PURIFICATION AND AUTOLYTIC DEGRADATION OF A CALPAIN-LIKE CALCIUM-DEPENDENT PROTEINASE FROM LOBSTER (HOMARUS-AMERICANUS) STRIATED-MUSCLE

1. A Ca2+-dependent proteinase (CDP) was purified from claw and abdominal muscles of the American lobster, Homarus americanus. It is one of four CDP activities previously identified in lobster striated muscles and designated CDP Ilb (Mykles D. L. and Skinner D. M., J. biol. Chem. 261, 9865-9871, 1986). The enzyme has a native molecular mass of 195 kDa and consists of a 95-kDa protein when separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. 2. CDP IIb underwent a Ca2+-dependent autoproteolysis in the absence of substrate, producing two fragments between 80 and 85 kDa coincident with a 50% reduction in the 95-kDa band. The remaining 95-kDa protein was resistant to further proteolysis, even after prolonged incubations. 3. These results suggest that CDP IIb is composed of two 95-kDa subunits that differ in susceptibility to autolytic degradation.