Cross-Reactions of Adenosine 3',5'-Monophosphate-dependent Protein Kinase Systems from Rat Liver and Rabbit Skeletal Muscle

Protein kinases and regulatory proteins (R-proteins) which are capable of binding adenosine 3',5'-monophosphate (cyclic AMP) are partially purified from rat liver and rabbit skeletal muscle soluble fractions. The activity of either one of these kinases is almost totally depressed by R-protein from the homologous as well as from the heterologous tissue. As described earlier, cyclic AMP activates the inactive kinase by binding to R-protein resulting in the release of active kinase. These protein kinases phosphorylate the same specific seryl and threonyl residues of histone. Salmon sperm protamine and rabbit skeletal muscle glycogen phosphorylase b kinase serve as phosphate acceptors for both kinases. A possible role of the protein kinase systems in controlling cellular activities is also discussed briefly.