Purification and characterization of a low calcium requiring form of Ca2+-activated neutral protease from human platelets.

A low calcium requiring form of calcium activated neutral protease (mu-CANP) was purified to homogeneous state from a soluble fraction of human platelets. The purified protease was composed of two subunits of 80 K and 25 K proteins, judged by SDS polyacrylamide gel electrophoresis and the approximate molecular weight of 105 K was also confirmed by gel filtration technique. The purified enzyme was activated in the presence of micromolar concentration off Ca2+ and also activated with other divalent cations such as Sr2+, Ba2+, Mn2+, Ni2+. Leupeptin, antipain, an epoxysuccinate derivative (E-64), and alkylating agents were potent inhibitors of the purified enzyme.