LP85-Calpain, also known as lens-specific calpain, is an intracellular, calcium-dependent cysteine protease. LP-85 is identical to LP-82 calpain, except for the insert that distinguishes LP-85. The calpains have papain-like activity, thus the -pain nomenclature. Unlike M-calpain and m-calpain, which are ubiquitously expressed, LP-85 calpain was originally identified in rat lens. Like the other calpains, the endogenous calpain inhibitor, calpastatin, counters LP85. Because of the limited distribution and sequence differences, LP-85 calpain is thought to have different roles than the other calpain family members. The calpain family members consist of a common small subunit, and a large variable subunit. Domains in the large subunit include the amino terminal domain-I, the proteinase domain-II, domain-III, and the EF-hand domain-IV. RP1-LP85-Calpain recognizes latent and active LP85-calpain; the latent large subunit is 85 Kd, and the amino terminal truncation at activation yields an approximately 62 Kd form. A cascade of smaller forms can be seen with further activation. RP1-LP85-Calpain works well for Western Blotting applications, and when used against the reduced protein identifies bands at 85 Kd, 62 Kd, and a series of further cleaved active forms. RP1-LP85-Calpain will also bind to the non-reduced protein, and thus has application for immunoprecipitation, immunohistochemistry, and ELISA. Most cell types produce m-Calpain; since it is a cellular protein, cell lysate works well for Western blots. Rat and mouse and LP85-Calpain are detected with RP1-LP85-Calapin. A smaller band at about 58 KD is seen in human tissue samples; this may be a closely related species. A recommended starting concentration for Western blots is 1:1000 when using colorimetric substrates such as BCIP/NBT, and 1:5000 for chemiluminescent substrates. Higher concentrations of antibody may be needed for samples from more distantly related species.

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