Napsin B (Recombinant)

Frequently Asked Questions

What molecular weight should I expect for recombinant Napsin B on SDS-PAGE or Western blot?

The full-length human Napsin B precursor is 420 amino acids, giving a predicted MW of ~46 kDa. However, HEK293-expressed material carries N-linked glycosylation consistent with the native secreted form, so the apparent MW on reducing SDS-PAGE typically runs at 50–55 kDa. Under non-reducing conditions, intramolecular disulfide bonds can cause slight mobility shifts. If you are running a Western blot positive control alongside RP-NapsinB antibody, expect your band in the 50–55 kDa window rather than at the theoretical unmodified mass.

Is this recombinant Napsin B the zymogen form or the mature processed form? Does it need activation?

Napsin B is synthesised naturally as a zymogen requiring proteolytic removal of its propeptide to reach the catalytically active form. The Triple Point Biologics REC-NapsinB is supplied as the active, processed enzyme — propeptide cleavage has been carried out during production in HEK293 cells, mirroring the maturation that occurs in the secretory pathway. No additional activation step is required before use in enzymatic assays. If your experiment specifically requires the zymogen form, contact us before ordering, as this preparation is not the precursor.

What substrates does recombinant Napsin B cleave and what activity assay should I use?

As a member of the aspartyl protease family, Napsin B cleaves substrates at low pH using two catalytic aspartate residues. Fluorogenic peptide substrates designed for aspartyl proteases — such as those based on the cleavage motif recognized by cathepsin D or pepsin — are a practical starting point. Activity is typically measured in 100 mM sodium acetate, pH 3.5–4.5, using a substrate concentration near Km (commonly 10–50 µM). Confirm activity is abolished by pepstatin A (a pan-aspartyl protease inhibitor) as a specificity control. Reported enzyme concentrations for kinetic assays typically begin at 5–50 nM.

What buffer is recombinant Napsin B supplied in and what are the optimal assay buffer conditions?

REC-NapsinB is supplied in 50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol — a storage buffer chosen to maintain stability, not optimised for catalysis. For enzymatic assays, transfer the enzyme into an acidic activity buffer: 100 mM sodium acetate or citrate-phosphate buffer at pH 3.5–4.5, where aspartyl proteases are active. Keep glycerol ≤1% in the assay to avoid fluorescence interference. Add BSA (0.01–0.1%) as a carrier if working at sub-nanomolar enzyme concentrations to reduce non-specific adsorption to tube walls.

What starting concentration of recombinant Napsin B should I use for IC50 inhibitor screening?

For IC50 determinations, begin with an enzyme concentration of 5–20 nM in assay buffer (pH 3.5–4.5) and titrate inhibitor across at least 8–10 concentrations spanning 3 logs. Working near or below the enzyme Km for your fluorogenic substrate gives the most accurate apparent Ki. Pre-incubate enzyme with inhibitor for 15–30 minutes at 37°C before initiating the reaction with substrate, particularly for slow-binding inhibitors. Pepstatin A at 1 µM serves as a full inhibition positive control. Confirm DMSO tolerance up to 1% v/v, as higher concentrations can destabilise aspartyl protease activity.

Can I use REC-NapsinB as a positive control for Western blot with the RP-NapsinB polyclonal antibody?

Yes — REC-NapsinB and RP-NapsinB are matched in-house at Triple Point Biologics and guaranteed compatible for this application. Load 50–100 ng of recombinant protein per lane on a standard 10–12% SDS-PAGE gel under reducing conditions. Expect a band at 50–55 kDa (reflecting glycosylation). The RP-NapsinB rabbit polyclonal is validated for Western blot and provides a clean positive control signal at this loading, useful both for antibody titration and for confirming endogenous Napsin B detection in cell or tissue lysates running at the same apparent MW.

How much recombinant Napsin B should I load to validate RP-NapsinB antibody performance in a new Western blot protocol?

For antibody validation, a two-point loading of 25 ng and 100 ng per lane allows you to confirm linearity of signal and establish the antibody's dynamic range. Run alongside a cell lysate known to express Napsin B (e.g., lung adenocarcinoma lines) to demonstrate concordance between recombinant and endogenous bands at ~50–55 kDa. Use RP-NapsinB at its recommended working dilution (refer to the RP-NapsinB datasheet at /anti-napsinb-rabbit-polyclonal-antibody). Including a no-primary negative control lane is essential to distinguish specific signal from background.

How should I store and handle recombinant Napsin B to preserve enzymatic activity long-term?

Store REC-NapsinB at -20°C in the single-use aliquots as supplied. The 10% glycerol in the storage buffer (50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol) acts as a cryoprotectant and prevents ice-crystal damage to the protein structure. Avoid repeated freeze-thaw cycles — each cycle can cause measurable activity loss for aspartyl proteases with disulfide-dependent tertiary structure. On the day of use, thaw on ice and dilute directly into pre-cooled assay buffer. Do not vortex; mix by gentle pipetting. Aliquots are stable for up to 12 months at -20°C when stored correctly.