Testisin (Recombinant)

Frequently Asked Questions

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

Testisin (PRSS21) has a predicted molecular weight of ~34 kDa based on its 314 amino acid sequence (UniProt Q9Y6M0). However, the HEK293-expressed recombinant carries native-like N-linked glycosylation, so the apparent MW on SDS-PAGE typically runs between 38–45 kDa under reducing conditions. The diffuse banding pattern in this range is characteristic of glycoprotein heterogeneity and is not indicative of degradation. If you require sharper bands for MW estimation, treating with PNGase F prior to gel loading will collapse the smear to the predicted core peptide mass.

Is recombinant Testisin produced as a zymogen or active mature form, and how is it processed?

Testisin is synthesized as a single-chain zymogen that requires propeptide removal for activation. The HEK293-expressed recombinant is produced and purified as the active, processed form — the propeptide has been cleaved, exposing the mature catalytic domain with a functional Ser-His-Asp triad. Because activation can occur autocatalytically or via co-expressed furin-family convertases during mammalian cell secretion, our preparation avoids the need for exogenous enterokinase or factor Xa activation steps that E. coli-derived zymogens typically require.

What peptide substrates work best for Testisin serine protease activity assays in vitro?

Testisin is a trypsin-family serine protease (EC 3.4.21.-) with a preference for cleaving after basic residues (Arg, Lys). Fluorogenic substrates commonly used in the literature include Boc-Val-Pro-Arg-AMC and Z-Arg-Arg-AMC, both of which yield measurable RFU signals at low nanomolar enzyme concentrations. A practical starting point is 50–200 nM recombinant Testisin with 100 µM fluorogenic substrate in assay buffer (50 mM Tris-HCl pH 7.5, 150 mM NaCl, 0.01% Tween-20) at 37°C, reading at Ex/Em 360/460 nm. Include PMSF or AEBSF controls to confirm serine protease-dependent signal.

What buffer conditions are optimal for Testisin protease activity assays and does glycerol in the storage buffer interfere?

The storage buffer (50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol) is compatible with most downstream activity assays at typical working dilutions of 1:10 or greater, bringing glycerol to ≤1% in the final reaction — generally below the threshold for serine protease inhibition. Assay buffer pH 7.5–8.0 is optimal for trypsin-family activity. Avoid Ca²⁺ chelators such as EDTA (not relevant for serine proteases per se, but common in protease cocktails), and keep reducing agents like DTT below 1 mM, as high concentrations can affect disulfide-stabilized loop architecture in the catalytic domain.

What starting concentration of recombinant Testisin should I use for an IC50 inhibitor screening assay?

For IC50 determination, we recommend titrating enzyme concentration first to identify the linear range of substrate hydrolysis — typically 25–100 nM recombinant Testisin with 50–100 µM fluorogenic substrate (e.g., Boc-Val-Pro-Arg-AMC) gives a robust, inhibitor-sensitive signal window. Use the lowest enzyme concentration that yields a reliable signal-to-background ratio (≥5:1) to avoid stoichiometric titration artefacts, particularly important when screening tight-binding inhibitors. Reactions should be initiated by enzyme addition after pre-incubating inhibitor with substrate for 15 min at room temperature to allow equilibration.

Can I use recombinant Testisin as a Western blot positive control with the matched anti-Testisin antibody (RP-Testisin)?

Yes — this is one of the primary use cases for pairing REC-Testisin with RP-Testisin. The rabbit polyclonal antibody (RP-Testisin) was raised and validated against the same recombinant source protein, guaranteeing band detection on Western blot. Load 20–50 ng of REC-Testisin per lane alongside your experimental samples; the antibody reliably detects the glycosylated band in the 38–45 kDa range. This pairing also serves as a specificity control when validating RP-Testisin for detection of endogenous Testisin in testicular tissue lysates or Testisin-overexpressing cell lines.

How much recombinant Testisin should I load as a positive control for Western blot, and what band should I expect?

Load 20–50 ng of REC-Testisin per lane for a strong, clean signal with RP-Testisin at standard dilutions (typically 1:500–1:2000 for rabbit polyclonal antibodies; confirm with the RP-Testisin datasheet). On a 12% SDS-PAGE gel under reducing conditions, expect a diffuse band centered around 38–45 kDa due to HEK293-derived glycosylation. If you are comparing to endogenous Testisin in cell lysates — where expression levels can be low outside of testicular tissue — loading 20 ng of recombinant alongside 30–50 µg total cell lysate provides a useful signal-intensity reference.

How should I store and handle recombinant Testisin to maintain activity over time?

REC-Testisin is supplied in 50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol and should be stored at -20°C in single-use aliquots immediately upon receipt. Repeated freeze-thaw cycles measurably reduce serine protease activity — prepare working aliquots sized for one experiment before freezing. Once thawed, keep on ice and use within the same working session. For short-term use over 1–2 days, storage at 4°C is acceptable with 0.1% BSA added as a carrier stabilizer. Do not dilute to working concentration in advance and re-freeze; diluted enzyme loses activity faster than concentrated stock.