Calcium-dependent phosphorylation of bovine cardiac C-protein by phosphorylase kinase.

Phosphorylase kinase catalyzed the calcium-dependent phosphorylation of bovine cardiac C-protein. Phosphorylation of C-protein by phosphorylase kinase reached nearly 2 mol [32P]/mol C-protein. Tryptic phosphopeptide mapping and phosphoamino acid analysis indicated that phosphorylase kinase maybe phosphorylating some of the same seryl residues that undergo phosphorylation by cAMP-dependent protein kinase and that C-protein from bovine and chicken heart are structurally different. Bovine cardiac C-protein was not a substrate for a number of calcium and cyclic nucleotide-independent protein kinases, suggesting that phosphorylation of cardiac C-protein is restricted to protein kinases which are modulated by calcium and cAMP.