Activation Mechanism of Protein Kinases from Rat Tissues by Adenosine 3', 5'-Monophosphate

Abstract

3', 5'-Cyclic AMP (cyclic AMP)-dependent and independent protein kinases (protein kinase B₁ and B₂, respectively) and a cyclic AMP-binding protein (R-protein) are partially purified from rat liver. Although R-protein shows no kinase activity, it almost totally depresses protein kinase B₂ activity. Cyclic AMP relieves the kinase of the inhibition by R-protein. The treatment of protein kinase B₁ with cyclic AMP resolves the kinase into R-protein and protein kinase B₂. The evidence indicates that protein kinase B₁ is a complex of R-protein and protein kinase B₂, and that cyclic AMP may regulate the attachment of R-protein to the protein kinase.