Pepsin A (Recombinant)

Frequently Asked Questions

What molecular weight band should I expect for recombinant Pepsin A on SDS-PAGE?

The mature, active form of Pepsin A (UniProt P00790; PGA5) runs at approximately 34–35 kDa under reducing SDS-PAGE conditions, consistent with the processed enzyme after autocatalytic removal of the N-terminal prosegment (~44 residues). The zymogen precursor, pepsinogen A, would run closer to 42 kDa, but this HEK293-expressed preparation is supplied as the active, prosegment-cleaved form. Because HEK293 cells support N-linked glycosylation, you may observe a slight upward shift or diffuse banding relative to the theoretical unglycosylated MW; a tight band at ~34–36 kDa is the expected result.

Is this recombinant Pepsin A supplied as the zymogen (pepsinogen) or mature active enzyme?

This preparation is the mature, active enzyme — not the zymogen. Pepsinogen A undergoes autocatalytic cleavage of its ~44-residue N-terminal prosegment below pH 5, and this recombinant is processed to that active state prior to formulation. It is supplied in 50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol, where the enzyme is stable for storage but catalytically latent at neutral pH. Transfer to an acidic assay buffer (pH 2.0–4.0) is required to activate the enzyme for hydrolysis assays. Do not confuse the storage form with the inactive zymogen; no additional activation step is needed.

What substrates and assay buffer should I use to measure recombinant Pepsin A activity?

Pepsin A activity is most commonly measured at pH 2.0–3.5 in a citrate-phosphate or acetate assay buffer. The classic chromogenic substrate is acid-denatured hemoglobin (Anson assay), where released TCA-soluble peptides are quantified by Lowry or Folin reagent at ~660 nm. For fluorogenic kinetic assays, the internally quenched peptide substrate Lys-Pro-Ala-Glu-Phe-Nph-Ala-Leu (Mca/Dnp variants) is well characterized for aspartic proteases. Optimal pH is 2.0 for maximal velocity; activity drops sharply above pH 5 and is irreversibly denatured above pH 6. Use borosilicate or polypropylene vessels — Pepsin A adsorbs to certain plastics.

What starting concentration of recombinant Pepsin A should I use in a kinetic activity assay?

For initial rate kinetics with a fluorogenic peptide substrate, a working enzyme concentration of 1–5 nM in acidic assay buffer (pH 2.0–3.0) is a practical starting point, adjusting to keep reaction velocity in the linear range over 5–10 minutes. For the hemoglobin Anson assay, 0.01–0.1 µg/µL enzyme in 1 mL reaction volume at 37 °C for 10 minutes is a standard entry point. Titrate enzyme concentration to confirm linearity with respect to product formation before committing to inhibitor or mutant comparisons. This recombinant is supplied at ≥0.5 mg/mL; dilute immediately before use in pre-chilled acidic buffer.

How do I determine IC50 for a Pepsin A inhibitor using this recombinant?

Pre-incubate recombinant Pepsin A (1–2 nM final) with serial dilutions of your inhibitor at assay pH (2.0–3.5) for 15–30 minutes before initiating the reaction with substrate. For competitive inhibitors, ensure substrate concentration spans 0.3–3× Km to distinguish competitive from non-competitive mechanisms. Pepstatin A (Ki ~0.1 nM) is the standard positive-control inhibitor for aspartic proteases and should be included in every IC50 experiment as a benchmark. Avoid DMSO >1% v/v, which can artifactually reduce activity at acidic pH. Report IC50 values alongside substrate concentration used, as apparent IC50 shifts with [S] for competitive inhibitors.

Can I use recombinant Pepsin A as a positive control for Western blot with the TPB matched antibody?

Yes — this recombinant is the recommended positive control for the matched rabbit polyclonal antibody (SKU: RP-Pepsin A; /anti-pepsin-a-rabbit-polyclonal-antibody). Load 20–50 ng of recombinant Pepsin A per lane under reducing conditions; expect a clean band at ~34–36 kDa. The antibody and antigen are produced in the same laboratory and have been validated together for Western blot, so band identity is unambiguous. This pairing is particularly useful when setting up antibody dilutions against an unknown tissue lysate, giving you a defined-MW anchor band for normalization and ensuring you are detecting the mature enzyme form.

How much recombinant Pepsin A should I load for a Western blot positive control?

Load 20–50 ng per lane when using the matched antibody RP-Pepsin A under standard reducing SDS-PAGE conditions (4–12% or 10–15% Bis-Tris gels). At 20 ng, the band at ~34–36 kDa is readily detectable with an HRP-conjugated secondary at 1:5,000 and a standard ECL reagent with 1–3 minute exposure. If you are running gastric mucosal lysates alongside, load the recombinant control in a flanking lane rather than mixing, as the recombinant band may obscure closely migrating endogenous species. Do not boil the sample for more than 5 minutes — prolonged heating can cause aggregation artifacts above 100 kDa.

What are the storage and handling recommendations to preserve recombinant Pepsin A activity long-term?

Store at −20 °C in single-use aliquots immediately upon receipt. The formulation buffer — 50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol — maintains enzyme stability at neutral pH and prevents aggregation during freeze-thaw. Repeated freeze-thaw cycles measurably reduce specific activity; prepare working aliquots at 10–50 µg to match your typical experiment scale. Once thawed, keep on ice and use within 8 hours; do not re-freeze a thawed aliquot. Activity benchmarking against a hemoglobin hydrolysis assay on receipt is advisable to establish a baseline before committing the material to screening campaigns. Endotoxin is <0.1 EU/µg by LAL.