, -7, -8, -9, -10, and -11 but poorly inhibits MT-MMPs. Forms a high-affinity complex with pro-MMP-9 that blocks activation. Elevated TIMP-1 is associated with poor prognosis in several carcinomas. TPB catalogs a matched antibody and recombinant for this target. See more →
TIMP-2: A 21 kDa non-glycosylated secreted protein (UniProt P16035) with dual roles: at low concentrations it bridges pro-MMP-2 to MT1-MMP on the cell surface to facilitate MMP-2 activation; at higher concentrations it inhibits MT1-MMP and most MMPs. Unique among TIMPs in its requirement for MT1-MMP-mediated MMP-2 activation. TPB catalogs a matched antibody and recombinant for this target. See more →
TIMP-3: A 24 kDa ECM-bound TIMP (UniProt P35625) that, unlike TIMP-1/2, is sequestered in the pericellular matrix via heparan sulfate binding. Inhibits MMPs as well as ADAM-10, -12, -17 (TACE), and ADAM-TS4. Loss-of-function mutations cause Sorsby fundus dystrophy. TPB catalogs a matched antibody and recombinant for this target. See more →
TIMP-4: The most recently identified TIMP (UniProt Q99727), with preferential expression in heart, brain, and adipose tissue. Inhibits MMP-1, -2, -3, -7, and -26, and forms a high-affinity complex with pro-MMP-2 similar to TIMP-2. Its tissue-restricted expression pattern distinguishes it functionally from the ubiquitously expressed TIMP-1 and TIMP-2. TPB catalogs a matched antibody and recombinant for this target. See more →

ADAM and ADAMTS Family

ADAM (a disintegrin and metalloprotease): A family of zinc-dependent transmembrane endopeptidases (clan MA, family M12B) characterized by a prodomain, metalloprotease, disintegrin-like, cysteine-rich, and EGF-like domain architecture. ADAMs mediate ectodomain shedding of growth factors, cytokines, and receptors, and participate in cell adhesion, signaling, and fertilization. Over 20 human members are known; ~12 are proteolytically active. See more →
ADAM10: A transmembrane ADAM family sheddase (EC 3.4.24.81; UniProt O14672) that cleaves Notch, E-cadherin, N-cadherin, ephrin-A2, and amyloid precursor protein (APP). Functions as the principal alpha-secretase for APP in neurons. Activated by pro-protein convertases removing its ~10 kDa prodomain. TPB catalogs a matched antibody + recombinant for this target. See more →
ADAM17 (TACE): Tumor necrosis factor-alpha converting enzyme (TACE; EC 3.4.24.86; UniProt P78536); the primary sheddase responsible for TNF-α ectodomain release and a major regulator of EGFR-ligand (EGF, TGF-α, amphiregulin) shedding. Activated intracellularly by furin-family convertases. Implicated in inflammation, cancer, and cardiac hypertrophy. TPB catalogs a matched antibody + recombinant for this target. See more →
ADAMTS: A disintegrin and metalloprotease with thrombospondin motifs; a family of 19 secreted zinc-dependent endopeptidases (clan MA, family M12B) distinguished from ADAMs by C-terminal thrombospondin type-1 repeats and the absence of a transmembrane domain. Members process procollagens and cleave versican, aggrecan, and von Willebrand factor in the extracellular matrix. See more →
ADAMTS13 (vWF protease): A secreted ADAMTS metalloprotease (EC 3.4.24.87; UniProt Q76LX8) that cleaves von Willebrand factor (vWF) at the Tyr1605–Met1606 bond within the A2 domain under shear stress, regulating platelet-thrombus size. Congenital or acquired ADAMTS13 deficiency causes thrombotic thrombocytopenic purpura (TTP). TPB catalogs a matched antibody + recombinant for this target. See more →
Ectodomain shedding: Proteolytic cleavage of the extracellular domain (ectodomain) of a transmembrane protein at a juxtamembrane site, releasing a soluble ectodomain fragment and retaining a membrane-anchored stub. Performed primarily by ADAM and MMP family proteases, this post-translational event regulates receptor density, ligand bioavailability, and downstream signaling cascades. See more →
Sheddase: Informal term for any protease that executes ectodomain shedding of cell-surface proteins. ADAM10 and ADAM17/TACE are the most extensively characterized sheddases, collectively responsible for releasing over 80 documented substrates including TNF-α, HER2, Notch, and APP ectodomains. Activity can be monitored with fluorogenic peptide substrates; see /guides/protease-activity-assays for assay-design guidance. See more →
Alpha-secretase (ADAM10): The proteolytic activity that cleaves amyloid precursor protein (APP) within the Aβ peptide sequence (between Lys687 and Leu688 in APP770), precluding amyloidogenic Aβ production. ADAM10 (EC 3.4.24.81) is the constitutive alpha-secretase in neurons; ADAM17 contributes under stimulated conditions. Cleavage yields soluble sAPPα and an 83-residue membrane stub (C83). See more →
Disintegrin domain: A ~90-residue non-catalytic domain in ADAM and ADAMTS proteases, located C-terminal to the metalloprotease domain. Structurally homologous to snake-venom disintegrins, it mediates protein–protein interactions, modulates substrate binding, and in some ADAMs directly engages integrin receptors via an RGD or ECD loop, influencing cell adhesion and migration. See more →
Cysteine-rich region: A conserved structural module present in ADAM proteases immediately C-terminal to the disintegrin domain. The cysteine-rich region contains a 'hypervariable region' (HVR) that confers substrate specificity and participates in the autoinhibitory 'cysteine-switch' interaction with the prodomain zinc-binding site during latency. Structural resolution by X-ray and cryo-EM has clarified its allosteric regulatory role. See more →
Pro-protein convertase cleavage: Processing of an ADAM or ADAMTS zymogen by furin-family proprotein convertases (e.g., furin, PC7) at a conserved RXXR motif within the trans-Golgi network, removing the inhibitory prodomain and generating the catalytically competent protease. This intracellular activation step controls the spatiotemporal availability of active sheddases at the cell surface. See /guides/zymogens-and-proenzymes for activation-mechanism context. See more →

