Calpain 1 (CAPN1)

Calpain (calcium-dependent protease) is an intracellular protease that requires calcium for its catalytic activity. Two isozymes, calpain I (mu-calpain) and calpain II (m-calpain), with different calcium requirements, have been identified. Both are heterodimers composed of L (large, catalytic, 80 kD) and S (small, regulatory, 30 kD) subunits. The isozymes share an identical S subunit (CAPNS1), with the differences arising from the L subunits, L1 (CAPN1) and L2 (CAPN2). The mammalian calpains include ubiquitous, stomach-specific, and muscle-specific proteins. The ubiquitous enzymes consist of heterodimers with distinct large, catalytic subunits associated with a common small, regulatory subunit. Calpain-1 catalytic subunit is the large subunit of the ubiquitous enzyme, calpain 1.