Characterization of two adenosine 3′,5′-monophosphate-dependent protein kinases from rat liver☆

Abstract Two adenosine 3′,5′-monophosphate (cyclic AMP)-dependent protein kinases are partially purified from rat liver soluble fraction by ammonium sulfate fractionation, followed by DEAE-Sephadex and hydroxylapatite column chromatography. Both kinases are dissociated by cyclic AMP into a common active protein kinase and regulatory proteins which differ from each other in their affinities for the cyclic nucleotide. Experiments with diisopropyl fluorophosphate as a protease inhibitor suggest that the two cyclic AMP-dependent protein kinases do not represent simply artifacts due to proteolysis during the isolation procedure.