Cysteine Cathepsins + Calpains

Cathepsin B: Lysosomal cysteine protease (EC 3.4.22.1; UniProt P07858) of the papain family. Functions as both an endopeptidase and exopeptidase (carboxydipeptidase). Implicated in extracellular matrix remodeling, apoptosis, and tumor invasion. Active at acidic pH; inhibited by E-64 and cystatins. TPB catalogs a matched antibody + recombinant for this target. See more →
Cathepsin K: Lysosomal cysteine protease (EC 3.4.22.38; UniProt P43235) of the papain family. The primary collagenase in osteoclasts, cleaving type I collagen at acidic pH. Central to bone resorption and a validated therapeutic target in osteoporosis. TPB catalogs a matched antibody + recombinant for this target. See more →
Cathepsin L: Lysosomal endopeptidase (EC 3.4.22.15; UniProt P07711) of the papain family. Broad substrate specificity; degrades extracellular matrix proteins and processes precursor proteins. Elevated in cancer, cardiovascular disease, and viral entry. Sensitive to E-64 and type-2 cystatins. TPB catalogs a matched antibody + recombinant for this target. See more →
Cathepsin S: Lysosomal cysteine protease (EC 3.4.22.27; UniProt P25774) of the papain family. Distinct among cathepsins for retaining activity at neutral pH. Critical for MHC class II antigen presentation via invariant-chain (Ii) degradation. Implicated in autoimmune disease, atherosclerosis, and pain signaling. TPB catalogs a matched antibody + recombinant for this target. See more →
Cathepsin V: Lysosomal cysteine endopeptidase (EC 3.4.22.43; UniProt O60911; also called Cathepsin L2) of the papain family. Expressed predominantly in thymus, testis, and corneal epithelium. Participates in cortical thymic epithelial cell antigen processing. Shares ~80% sequence identity with Cathepsin L but has a distinct tissue distribution. TPB catalogs a matched antibody + recombinant for this target. See more →
Cathepsin H: Lysosomal cysteine protease (EC 3.4.22.16; UniProt P09668) of the papain family. Unique in acting as both an endopeptidase and aminopeptidase. Involved in lysosomal protein turnover and pulmonary surfactant processing. A mini-chain disulfide-linked to the heavy chain governs its exopeptidase mode. TPB catalogs a matched antibody + recombinant for this target. See more →
Papain-family cysteine protease: Clan CA (MEROPS), family C1 proteases sharing structural homology with plant papain. Defined by a catalytic triad (Cys-His-Asn) and a bilobal fold. Includes all lysosomal cathepsins (B, K, L, S, V, H, etc.), as well as bleomycin hydrolase and cytosolic variants. Activated by reduction of the active-site cysteine. See more →
Lysosomal protease: Any protease localized to lysosomes and optimally active at the acidic luminal pH (~4.5–5.0). Includes cysteine cathepsins (B, D is aspartyl, L, S, K, H, V), aspartyl cathepsins (D, E), and some serine hydrolases. Responsible for bulk intracellular protein degradation, antigen processing, and organelle turnover via autophagy. See more →
Endolysosomal cleavage: Proteolytic processing occurring within the endosomal–lysosomal pathway as vesicles acidify from early endosomes (pH ~6.5) to late lysosomes (pH ~4.5). Cysteine and aspartyl cathepsins are sequentially activated along this gradient, mediating receptor downregulation, proprotein maturation, and pathogen degradation. Disruption underlies lysosomal storage disorders. See more →
Cystatin: Superfamily of tight-binding, reversible inhibitors of papain-family (C1) and legumain-family (C13) cysteine proteases. Defined by a conserved QxVxG motif and hairpin loops that occlude the protease active site. Three families in humans: type 1 (stefins A/B; intracellular), type 2 (cystatins C, D, S; secreted), and type 3 (kininogens; multidomain plasma proteins).
Cystatin C: Type 2 cystatin (UniProt P01034; gene CST3); 13.3 kDa secreted inhibitor of papain-family proteases including Cathepsins B, H, K, L, and S. Constitutively expressed and freely filtered at the glomerulus, making it a standard serum biomarker of glomerular filtration rate (GFR). Also implicated in amyloid angiopathy via L68Q variant dimerization. See more →
E-64 inhibitor: trans-Epoxysuccinyl-L-leucylamido(4-guanidino)butane; an irreversible, cell-permeable inhibitor of papain-family cysteine proteases (Clan CA, family C1). Covalently modifies the active-site Cys via epoxide alkylation. Used experimentally to confirm cysteine-cathepsin activity in lysate and cell-based assays. See /guides/protease-activity-assays for assay-design guidance. See more →
Calpain: Family of calcium-dependent intracellular cysteine proteases (MEROPS Clan CA, family C2). Fifteen mammalian paralogs share a catalytic domain with a Cys-His-Asn triad. Unlike cathepsins, calpains function at cytosolic pH (~7.0–7.4) and require Ca²⁺ for activation. Substrates include cytoskeletal proteins, kinases, and phosphatases; implicated in apoptosis, necrosis, and neurodegeneration. See more →
Calpain-1 (μ-calpain): Ubiquitous heterodimeric calpain (80 kDa CAPN1 catalytic subunit + 28 kDa CAPNS1 regulatory subunit; UniProt P07384/P04632). Activated by micromolar Ca²⁺ concentrations in vitro. Involved in platelet activation, NMDA-receptor–mediated synaptic plasticity, and ischemic neuronal injury. TPB catalogs a matched antibody + recombinant for this target. See more →
Calpain-2 (m-calpain): Ubiquitous heterodimeric calpain (80 kDa CAPN2 catalytic subunit + 28 kDa CAPNS1 regulatory subunit; UniProt P17655/P04632). Requires millimolar Ca²⁺ for activation in vitro, though membrane phospholipids and autolysis lower the threshold in vivo. Implicated in focal adhesion disassembly, cell migration, and post-ischemic neurodegeneration. TPB catalogs a matched antibody + recombinant for this target. See more →
Calpastatin: Endogenous, Ca²⁺-dependent protein inhibitor specific to calpains-1 and -2 (UniProt P20810; gene CAST). Contains up to four tandem inhibitory domains (L, I, II, III, IV), each capable of blocking one calpain heterodimer. Inhibition is reversible and requires Ca²⁺ binding by both calpain and calpastatin. Dysregulation is linked to muscle wasting and Alzheimer's disease.
Calcium-dependent cysteine protease: A cysteine protease requiring Ca²⁺ ion binding for catalytic activation or structural stabilization. The calpain family is the primary mammalian example: Ca²⁺ induces conformational rearrangement that repositions the Cys-His-Asn catalytic triad. Distinct from lysosomal cathepsins, which are activated by acidic pH rather than calcium. Relevant in ischemia-reperfusion and neuronal excitotoxicity models. See more →

