Calpain was purified from carp ordinary muscle by chromatography on DEAE-cellulose and Ultrogel ACA 34. The molecular weight was 80, 000 and the optimum pH 7.0. The half maximal activation of this calpain was obtained at 0.6-1.0mM Ca2+ and 4-5mM Sr2+, whereas Mg2+ did not activate this proteinase. Alkylating agents such as iodoacetic acid and N-ethylmaleimide inhibited the activity. From these rsults, carp calpain was classifined as calpain type II.
Phase microscopic observations showed that carp myofibrils were shortened and fragmented when incubated with the calpain. SDS-polyacrylamide gel electrophoresis showed that the calpain released from carp myofibrils α-actinin and some components whose molecular weights were >200, 000, 200, 000 43, 000, 37, 000, 19, 000, and 14, 000. The bands corredponding to troponin T and troponin I became fainter than those in intact myofibrils during incubation of myofibrils with this calpain.