Target Information

The calpains are calcium-dependent cysteine proteases that are widely expressed in mammalian systems. Both m-calpain (calpain II) and m-calpain (calpain I) are composed of an 80 kD subunit and a 30 kD subunit. Whereas the 30 kDa subunit is shared by both enzymes, the larger catalytic subunits are different and exhibit the distinct Ca++ requirements that are suggested by their names. Whereas m-calpain requires millimolar (mM) levels of calcium, m-calpain is active at micromolar (mM) concentrations of Ca++. In addition to the ubiquitously expressed m- and m- calpains, some tissue-specific calpains have been identified. The calpains appear to serve multiple physiological roles, and ideas concerning the functions of these enzymes are in a state of rapid flux.