Protein kinase C autophosphorylates by an intrapeptide reaction

The Ca2+-activated, phospholipid-dependent protein kinase C autophosphorylates by an intrapeptide reaction in a mixed micelle system in which the enzyme is a monomer. The rate of autophosphorylation in the micellar system is comparable to that observed in bilayer systems, where the enzyme may exist as an oligomer. Trypsinolysis of the enzyme reveals that both the regulatory and catalytic domains of the molecule are modified by the intrapeptide phosphorylation. Proteolysis of the enzyme to separate the two domains results in loss of ability to autophosphorylate. Furthermore, intact protein kinase C cannot phosphorylate either the cleaved regulatory or catalytic domains. Kinetic and proteolytic analyses suggest that intrapeptide phosphorylation is the predominant, and perhaps only, mechanism by which protein kinase C autophosphorylates. The intrapeptide modification of protein kinase C has intriguing implications for protein structure and regulation.