Phosphatidylinositol-specific phospholipase C from bovine blood platelets. Inhibition by calmodulin-inhibitors--activation by ATP and ADP.

The phospholipase C-activity in crude extracts of bovine blood platelets is strongly inhibited by the calmodulin-inhibitors fluphenazine and calmidazolium in the mM range, and activated by ATP and ADP, but not by AMP. The activating effect is also shown by the nonhydrolysable ATP- and ADP-analogs alpha,beta- and beta,gamma-methyleneadenosine 5'-triphosphate and alpha,beta-methyleneadenosine 5'-diphosphate, thus indicating that it is an allosteric effect. The stimulation of the phospholipase C-activity by ATP is also detectable in some partially purified fractions of the crude platelet extract, but it is abolished on further purification of the enzyme.