Adenosine 3′:5′-cyclic monophosphate- and guanosine 3′:5′-cyclic monophosphate-dependent protein kinases: Possible homologous proteins

Abstract
The properties of purified bovine liver adenosine cyclic monophosphate (cAMP)- and bovine lung guanosine cyclic monophosphate (cGMP)-dependent protein kinases were compared. Several physical characteristics of the 2 enzymes were similar, including size, shape, affinity for cyclic nucleotide binding and Km for ATP. The amino acid compositions of the 2 proteins indicated a close composition homology (70-90%). Both cyclic nucleotide-dependent protein kinases catalyzed phosphorylation of rat liver pyruvate kinase (EC 2.7.1.40) and fructose 1,6-diphosphatase (EC 3.1.3.11), rabbit skeletal muscle glycogen synthase (EC 2.4.1.11) and phosphorylase b kinase (EC 2.7.1.38), and calf thymus histone H2b. The phosphorylation of several synthetic peptides and of trypsin-sensitive and trypsin-insensitive sites in glycogen synthase suggested similar recognition sites on the protein substrates for the 2 kinases. The cAMP-dependent protein kinase was the better catalyst with each protein or peptide substrate. The 2 enzymes possibly evolved from a common ancestral protein.

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