Serine Proteases

Trypsin: A serine endoprotease (EC 3.4.21.4; family S1, clan PA) secreted by the pancreas as inactive trypsinogen. Cleaves peptide bonds C-terminal to Arg and Lys residues. Activates other zymogens in the digestive cascade. UniProt P07477 (human). TPB catalogs matched antibody + recombinant for this target. See more →
Chymotrypsin: A pancreatic serine endoprotease (EC 3.4.21.1; family S1) cleaving peptide bonds C-terminal to bulky hydrophobic residues (Phe, Trp, Tyr). Secreted as chymotrypsinogen; activated by trypsin. Catalytic triad: Ser195, His57, Asp102. UniProt P17538 (human CTRB1). See more →
Elastase: A family of serine endoproteases (EC 3.4.21.36; family S1) that hydrolyze elastin and other extracellular matrix proteins at small aliphatic residues (Ala, Val, Gly). Includes pancreatic elastase 1 and 2 (ELA1, ELA2A) and leukocyte forms. Implicated in ECM remodeling and inflammatory tissue damage. See more →
Neutrophil Elastase: A leukocyte-derived serine protease (EC 3.4.21.37; ELANE; UniProt P08246) stored in azurophil granules and released during neutrophil degranulation. Degrades elastin, collagen, and proteoglycans; also activates cytokines. Dysregulation drives COPD, cystic fibrosis, and ARDS. TPB catalogs matched antibody + recombinant for this target. See more →
Kallikrein: A subfamily of serine proteases (family S1, clan PA) comprising 15 human tissue kallikreins (KLK1–KLK15) and plasma kallikrein (KLKB1). They process kininogens, growth factors, and extracellular matrix proteins. Several are validated cancer biomarkers. Structurally defined by conserved Asp-His-Ser catalytic triad. See more →
Tissue Kallikrein: Tissue kallikrein (KLK1; EC 3.4.21.35; UniProt P06870) is a glandular serine protease that liberates Lys-bradykinin (kallidin) from low-molecular-weight kininogen. Expressed in kidney, pancreas, and salivary glands. Regulates blood pressure and renal sodium handling. TPB catalogs matched antibody + recombinant for this target. See more →
Plasma Kallikrein: A circulating serine protease (KLKB1; EC 3.4.21.34; UniProt P03952) that cleaves high-molecular-weight kininogen to release bradykinin, activating the contact activation pathway of coagulation. Also activates plasminogen and factors XII and XI. Secreted as prekallikrein; activated by factor XIIa. See more →
Granzyme: A family of serine proteases (family S1) stored in cytotoxic T lymphocyte and NK cell secretory granules. Released during immune synapses to induce target-cell apoptosis. Human granzymes A, B, H, K, and M differ in substrate specificity and apoptotic mechanism. All share the canonical Asp-His-Ser triad. See more →
Granzyme A: A cytotoxic lymphocyte serine protease (GZMA; EC 3.4.21.78; UniProt P12544) that functions as a disulfide-linked homodimer. Cleaves after Arg/Lys residues; triggers caspase-independent apoptosis via the SET complex and single-strand DNA nicking. TPB catalogs matched antibody + recombinant for this target. See more →
Granzyme B: The dominant apoptosis-inducing granzyme in cytotoxic lymphocytes (GZMB; EC 3.4.21.79; UniProt P10144). Cleaves substrates after Asp residues, directly activating caspase-3 and -7 and processing Bid. Perforin-dependent delivery is essential for cytotoxicity. Widely used as a CTL activation marker. TPB catalogs matched antibody + recombinant for this target. See more →
Granzyme K: A tryptase-like serine protease (GZMK; UniProt P49863) expressed in NK cells and CD8⁺ T cells. Cleaves after Arg/Lys residues and induces mitochondria-dependent apoptosis independent of caspase-3. Also reported to activate pro-IL-18 and modulate extracellular matrix. TPB catalogs matched antibody + recombinant for this target. See more →
Granzyme H: A chymotryptic serine protease (GZMH; UniProt P20718) expressed predominantly in NK cells. Cleaves C-terminal to aromatic and aliphatic residues; induces caspase-independent cell death and degrades adenoviral DNA-binding protein to restrict viral replication. Less characterized than granzymes A and B. See more →
MASP (Mannose-Binding Lectin-Associated Serine Protease): Serine proteases (MASP-1, EC 3.4.21.97; MASP-2, EC 3.4.21.104; and MASP-3) that associate with pattern-recognition molecules (MBL, ficolins) to activate the lectin pathway of complement. MASP-2 cleaves C4 and C2 to form C3 convertase. Structurally related to C1r and C1s of the classical pathway. See more →
HTRA (High-Temperature Requirement A): A conserved family of serine proteases (family S1C) characterized by a trypsin-like catalytic domain and one or two PDZ domains. Four human paralogs (HTRA1–4) regulate protein quality control, TGF-β signaling, and mitochondrial integrity. HTRA1 and HTRA2 are implicated in age-related macular degeneration and Parkinson's disease, respectively. See more →
TMPRSS (Transmembrane Serine Protease): A subfamily of type II transmembrane serine proteases (family S1) anchored at the cell surface. Human members include TMPRSS2, TMPRSS4, hepsin, matriptase, and DESC1. They activate growth factors, process viral envelope proteins, and regulate epithelial ion channels. Dysregulation is linked to cancer invasion and viral entry. See more →
TMPRSS2: A type II transmembrane serine protease (EC 3.4.21.-; UniProt O15393) expressed on airway and gut epithelium. Primes SARS-CoV-2 spike protein by cleavage at the S2′ site, facilitating membrane fusion. Also processes influenza hemagglutinin and is androgen-regulated, relevant to prostate cancer. TPB catalogs matched antibody + recombinant for this target. See more →
Furin: A ubiquitously expressed proprotein convertase (PCSK3; EC 3.4.21.75; UniProt P09958) of the subtilisin-like family S8. Cleaves substrates at paired basic motifs (Arg-X-Lys/Arg-Arg↓) in the trans-Golgi network and at the cell surface. Activates viral fusion proteins, anthrax toxin, and growth factor precursors. TPB catalogs matched antibody + recombinant for this target. See more →
PCSK (Proprotein Convertase Subtilisin/Kexin): A nine-member family of subtilisin-like serine proteases (family S8; PCSKs 1–9) that process secretory pathway precursor proteins. Members include furin (PCSK3), PC1/3, PC2, PACE4, and PCSK9 (which targets LDL receptors for degradation). Each member has distinct tissue distribution, pH optima, and substrate preferences. See more →
Plasminogen: The zymogen precursor of plasmin (UniProt P00747; 810 aa), synthesized in the liver and circulating in plasma at ~2 µM. Contains five kringle domains mediating fibrin binding. Activated by tissue plasminogen activator (tPA) or urokinase (uPA) via cleavage of the Arg561–Val562 bond. Central to fibrinolysis. See more →
Plasmin: The active serine protease (EC 3.4.21.7; family S1) derived from plasminogen by tPA or uPA cleavage. Degrades fibrin clots, activates MMPs, and processes growth factors and complement components. Broadly specific for Lys/Arg residues. Inhibited by α2-antiplasmin and α2-macroglobulin. TPB catalogs matched antibody + recombinant for this target. See more →
Fibrinolysis: The enzymatic dissolution of fibrin clots, primarily by plasmin generated from plasminogen via tPA and uPA. Regulated by inhibitors including PAI-1 (SERPINE1) and α2-antiplasmin. Physiologically balances coagulation; excess fibrinolysis leads to bleeding, while deficit promotes thrombosis. Also activates latent MMPs and growth factors. See more →
Serpin: Serine protease inhibitors (SERPINs) are a superfamily of ~500 proteins defined by a conserved ~350 aa fold containing a reactive center loop (RCL). They inhibit target proteases via a suicide-substrate mechanism, forming a covalent acyl-enzyme complex. Includes antithrombin, PAI-1, α1-antitrypsin, and C1-inhibitor. Some serpins are non-inhibitory. See more →
Antithrombin: A plasma serpin (SERPINC1; UniProt P01008) that irreversibly inhibits thrombin (factor IIa), factor Xa, and other coagulation proteases. Heparin binding accelerates inhibition >1000-fold by inducing an RCL conformational change. Hereditary antithrombin deficiency confers elevated venous thromboembolism risk. TPB catalogs matched antibody + recombinant for this target. See more →
PAI-1 (SERPINE1): Plasminogen activator inhibitor-1 (PAI-1; SERPINE1; UniProt P05121) is the primary inhibitor of tPA and uPA, acting as a fast-binding serpin (k_assoc ~10⁷ M⁻¹s⁻¹). Elevated in metabolic syndrome, fibrosis, and cancer. Exists in active, latent, and substrate conformations. TPB catalogs matched antibody + recombinant for this target. See more →
C1-Inhibitor (SERPING1): A plasma serpin (SERPING1; UniProt P05155) that inhibits C1r and C1s of the classical complement pathway, MASP-1 and MASP-2 of the lectin pathway, and contact activation proteases factor XIIa and plasma kallikrein. Hereditary deficiency (HAE) causes recurrent angioedema. Heavily glycosylated; ~105 kDa apparent on SDS-PAGE. TPB catalogs matched antibody + recombinant for this target. See more →

