Calcium-Activated Proteases (Calpains)
Calpain (EC 188.8.131.52; Ca2(+)-dependent cysteine endopeptidase) exists in at least two forms. Calpain I requires low (or microM)-Ca2+ for activity and calpain II requires high (or mM)-Ca2+. Normally, intracellular calcium is quite low. It may be that Calpain I is involved in signal transduction via calcium transients and Calpain II may be active only when calcium influx is significant, such as in apoptosis. Both isozymes consist of one heavy (approx.80 kDa) and one light (approx. 30 kDa) subunit each. The heavy subunits of isozymes I and II are different gene products. The light subunit of both forms are identical. The regulation of protein expression and the physiological function of these protease is unknown.
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- Known Calcium-activated Proteases
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