Purification and Characterization of a Calcium-Dependent Protease from Rat Liver

A calcium-dependent protease, previously identified in rat liver and designated peak II [DeMartino, G. N. (1981) Arch. Biochem. Biophys. 211, 253–257], was purified and characterized. The calcium-dependent proteolytic activity was accounted for by an 80 000-dalton protein. Depending on the method of purification, we found that this protease could be associated with a 28 000-dalton subunit, which was devoid of protease activity. The catalytic characteristics of the two different forms of the protease were indistinguishable. Each was half-maximally activated by approximately 250 µM calcium.