Aspartic Proteases

Aspartic Protease Catalytic Mechanism: Aspartic proteases (clan AA, family A1) use two catalytic aspartate residues — typically Asp32 and Asp215 (pepsin numbering) — to activate a water molecule that performs nucleophilic attack on the scissile peptide bond. The reaction proceeds via a tetrahedral intermediate without a covalent enzyme-substrate intermediate. Optimal activity generally occurs at acidic pH (1–5). See more →
BACE1 (β-Secretase 1): BACE1 (Beta-site APP-cleaving enzyme 1; EC 3.4.23.46; UniProt P56817) is a type-I transmembrane aspartic protease of the pepsin family. It cleaves amyloid precursor protein (APP) at the β-site, initiating amyloidogenic processing and Aβ peptide generation. A primary therapeutic target in Alzheimer's disease research. TPB catalogs a matched antibody + recombinant for this target. See more →
BACE2: BACE2 (Beta-site APP-cleaving enzyme 2; EC 3.4.23.45; UniProt Q9Y5Z0) is a transmembrane aspartic protease homologous to BACE1 (~52% amino acid identity). It cleaves APP at a non-amyloidogenic site and is expressed predominantly in the pancreas and gut. BACE2 has been implicated in β-cell function and type 2 diabetes. TPB catalogs a matched antibody + recombinant for this target. See more →
Cathepsin D: Cathepsin D (EC 3.4.23.5; UniProt P07339) is a lysosomal aspartic endopeptidase of the pepsin family, ubiquitously expressed. It degrades intracellular proteins, processes antigens, and regulates apoptosis. Synthesized as a 43 kDa prepro-enzyme; mature heavy chain is ~34 kDa. Elevated expression is a marker in several carcinomas. TPB catalogs a matched antibody + recombinant for this target. See more →
Cathepsin E: Cathepsin E (EC 3.4.23.34; UniProt P14091) is a non-lysosomal intracellular aspartic protease of the pepsin family, predominantly expressed in immune and gastric mucosal cells. It functions as a disulfide-linked homodimer (~100 kDa) and participates in MHC class II antigen presentation and immune regulation. TPB catalogs a matched antibody + recombinant for this target. See more →
Pepsin: Pepsin (EC 3.4.23.1) is the principal gastric aspartic endopeptidase, produced from pepsinogen via autocatalytic cleavage at pH <5. It preferentially cleaves peptide bonds adjacent to hydrophobic residues (Phe, Leu, Trp) and functions optimally at pH 1.5–2.5. The archetype of the pepsin family (A1) and a reference standard for aspartic protease biochemistry. See more →
Pepsinogen: Pepsinogen is the catalytically inactive zymogen precursor of pepsin, secreted by gastric chief cells. The ~44 kDa proenzyme is activated at pH <5 by cleavage of a ~44-residue propeptide, which acts as an intramolecular inhibitor occluding the active site. Serum pepsinogen I/II ratios are used clinically as non-invasive markers of gastric mucosal atrophy. See more →
Renin: Renin (EC 3.4.23.15; UniProt P00797) is a highly substrate-specific aspartic protease secreted by juxtaglomerular cells of the kidney. It cleaves angiotensinogen at the Leu10–Val11 bond to generate angiotensin I, the rate-limiting step of the renin–angiotensin–aldosterone system (RAAS). Renin inhibitors (e.g., aliskiren) are used as antihypertensives. TPB catalogs a matched antibody + recombinant for this target. See more →
Napsin A: Napsin A (EC 3.4.23.-; UniProt P57086) is an aspartic protease of the pepsin family expressed in lung type II pneumocytes and renal proximal tubules. It participates in surfactant protein B maturation. Widely used as an immunohistochemical marker to distinguish primary lung adenocarcinoma from other pulmonary malignancies. TPB catalogs a matched antibody + recombinant for this target. See more →
Presenilin: Presenilins (PSEN1, UniProt P49768; PSEN2, UniProt P49810) are the catalytic aspartyl protease subunits of the γ-secretase complex, containing two transmembrane aspartate residues essential for intramembranous proteolysis. Autosomal dominant mutations in PSEN1/2 are the most common cause of familial early-onset Alzheimer's disease. They are classified within the GxGD-type intramembrane proteases. See more →
γ-Secretase (Gamma-Secretase): γ-Secretase is a heterotetrameric intramembrane aspartyl protease complex comprising Presenilin (catalytic subunit), Nicastrin, APH-1, and PEN-2. It cleaves type I transmembrane proteins within their transmembrane domains, including APP (releasing Aβ peptides) and Notch (releasing NICD). A validated target in Alzheimer's disease and oncology research. See more →
Pepstatin A: Pepstatin A is a microbially derived hexapeptide inhibitor (from Streptomyces spp.) that potently inhibits most aspartic proteases (Ki ~1 nM for pepsin, cathepsin D, renin). It contains the unusual amino acid statine, which mimics the tetrahedral transition state of aspartic protease catalysis. Used as a reference inhibitor and mechanistic probe in aspartic protease assays. See more →
Amyloidogenic Processing: Amyloidogenic processing is the sequential cleavage of APP first by BACE1 (β-secretase) at the β-site, generating a soluble ectodomain (sAPPβ) and a membrane-retained C99 fragment, followed by γ-secretase cleavage of C99 to release Aβ peptides (predominantly Aβ40 and Aβ42). Aggregation of Aβ42 into plaques is a hallmark of Alzheimer's disease pathology. See more →
APP (Amyloid Precursor Protein) Processing: APP (UniProt P05067) is a type I transmembrane glycoprotein processed via two competing pathways. Non-amyloidogenic processing involves α-secretase (ADAM10/17) cleavage within the Aβ domain, precluding Aβ formation. Amyloidogenic processing via BACE1 then γ-secretase generates Aβ peptides. The balance between these pathways is a central determinant of Alzheimer's disease risk. See more →

