although these observations might suggest , as others have concluded , that calpain is involved in the initiation of platelet activation by thrombin , we also found that : 1 ) substituting platelet membranes for intact platelets and decreasing the free ca2+ concentration below the threshold required for calpain activation did not diminish the effects of leupeptin on phosphoinositide hydrolysis and camp formation , 2 ) washing the platelets after incubation with leupeptin reversed the effects of the inhibitor , 3 ) permeabilizing the platelets with saponin did not enhance the inhibitory effects of leupeptin , and 4 ) leupeptin inhibited the proteolysis of fibrinogen and the hydrolysis of s2238 by thrombin .
C0006784
calpain
C0020291
hydrolysis