Pappalysin-2 (Recombinant)

Frequently Asked Questions

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

The PAPPA2 open reading frame encodes 1,791 amino acids, giving a predicted unglycosylated molecular weight of approximately 200 kDa. Because this recombinant is expressed in HEK293 cells, N-linked glycosylation adds significant mass; expect the band to migrate at approximately 220–250 kDa under denaturing, reducing SDS-PAGE conditions. Batch-to-batch glycan heterogeneity can produce a diffuse or doublet band in this range — this is normal and does not indicate degradation. Purity is confirmed at >90% by Coomassie-stained SDS-PAGE prior to release.

What processing or isoform state is this recombinant Pappalysin-2 — proform or mature enzyme?

This recombinant is produced and secreted as the processed, mature form of PAPPA2 from HEK293 cells. The signal peptide is cleaved co-translationally, and the product represents the catalytically active secreted enzyme rather than an unprocessed proform. PAPPA2 does not require a separate prodomain removal step in vitro before use in cleavage assays. If your experiment requires distinguishing proform versus mature PAPPA2 by Western blot, the matched rabbit polyclonal antibody (RP-Pappalysin2) is a reliable detection reagent for both forms.

What substrate does recombinant Pappalysin-2 cleave and at which bond?

PAPPA2's primary enzymatic activity is proteolytic cleavage of insulin-like growth factor binding protein-5 (IGFBP-5) at the Ser163–Lys164 peptide bond. This cleavage liberates IGF ligands from the IGFBP-5 complex, increasing local IGF bioavailability. PAPPA2 shows limited secondary activity toward IGFBP-3 but does not efficiently cleave IGFBP-1, -2, -4, or -6. For substrate-cleavage assays, recombinant IGFBP-5 is the appropriate primary substrate. Cleavage can be confirmed by the disappearance of intact IGFBP-5 (~30 kDa) and appearance of the characteristic N- and C-terminal fragments on reducing SDS-PAGE.

What buffer conditions are recommended for Pappalysin-2 activity assays in vitro?

The protein is supplied in 50 mM Tris-HCl pH 7.5, 150 mM NaCl, 10% glycerol, and 5 mM CaCl₂ — the CaCl₂ is essential for metalloproteinase stability and is included in this formulation specifically for PAPPA2. For activity assays, dilute into a compatible reaction buffer maintaining pH 7.4–7.5 and at least 1–2 mM CaCl₂. Avoid chelating agents (EDTA, EGTA) as these strip the catalytic zinc ion and abolish activity. DTT at concentrations above 1 mM can also reduce activity; if a reducing environment is required, use TCEP at ≤0.5 mM instead.

What starting concentration of recombinant Pappalysin-2 should I use in an IGFBP-5 cleavage assay?

A practical starting point is 50–200 nM recombinant PAPPA2 incubated with 500 nM–1 µM recombinant IGFBP-5 at 37°C for 2–16 hours, depending on the sensitivity of your readout. For gel-based cleavage assays, a 4-hour incubation at 100 nM PAPPA2 with 500 nM IGFBP-5 typically produces clearly visible fragment bands. For ELISA-based quantification of released IGF-I or residual intact IGFBP-5, titrate PAPPA2 from 10–500 nM to establish a linear dose-response range appropriate for your inhibitor or substrate concentration studies.

Can I use recombinant Pappalysin-2 as a positive control for Western blot with the RP-Pappalysin2 antibody?

Yes — this is one of the primary validated uses of this recombinant. The matched rabbit polyclonal antibody (RP-Pappalysin2; /anti-pappalysin-2-rabbit-polyclonal-antibody) is raised and validated in the same laboratory, ensuring epitope-antigen compatibility. Load 10–50 ng of recombinant PAPPA2 per lane alongside your cell lysate or conditioned medium samples. The recombinant will produce a clean band at ~220–250 kDa, serving as both a size reference and a sensitivity benchmark for the antibody dilution you are optimizing. This pairing is particularly useful when validating RP-Pappalysin2 for detection of endogenous PAPPA2 in placental or serum samples.

How much recombinant Pappalysin-2 should I load for Western blot positive control and at what antibody dilution?

Load 25–50 ng per lane for a standard positive control lane using RP-Pappalysin2. At this loading, the antibody performs reliably at 1:500–1:2,000 dilution with HRP-conjugated anti-rabbit secondary antibody and standard ECL detection. If you are working with conditioned medium where endogenous PAPPA2 is at low concentrations, include a 10 ng recombinant lane to verify antibody sensitivity at the lower end of your detection range. Avoid loading >100 ng, as signal saturation can obscure the glycosylation-related band diffuseness and may bleed into adjacent sample lanes.

How should I store and handle recombinant Pappalysin-2 to preserve enzymatic activity after arrival?

Upon receipt, briefly centrifuge the vial, then aliquot into single-use volumes appropriate for your assay scale — freeze immediately at -20°C. Repeated freeze-thaw cycles progressively reduce metalloproteinase activity; even two additional cycles can result in measurable loss of IGFBP-5 cleavage efficiency. For short-term use (up to 1 week), the protein is stable at 4°C in its supplied buffer. Do not dilute working stocks in water; maintain buffer ionic strength and the 5 mM CaCl₂ in any dilution buffer. Shelf life is 12 months from date of manufacture when stored continuously at -20°C.