Activity Assay Techniques

Fluorogenic substrate: A protease substrate that becomes fluorescent upon enzymatic cleavage. A quenching moiety suppresses signal in the intact peptide; cleavage separates fluorophore from quencher, producing measurable emission. Enables continuous, real-time activity measurement in microplate formats. See /guides/fluorogenic-substrates-for-proteases for assay-design guidance. See more →
FRET substrate: A fluorogenic substrate in which fluorescence resonance energy transfer (FRET) between a donor fluorophore and an acceptor quencher suppresses signal when the peptide is intact. Protease cleavage disrupts FRET, releasing donor emission. Ratiometric detection of donor/acceptor signal improves dynamic range over single-fluorophore designs. See /guides/fluorogenic-substrates-for-proteases. See more →
AMC fluorophore: 7-Amino-4-methylcoumarin (AMC); a coumarin-based fluorophore released by protease cleavage of AMC-conjugated peptide substrates. Excitation ~360 nm, emission ~460 nm. Free AMC exhibits ~20–40× greater fluorescence than the conjugated form, providing high signal-to-noise in cysteine and serine protease activity assays. See /guides/fluorogenic-substrates-for-proteases. See more →
MCA-DNP FRET pair: (7-Methoxycoumarin-4-yl)acetyl (MCA) donor paired with 2,4-dinitrophenyl (DNP) acceptor/quencher. MCA emits at ~393 nm; DNP quenches via inner-filter and FRET when within ~10–20 Å. Widely used in MMP and ADAM substrate peptides (e.g., MOCAc-series). Cleavage separates the pair, restoring MCA fluorescence. See /guides/fluorogenic-substrates-for-proteases. See more →
EDANS-DABCYL FRET pair: 5-[(2-Aminoethyl)amino]naphthalene-1-sulfonic acid (EDANS; donor, excitation ~340 nm, emission ~490 nm) paired with 4-((4-(dimethylamino)phenyl)azo)benzoic acid (DABCYL; quencher). Used in HIV protease, cathepsin, and BACE1 FRET substrates. DABCYL quenches EDANS emission in intact peptide; protease cleavage abolishes FRET. See /guides/fluorogenic-substrates-for-proteases. See more →
Chromogenic substrate: A protease substrate that releases a colored product upon cleavage, typically para-nitroaniline (pNA; absorbance ~405 nm). Requires no specialized optics; absorbance is measured in a standard plate reader. Sensitivity is generally lower than fluorogenic formats, but chromogenic substrates are well-suited for endpoint assays and validation of continuous fluorogenic data. See /guides/protease-activity-assays. See more →
Suc-LLVY-AMC (calpain substrate): Succinyl-Leu-Leu-Val-Tyr-AMC; a fluorogenic tetrapeptide substrate cleaved by calpain-1 (EC 3.4.22.52), calpain-2 (EC 3.4.22.53), and the 20S proteasome chymotryptic site. Hydrolysis of the Tyr–AMC bond releases free AMC (ex/em ~360/460 nm). Calpain selectivity requires calcium supplementation and proteasome inhibitor controls. See /guides/protease-activity-assays. See more →
Z-FR-AMC (cathepsin B/L substrate): Benzyloxycarbonyl-Phe-Arg-AMC; a fluorogenic dipeptide substrate with selectivity toward cathepsin B (EC 3.4.22.1) and cathepsin L (EC 3.4.22.15), both papain-family cysteine proteases. Cleavage at the Arg–AMC bond liberates AMC (ex/em ~360/460 nm). Assays are conducted at mildly acidic pH (5.5–6.0) reflecting lysosomal conditions. See /guides/protease-activity-assays. See more →
MOCAc-GKPILFFRLK (cathepsin D substrate): A FRET peptide substrate (MCA-Gly-Lys-Pro-Ile-Leu-Phe-Phe-Arg-Leu-Lys-DNP) for cathepsin D (EC 3.4.23.5; UniProt P07339), an aspartyl protease active at pH 3.5–5.0. Cathepsin D cleaves the Phe–Phe bond, separating MCA donor from DNP quencher and restoring MCA fluorescence (~393 nm). Also cleaved by cathepsin E. See /guides/protease-activity-assays. See more →
Zymography: A gel-based technique for detecting protease activity in which substrate (e.g., gelatin, casein) is co-polymerized within an SDS-PAGE gel. After electrophoresis, proteins are renatured and the gel is incubated to allow in-gel digestion. Proteolytic bands appear as clear zones against a uniformly stained background, enabling size-based identification of active species. See /guides/protease-activity-assays. See more →
Gelatin zymography: A zymography variant in which gelatin (denatured collagen) is incorporated as substrate, primarily used to detect MMP-2 (gelatinase A; EC 3.4.24.24) and MMP-9 (gelatinase B; EC 3.4.24.35). After SDS-PAGE and renaturation, gelatinolytic bands are visualized by Coomassie staining. Conditioned medium is the typical sample source. TPB catalogs matched antibody + recombinant for both MMP-2 and MMP-9. See more →
Casein zymography: A zymography variant using casein as the co-polymerized substrate, suited for detecting serine proteases (e.g., plasminogen activators, kallikreins) and certain MMPs active against casein, including MMP-3 and MMP-7. Caseinolytic activity appears as clear bands after Coomassie staining. Sensitivity and background differ from gelatin formats; substrate choice should match enzyme class. See /guides/protease-activity-assays. See more →
IC50: Half-maximal inhibitory concentration; the inhibitor concentration that reduces enzyme activity by 50% under defined substrate and enzyme concentrations. IC50 is condition-dependent and not an intrinsic enzyme constant. It can be converted to Ki using the Cheng-Prusoff equation when substrate concentration and Km are known. Used routinely to rank inhibitor potency in protease screening campaigns. See more →
Ki (inhibition constant): The equilibrium dissociation constant for the enzyme–inhibitor complex; a substrate-concentration-independent measure of inhibitor potency (units: M). Determined by Dixon plot, Cheng-Prusoff conversion from IC50, or global fitting of velocity data. Lower Ki indicates tighter binding. Ki distinguishes competitive, uncompetitive, and mixed inhibition mechanisms when combined with varied substrate concentrations. See more →
Km (Michaelis constant): The substrate concentration at which reaction velocity equals half of Vmax under steady-state conditions (units: M or µM). Km approximates substrate–enzyme affinity when kcat << k−1; it is determined by nonlinear regression of v vs. [S] data to the Michaelis-Menten equation. Km values guide substrate concentration selection in protease activity assays to ensure sub- or saturating conditions. See more →
kcat: Catalytic rate constant (turnover number); the maximum number of substrate molecules converted to product per active site per second (units: s⁻¹). Calculated as Vmax divided by total enzyme concentration ([E]T). The ratio kcat/Km defines catalytic efficiency and is useful for comparing protease activity across substrates or enzyme variants under identical assay conditions. See more →
Specific activity: Enzyme activity normalized to protein mass, expressed as nmol product·min⁻¹·mg⁻¹ (or equivalent units). Specific activity accounts for variation in enzyme concentration and purity across preparations, enabling comparison between lots or sources. For recombinant proteases, specific activity is a standard QC metric confirming that purified protein is catalytically competent. See more →
Initial velocity: The reaction rate measured during the early linear phase of a progress curve, before substrate depletion, product inhibition, or enzyme inactivation become significant (typically <10% substrate consumed). Initial velocity (v0) is the primary observable in Michaelis-Menten kinetics. Fluorogenic assays should be validated to confirm linearity with respect to both time and enzyme concentration before v0 is reported. See more →
Steady-state kinetics: A kinetic framework assuming the enzyme–substrate complex (ES) concentration remains approximately constant during the assay, i.e., d[ES]/dt ≈ 0. Described by the Michaelis-Menten equation; parameters Km, Vmax, and kcat are derived from initial velocity measurements at varying [S]. Steady-state conditions require [S] >> [E] and are standard for characterizing protease activity in solution-phase fluorogenic assays. See more →

