Anti-Napsin-A Rabbit Polyclonal Antibody

Frequently Asked Questions

What molecular weight should I expect for Napsin-A on Western blot?

Napsin-A typically migrates at approximately 40–45 kDa on reducing SDS-PAGE, corresponding to the mature processed form of the 420-amino acid protein after signal peptide cleavage and propeptide removal. You may also observe a higher band near 50–55 kDa representing the proenzyme form, particularly in lysates from cells overexpressing NAPSA or in samples where proteolytic maturation is incomplete. The relative abundance of these forms depends on tissue type and lysosomal processing efficiency. Lung adenocarcinoma lysates and transfected cell lines typically show the mature 40–45 kDa band as the dominant species.

What is the recommended starting dilution for Napsin antibody in Western blot?

Start at 1:1000 dilution in blocking buffer for Western blot, which has been validated with this polyclonal. This dilution typically yields clean signal from 10–20 µg of total protein lysate derived from Napsin-A-expressing tissues such as lung adenocarcinoma cell lines or type II pneumocyte-enriched samples. If your expression level is lower or you are working with less abundant samples, you may titrate up to 1:500. Always include a Napsin-null control lysate to assess specificity, and optimize exposure times before adjusting antibody concentration to avoid saturating your signal.

Does this Napsin antibody recognize both the propeptide and mature forms?

This antibody targets the propeptide domain of Napsin-A, which means it recognizes epitopes present in both the zymogen (proenzyme) and any incompletely processed intermediate forms. However, the mature active enzyme, which has undergone propeptide cleavage in the lysosome, will lack this epitope and may not be detected efficiently. If you need to capture all maturation states, consider pairing this antibody with one targeting the catalytic domain. For Western blot of whole-cell lysates, you will typically detect precursor and intermediate forms; fully mature lysosomal Napsin-A may be underrepresented.

Which tissues or cell lines serve as good positive controls for Napsin-A expression?

Lung adenocarcinoma cell lines such as A549, H1975, or H1650 are robust positive controls, as Napsin-A is consistently and highly expressed in most lung adenocarcinomas. Normal lung tissue homogenate, particularly enriched for type II pneumocytes, also serves as a physiological positive control. Kidney cortex lysate, which contains proximal tubular epithelium, provides an additional endogenous source. For negative controls, use cell lines of non-pulmonary, non-renal origin such as HeLa, HEK293, or squamous carcinoma lines, which typically lack detectable Napsin-A. Always confirm expression levels by RT-PCR or prior publication before committing to a new line.

Is this Napsin antibody cross-reactive with mouse or rat samples?

This antibody has been validated for human samples and is predicted to cross-react with non-human primate species such as cynomolgus and rhesus monkey based on epitope homology. Cross-reactivity with mouse or rat Napsin-A has not been validated. Sequence alignment of the propeptide region shows moderate divergence between human and rodent orthologs, so binding efficiency in mouse or rat lysates cannot be guaranteed. If you require rodent reactivity, we recommend titrating the antibody against known positive control lysates from mouse or rat lung and comparing signal to a species-matched validated antibody before proceeding with experimental samples.

Can I use this antibody for immunohistochemistry on formalin-fixed paraffin-embedded lung tissue?

Yes, Triple Point Biologics antibodies are validated for immunohistochemistry, and Napsin-A is one of the most widely used IHC markers in surgical pathology for lung adenocarcinoma diagnosis. For FFPE sections, antigen retrieval is essential—citrate buffer at pH 6.0 with heat-induced epitope retrieval typically yields optimal staining. Start with a 1:100 to 1:200 dilution and titrate based on background and signal intensity in your tissue type. Expect strong cytoplasmic staining in type II pneumocytes and adenocarcinoma cells. Include normal lung and kidney cortex as positive controls and squamous carcinoma as a negative control.

How should I store the Napsin antibody and what is the expected shelf life?

Store the antibody at –20°C in single-use aliquots to avoid repeated freeze-thaw cycles, which can reduce titer and increase aggregation. The 100 µg pack size is supplied as a liquid or lyophilized format; if liquid, add glycerol to a final concentration of 50% and 0.02% sodium azide as preservative for long-term storage. Under these conditions, polyclonal antibodies typically retain activity for 12–24 months. Avoid storing diluted working solutions for more than one week at 4°C. Always centrifuge thawed aliquots briefly before use to pellet any aggregates that may contribute to background in Western blot or IHC.

Why might I see multiple bands on a Napsin Western blot?

Multiple bands likely reflect different maturation states of Napsin-A as it traffics through the secretory pathway and undergoes proteolytic processing in lysosomes. The proenzyme, intermediate cleavage products, and glycosylation variants can all be present simultaneously in cell lysates. Because this antibody targets the propeptide, you will preferentially detect precursor forms. Post-translational modifications, including N-linked glycosylation at multiple consensus sites, can also shift apparent molecular weight. If you observe a ladder or smear, treat lysates with PNGase F to assess glycosylation contribution. Degradation during sample preparation can also generate lower-molecular-weight fragments; always use fresh lysates and protease inhibitors.