Stimulation by phospholipid of calcium-dependent phosphorylation of endogenous proteins from mammalian tissues

The occurrence of endogenous substrate proteins for calcium-dependent protein kinase, augmented by either phospholipid or calmodulin, was examined in extracts of several rat tissues. Pancreas, vas deferens, adrenal and liver were found to contain substrate proteins for phospholipid-sensitive protein kinase. Under the conditions utilized, only vas deferens exhibited substrate proteins for calmodulin-sensitive protein kinase. Phosphorylation of pancreatic substrate protein for phospholipid-sensitive protein kinase was rapid and highly sensitive to Ca2+, being detectable within 15 s following exposure to Ca2+ and phosphatidylserine and at concentrations of Ca2+ as low as 0.5 muM. These findings suggest that phospholipid-sensitive protein kinase system may serve to mediate some effects of Ca2+ in a variety of mammalian cell types.