Antibody Validation Terminology

Polyclonal Antibody: A heterogeneous mixture of immunoglobulins produced by multiple B-cell clones, each recognizing a distinct epitope on the same immunogen. Polyclonals offer broad target coverage and high signal in Western blot and IHC, but lot-to-lot variability requires re-validation when serum lots change. See more →
Rabbit Polyclonal: A polyclonal antibody raised in New Zealand White or similar rabbit strains via repeated immunization with a defined antigen. Rabbit IgG typically yields higher affinity and greater sensitivity than mouse polyclonals. Affinity purification against the original immunogen is standard practice to reduce background. See more →
Monoclonal Antibody: An antibody secreted by a single hybridoma or recombinant expression clone, recognizing one defined epitope with fixed affinity. Lot-to-lot consistency is the primary advantage. Monoclonals can fail if the target epitope is masked by post-translational modification or denaturation during SDS-PAGE. See more →
Affinity Purification: Chromatographic isolation of antigen-specific immunoglobulins from crude antiserum by passage over an immobilized immunogen or peptide column, followed by low-pH elution. Removes non-specific IgG, reducing background in Western blot and IHC. Reported as 'immunogen affinity-purified' on validated datasheets. See more →
Immunogen: The antigen preparation used to raise an antibody response in the host animal. Common formats include full-length recombinant protein, KLH-conjugated synthetic peptide (typically 10–20 residues), or GST-fusion fragment. Immunogen sequence and species of origin determine predicted cross-reactivity and epitope location. See more →
Epitope: The specific molecular surface — linear (sequence-dependent) or conformational (structure-dependent) — recognized by an antibody's complementarity-determining regions (CDRs). SDS-PAGE denaturing conditions favor detection of linear epitopes; native IP and flow cytometry may require conformational epitopes to be intact. See more →
Cross-reactivity: Binding of an antibody to an antigen other than its primary target, typically due to shared epitope sequence across species orthologs or paralogous protein family members. Reported as 'predicted' (by sequence homology) or 'validated' (by empirical testing). Cross-reactivity within MMP or serine protease families is common and should be confirmed experimentally. See more →
Specificity: The ability of an antibody to bind its intended target and not closely related proteins. Confirmed by knockout cell lysate, siRNA knockdown, or peptide competition controls. High specificity is especially critical when antibodies target conserved domains shared across a protein family, such as the MMP catalytic domain. See more →
Sensitivity: The minimum amount of target antigen detectable by an antibody under defined assay conditions, typically expressed as the lowest concentration (ng/mL) or total protein mass (pg) generating a signal above background. Sensitivity is assay-format-dependent: ELISA and ECL Western blot differ substantially from colorimetric IHC. See more →
Western Blot Positive Control: A sample of known antigen content run alongside experimental lysates to confirm antibody performance, transfer efficiency, and expected molecular weight. Recombinant protein fragments are preferred over cell lysates because antigen concentration is defined. TPB catalogs recombinant protein standards matched to corresponding antibodies for this purpose. See more →
Recombinant Standard: A bacterially or mammalian-expressed protein of defined sequence, purity (≥85% by SDS-PAGE), and concentration, used as a quantitative or qualitative reference in Western blot, ELISA, and activity assays. Eliminates variability inherent in cell lysate controls. TPB produces recombinant protease and inhibitor standards matched to catalog antibodies. See more →
Knockout Validation: Antibody specificity confirmation using isogenic cell lines or tissues in which the target gene has been ablated (CRISPR/Cas9 or homologous recombination). A specific antibody shows no band at the expected molecular weight in knockout lysate. Considered the most stringent single-method validation by the International Working Group for Antibody Validation (IWGAV). See more →
Orthogonal Validation (Uhlén 5-Pillar Framework): A multi-strategy antibody validation framework described by Uhlén et al. (2016, Nature Methods) comprising five independent pillars: genetic strategies (knockout/knockdown), orthogonal methods (RNA vs. protein correlation), independent antibodies, capture mass spectrometry, and protein expression profiling. No single pillar is universally sufficient; pillar selection depends on application. See more →
Domain-Specific Antibody: An antibody whose immunogen is restricted to a defined structural or functional domain — e.g., the prodomain, catalytic domain, or hemopexin domain of an MMP. Domain specificity allows discrimination between zymogen and active forms, or between family members sharing a conserved catalytic fold but divergent auxiliary domains. See more →
Superpooled Antibody (SPA): A defined mixture of affinity-purified polyclonal antibodies from multiple individual immunized animals, pooled to reduce lot-dependent performance variability. By averaging the epitope repertoire across donors, SPAs provide more consistent signal than single-donor serum lots while retaining the multi-epitope coverage of polyclonals. See more →
Western Blot Loading Control: An antibody detecting a constitutively expressed, abundant protein — most commonly GAPDH or β-actin — used to confirm equal protein loading across lanes and to normalize target band intensity. Loading controls should be validated for the specific cell/tissue type; some experimental conditions alter expression of canonical controls. See more →
GAPDH: Glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12; UniProt P04406, human). A glycolytic enzyme widely used as a Western blot loading control (~37 kDa). Expression is not invariant: GAPDH is upregulated under hypoxia and in some cancer lines, making it an unreliable normalizer in those contexts.
β-Actin: Cytoplasmic beta-actin (UniProt P60709, human; ~42 kDa), a ubiquitous cytoskeletal protein used as a Western blot loading control. Co-migrates with many proteins of interest near 40–45 kDa. Expression increases with cell proliferation and serum stimulation, warranting caution as a normalizer in growth-state experiments.
Secondary Antibody: An antibody directed against the constant (Fc) region of a primary antibody's host species IgG (e.g., anti-rabbit IgG for rabbit primaries). Carries a detection moiety — HRP, fluorophore, or biotin — enabling signal amplification. Species and subclass specificity must match the primary antibody to avoid background. See more →
HRP-Conjugated: Describes an antibody or streptavidin covalently coupled to horseradish peroxidase (EC 1.11.1.7). In the presence of hydrogen peroxide and a substrate (ECL chemiluminescent reagent or DAB for IHC), HRP generates a detectable signal. Conjugate activity diminishes over time; storage at 4°C with 50% glycerol extends shelf life.
Biotin-Conjugated: Describes an antibody labeled with biotin (vitamin B7), exploiting the near-irreversible biotin–streptavidin interaction (Kd ~10⁻¹⁵ M) for detection or capture. Used in ELISA sandwich assays, IHC with tyramide amplification, and proximity ligation assays. Endogenous biotin in liver and kidney tissue can produce false-positive IHC signal.

