Stimulation by phosphatidylserine and calmodulin of calcium-dependent phosphorylation of endogenous proteins from...

The Ca2+-dependent phosphorylation of a number of proteins in the cytosol of the rat or guinea pig cerebral cortex was profoundly stimulated by phosphatidylserine; calmodulin, on the other hand, had only a minimal effect. The Ca2+-dependent phosphorylation of different proteins from the total particulate fraction of the same tissue, in comparison, was specifically stimulated by either phosphatidylserine or calmodulin. The present findings, in line with the phospholipid-sensitive Ca2+-dependent protein kinase recently recognized, suggest an involvement of phospholipid in regulating Ca2+-dependent phosphorylation of endogenous substrate proteins. This new system presumably functions independent or in a complementary manner with the calmodulin-sensitive Ca2+-dependent protein phosphorylation system previously reported by others.