PC-2 (Recombinant)

Frequently Asked Questions

What is the expected molecular weight of recombinant PC-2 on SDS-PAGE and Western blot?

The full-length human PC-2 precursor is 638 amino acids (~71 kDa predicted), but the mature, prodomain-cleaved form that reaches enzymatic competence runs at approximately 66–68 kDa under reducing SDS-PAGE conditions. Because this recombinant is expressed in HEK293 cells, N-linked glycosylation adds an additional 3–6 kDa of apparent mass, so expect a diffuse band in the 69–74 kDa range on Western blot. A faint higher-MW band representing incompletely processed precursor may also appear, particularly at higher loads.

Which processing form of PC-2 is this recombinant — full precursor, prodomain-cleaved, or mature enzyme?

This preparation corresponds to the autocatalytically processed, prodomain-removed mature form of PC-2 — the enzymatically competent species found in secretory vesicles. The prodomain (~9 kDa) is cleaved intramolecularly during transit through the Golgi/trans-Golgi network and is absent in the final product. HEK293 expression was chosen specifically because it recapitulates the regulated secretory pathway, enabling authentic prodomain removal and glycosylation that bacterial or insect-cell systems cannot provide for this calcium-dependent enzyme.

What substrates does PC-2 cleave and what cleavage motif should I design into a synthetic peptide substrate?

PC-2 cleaves after paired basic residues, with a strong preference for Lys-Arg↓ and Arg-Arg↓ motifs at the P1–P2 positions. For a fluorogenic activity assay, the peptide substrate Boc-Arg-Val-Arg-Arg-AMC (or the closely related pGlu-RTKR-AMC) is commonly used and produces a measurable increase in AMC fluorescence (Ex 380 nm / Em 460 nm). Physiological substrates include proglucagon (cleavage at the GLP-1 and glucagon junctions) and proopiomelanocortin. If designing a custom substrate, ensure a P4 position with a small or basic residue for optimal kcat/Km.

What buffer conditions and calcium concentration are optimal for a PC-2 activity assay?

PC-2 is a calcium-dependent serine protease with an absolute requirement for Ca²⁺ for proper active-site conformation. For in vitro activity assays, use 50 mM sodium acetate or MES pH 5.5–6.0 (reflecting the trans-Golgi/secretory vesicle environment) supplemented with 1–5 mM CaCl₂. The enzyme is largely inactive at neutral pH — activity drops sharply above pH 7.0. The storage buffer (50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol) is not suitable as an assay buffer; dilute into your pH 5.5–6.0 assay buffer immediately before use.

What starting concentration of recombinant PC-2 should I use for a fluorogenic peptide cleavage assay?

A useful starting point is 50–200 nM recombinant PC-2 in a 100 µL assay volume, with substrate (e.g., Boc-Arg-Val-Arg-Arg-AMC) at 50–200 µM. At 100 nM enzyme and 100 µM substrate in 50 mM sodium acetate pH 5.8 / 2 mM CaCl₂ / 0.01% Triton X-100, AMC release is typically linear for 30–60 minutes at 37°C. Titrate enzyme concentration to keep initial velocity in the linear range before running inhibitor panels or IC₅₀ experiments. Include a no-enzyme and a heat-inactivated control in each plate.

Can I use PC-2 (Recombinant) as a Western blot positive control for the RP-PC2 matched antibody?

Yes — that is a primary validated use case for this product. Load 20–50 ng of recombinant PC-2 per lane alongside your cell or tissue lysates. The matched rabbit polyclonal antibody RP-PC2 (see /anti-pc-2-rabbit-polyclonal-antibody) is raised from the same antigen preparation used to characterize this recombinant, so band identity and apparent MW are directly comparable across experiments. This pairing is particularly useful when setting up detection in new tissue types or when troubleshooting weak endogenous signal in non-neuroendocrine cell lines that express PC-2 at low levels.

How much recombinant PC-2 should I load for a positive control lane when validating the RP-PC2 antibody?

For routine Western blot antibody validation, load 25–50 ng per lane. At 25 ng with RP-PC2 at a 1:1,000–1:2,000 dilution, you should observe a clean band at ~69–74 kDa after standard 1-hour ECL exposure on PVDF membrane. If you are titrating antibody concentration or comparing lot-to-lot performance, a 3-point dilution series (10 ng, 25 ng, 50 ng) of this recombinant alongside islet cell or hypothalamic lysate provides an informative dynamic-range reference. Do not exceed 100 ng per lane — overloading can cause smearing that obscures glycosylation heterogeneity.

How should I handle, dilute, and store recombinant PC-2 to preserve activity across multiple experiments?

The protein is supplied in 50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol and stored at -20°C in single-use aliquots. Avoid repeated freeze-thaw cycles — each cycle measurably reduces specific activity for calcium-dependent serine proteases. Upon receipt, aliquot immediately if the supplied format does not match your per-experiment volume. For activity assays, dilute into cold assay buffer immediately before use and equilibrate to 37°C just prior to the reaction. Purity is >95% by SDS-PAGE; endotoxin is <0.1 EU/µg by LAL assay, making this preparation suitable for cell-based and primary culture experiments.