Recombinant Protein Production

Recombinant protein: A protein produced by expression of a cloned gene introduced into a heterologous host cell. The gene of interest is inserted into an expression vector, transfected or transformed into the host, and the host's translational machinery synthesizes the encoded protein. Widely used to generate protease targets, antibody antigens, and assay standards at defined purity. See more →
Expression system: The combination of host organism, vector, and regulatory elements used to produce a recombinant protein. Common systems include bacterial (E. coli), yeast (P. pastoris), insect cell (Sf9/baculovirus), and mammalian (HEK293, CHO). System choice determines yield, folding fidelity, and post-translational modification profile. See more →
HEK293: Human embryonic kidney 293 cells, a widely used mammalian expression host derived from transformed human fetal kidney cells. HEK293 supports complex N- and O-linked glycosylation, disulfide bond formation, and mammalian-like post-translational processing, making it well-suited for producing secreted proteases and Fc fusion proteins with human-relevant glycoforms. See more →
CHO (Chinese hamster ovary): Chinese hamster ovary cells, the dominant industrial mammalian expression host for recombinant therapeutics. CHO cells provide robust growth in suspension culture, human-compatible (though not identical) glycosylation, and scalable yields. Commonly used for producing glycosylated proteases and Fc fusion proteins where glycan structure influences activity or half-life. See more →
E. coli expression: Bacterial recombinant protein production using Escherichia coli, typically strains BL21(DE3) or Rosetta, with IPTG-inducible T7 promoter vectors. Advantages include rapid growth and high yield; limitations include lack of eukaryotic glycosylation and tendency toward inclusion body formation for disulfide-rich proteins. Suitable for producing unglycosylated protease domains and inhibitors. See more →
Sf9 / Baculovirus: Sf9 are Spodoptera frugiperda insect cells used with recombinant baculovirus (typically Autographa californica multiple nucleopolyhedrovirus, AcMNPV) to express recombinant proteins. The system supports disulfide bond formation and some N-glycosylation (high-mannose type), making it useful for larger, folded eukaryotic proteins where bacterial expression fails but full mammalian glycosylation is not required. See more →
Codon optimization: The process of rewriting a gene's codon usage to match the preferred codons of the expression host without altering the amino acid sequence. Rare codons in the original organism can stall ribosomes in the host. Optimization typically increases translational efficiency and soluble yield, particularly relevant when expressing human proteases in E. coli. See more →
His tag: A short polyhistidine sequence (typically 6×His) appended to the N- or C-terminus of a recombinant protein to enable purification by immobilized metal affinity chromatography (IMAC). His-tagged proteins bind Ni²⁺ or Co²⁺ resin under native or denaturing conditions and are eluted with imidazole. The tag is small (~0.8 kDa) and often left in place for downstream detection. See more →
FLAG tag: An eight-amino-acid hydrophilic epitope tag (DYKDDDDK) recognized by anti-FLAG monoclonal antibodies (e.g., clone M2). Commonly used for Western blot detection, immunoprecipitation, and affinity purification via anti-FLAG resin. Its hydrophilicity reduces interference with protein folding, and enterokinase cleaves immediately downstream of the sequence if tag removal is needed. See more →
GST tag: Glutathione S-transferase (GST; EC 2.5.1.18) fused to the N-terminus of a recombinant protein to facilitate purification on glutathione–Sepharose resin and elution with reduced glutathione. The 26 kDa tag can promote solubility of aggregation-prone proteins but may interfere with activity assays; it is typically removed with thrombin or PreScission protease after purification. See more →
MBP fusion: Maltose-binding protein (MBP; UniProt P0AEX9 in E. coli) fused to a recombinant protein of interest. At 42 kDa, MBP is one of the most effective solubility-enhancing tags for bacterial expression of otherwise insoluble proteins. Purification uses amylose resin with maltose elution. Commonly used for producing soluble protease domains that form inclusion bodies without the tag. See more →
Fc fusion: A recombinant protein in which the target sequence is genetically linked to the Fc region of an immunoglobulin (typically human IgG1). The Fc domain confers extended serum half-life (via FcRn recycling), facilitates homodimerization, and enables purification by Protein A/G affinity chromatography. Commonly used for producing bivalent cytokine receptors, protease inhibitors, and enzyme ectodomains. See more →
Affinity chromatography: A chromatographic technique that separates proteins based on specific, reversible binding to an immobilized ligand (e.g., Ni²⁺-NTA for His-tagged proteins, Protein A for Fc fusions, glutathione for GST fusions). A single affinity step typically achieves >90% purity from crude lysate, making it the first and often dominant step in recombinant protein purification workflows. See more →
Ni-NTA purification: Immobilized metal affinity chromatography (IMAC) using nickel ions chelated to nitrilotriacetic acid (NTA) resin. Histidine residues in a His-tag coordinate the Ni²⁺ ion, selectively capturing the tagged protein from lysate. Elution is achieved with 150–500 mM imidazole. Under-imidazole wash steps remove weakly bound host-cell contaminants. A standard first-capture step for His-tagged recombinant proteases. See more →
Size exclusion chromatography (SEC): A liquid chromatography technique that separates proteins by hydrodynamic radius as they pass through a porous stationary phase; larger molecules elute first. SEC is used as a polishing step to remove aggregates, truncations, and tag-cleaved contaminants after affinity purification, and analytically to confirm monodispersity and oligomeric state of a recombinant protein preparation. See more →
Endotoxin: Lipopolysaccharide (LPS) components of the outer membrane of Gram-negative bacteria (e.g., E. coli) that co-purify with recombinant proteins produced in bacterial systems. Endotoxin activates TLR4 signaling in mammalian cells, confounding cell-based assays at picogram-per-mL concentrations. Removal is achieved by Triton X-114 phase separation, anion-exchange chromatography, or endotoxin-removal resins. See more →
LAL assay: Limulus amebocyte lysate (LAL) assay; the gold-standard method for quantifying endotoxin in recombinant protein preparations. Lysate from horseshoe crab (Limulus polyphemus) blood cells undergoes a coagulation cascade in the presence of LPS; result is reported in Endotoxin Units (EU) per mg protein. Regulatory guidance (e.g., USP <85>) specifies acceptance limits for parenteral products. See more →
Lyophilization: Freeze-drying; a stabilization process in which a protein solution is frozen and then subjected to reduced pressure, causing ice to sublime directly to vapor (primary drying) followed by desorption of bound water (secondary drying). The resulting dry cake has extended shelf life at ambient or 4 °C storage. Excipients such as trehalose, mannitol, or BSA are typically included as lyoprotectants. See more →
Glycosylation: The enzymatic addition of oligosaccharide chains to specific amino acid residues: N-linked glycosylation occurs at Asn-X-Ser/Thr sequons in the ER; O-linked glycosylation occurs at Ser/Thr residues in the Golgi. Glycosylation affects protein folding, stability, half-life, and interactions. Bacterial expression systems do not support eukaryotic glycosylation; mammalian systems (HEK293, CHO) are required when glycans are functionally relevant. See more →
Post-translational modification (PTM): Any covalent chemical modification of a protein after ribosomal synthesis, including glycosylation, phosphorylation, proteolytic cleavage (e.g., zymogen activation), disulfide bond formation, acetylation, and ubiquitination. PTMs regulate protease activity, localization, and half-life. The expression system must be chosen to replicate the PTMs present on the native protein if functional fidelity is required. See more →
Lot-specific CoA: A Certificate of Analysis issued for a specific manufacturing lot of a recombinant protein, documenting identity (e.g., SDS-PAGE, Western blot), purity (% by densitometry or HPLC-SEC), concentration (A280 or BCA), endotoxin level (EU/mg by LAL), and functional activity (e.g., specific activity in a fluorogenic substrate assay). Lot-specific CoAs are essential for experimental reproducibility and regulatory traceability. See more →
Certificate of Analysis (CoA): A quality document accompanying each lot of a biological reagent, certifying that the material meets defined release specifications. For recombinant proteins, a CoA typically includes: protein identity, molecular weight confirmation, purity ≥ X% (method stated), concentration, endotoxin content, sterility status, storage conditions, and expiry. CoAs should be lot-specific; batch-to-batch variation makes lot-averaged CoAs insufficient for rigorous research. See more →

Disease Research Contexts

Alzheimer's Disease + BACE: Alzheimer's disease (AD) is a neurodegenerative disorder characterized by amyloid-β (Aβ) plaque accumulation and neurofibrillary tau tangles. BACE1 (β-site APP-cleaving enzyme 1; EC 3.4.23.46, UniProt P56817), an aspartyl protease of the pepsin family, is the rate-limiting β-secretase that cleaves amyloid precursor protein (APP) to initiate Aβ generation. BACE1 inhibition remains a primary therapeutic target in AD research. TPB catalogs a matched antibody + recombinant for this target. See more →
Cancer Invasion + MMP: Tumor cell invasion requires proteolytic degradation of basement membrane and stromal extracellular matrix. Matrix metalloproteinases (MMPs; EC 3.4.24.x), zinc-dependent endopeptidases, are central mediators: MT1-MMP (MMP-14) activates pro-MMP-2 at the cell surface, while MMP-9 and MMP-3 further remodel matrix to facilitate local invasion. Expression is upregulated in most solid tumors. TPB catalogs matched antibodies + recombinants across the MMP family. See more →
Tumor Metastasis: Tumor metastasis is the multistep process by which cancer cells disseminate from a primary site to colonize distant organs. Steps include intravasation, survival in circulation, extravasation, and secondary outgrowth. Proteases—including MMPs, uPA (EC 3.4.21.73), cathepsins B and L, and ADAMTSs—facilitate matrix degradation, growth factor release, and basement membrane breach at each stage. See more →
ECM Remodeling in Cancer: Extracellular matrix (ECM) remodeling in cancer involves coordinated protease-mediated degradation and deposition of collagen, fibronectin, laminin, and proteoglycans to create a permissive tumor microenvironment. Key enzymes include MMPs, ADAMTSs (aggrecanases), and serine proteases such as plasmin. Altered ECM stiffness and composition promote tumor growth, angiogenesis, and metastatic spread. See more →
Bone Remodeling + Cathepsin K: Bone remodeling is the continuous cycle of osteoclast-mediated resorption and osteoblast-mediated deposition. Cathepsin K (EC 3.4.22.38, UniProt P43235), a lysosomal cysteine protease of the papain family, is the dominant collagenase in osteoclasts, degrading type I collagen in the acidic resorption lacuna. It is the molecular target of odanacatib and related anti-resorptive drugs. TPB catalogs a matched antibody + recombinant for this target. See more →
Osteoclast: Osteoclasts are multinucleated, bone-resorbing cells of hematopoietic (monocyte/macrophage) lineage differentiated by RANKL/OPG signaling. They acidify the resorption lacuna via V-ATPase and secrete cathepsin K, MMP-9, and tartrate-resistant acid phosphatase (TRAP) to degrade mineralized matrix. Dysregulated osteoclast activity underlies osteoporosis, Paget's disease, and bone metastasis. See more →
Coagulation Cascade + Serine Proteases: The coagulation cascade is a sequential zymogen-activation network that culminates in fibrin clot formation. The central enzymes—factor VIIa (EC 3.4.21.21), factor Xa (EC 3.4.21.6), thrombin (EC 3.4.21.5), and factor XIIa—are serine proteases of the chymotrypsin fold (S1 family, MEROPS). Each cleaves peptide bonds C-terminal to specific basic residues, propagating a ~1,000,000-fold amplification of the coagulation signal. See more →
Thrombosis + ADAMTS13: Thrombosis is pathological intravascular clot formation. ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin motifs 13; EC 3.4.24.87, UniProt Q76LX8) cleaves ultra-large von Willebrand factor (VWF) multimers under shear stress, preventing spontaneous platelet aggregation. Severe ADAMTS13 deficiency—congenital or acquired via autoantibodies—causes thrombotic thrombocytopenic purpura (TTP). TPB catalogs a matched antibody + recombinant for this target. See more →
Von Willebrand Disease: Von Willebrand disease (VWD) is the most common inherited bleeding disorder, caused by quantitative or qualitative defects in von Willebrand factor (VWF; UniProt P04275), a large multimeric glycoprotein mediating platelet adhesion and acting as a carrier for factor VIII. Type 2A VWD specifically involves loss of high-molecular-weight multimers due to increased ADAMTS13-mediated cleavage or defective VWF multimerization. See more →
Inflammation + Neutrophil Elastase: During acute inflammation, activated neutrophils degranulate and release neutrophil elastase (NE; EC 3.4.21.37, UniProt P08246), a serine protease of the chymotrypsin family stored in azurophilic granules. NE cleaves elastin, collagen IV, fibronectin, and numerous cytokines/receptors, amplifying the inflammatory response. Dysregulated NE activity contributes to COPD, ARDS, and cystic fibrosis lung pathology. TPB catalogs a matched antibody + recombinant for this target. See more →
Mast Cell Biology + Chymase + Tryptase: Mast cells are tissue-resident innate immune cells that store and release serine proteases upon IgE-mediated or innate activation. Tryptase (EC 3.4.21.59; β-tryptase, UniProt Q15661) is a tetrameric trypsin-like enzyme; chymase (EC 3.4.21.39; UniProt P23946) is a chymotrypsin-like monomer. Both remodel ECM, activate cytokines, and amplify inflammatory cascades. Elevated tryptase is a clinical marker of systemic mastocytosis and anaphylaxis. TPB catalogs matched antibodies + recombinants for both targets. See more →
NETs (Neutrophil Extracellular Traps): Neutrophil extracellular traps (NETs) are web-like chromatin structures decorated with antimicrobial granule proteins—including neutrophil elastase (NE), cathepsin G, myeloperoxidase (MPO), and histones—released during NETosis, a specialized cell death program. NETs ensnare and kill pathogens but also promote immunothrombosis, tissue injury, and autoimmunity when dysregulated, as seen in SLE, COVID-19-associated coagulopathy, and sepsis. See more →
Cytotoxic T-Cell Killing + Granzyme/Perforin: Cytotoxic T lymphocytes (CTLs) and NK cells kill target cells via secretory lysosomes containing perforin (a pore-forming MACPF-domain protein) and granzymes (serine proteases; EC 3.4.21.x). Perforin facilitates granzyme entry into the target cell; granzyme B (UniProt P10144) cleaves caspase-3, BID, and ICAD, initiating apoptosis. Granzyme A cleaves SET, releasing DNase NM23-H1. TPB catalogs matched antibodies + recombinants for granzyme B. See more →
Apoptosis + Caspases: Apoptosis is programmed cell death executed by caspases (cysteine-aspartate proteases; EC 3.4.22.x, MEROPS C14 family). Initiator caspases (caspase-8, -9) activate executioner caspases (caspase-3, -6, -7), which cleave >600 cellular substrates including PARP, lamins, and ICAD, dismantling the cell. Intrinsic (mitochondrial) and extrinsic (death receptor) pathways converge at caspase-3 activation. TPB catalogs matched antibodies + recombinants for caspase-3 and caspase-8. See more →