title: Regulatory subunit of the type I cAMP-dependent protein kinase as an inhibitor and substrate of the cGMP-dependent protein kinase.
abstract: The regulatory subunit of the type I cAMP-dependent protein kinase (Rt) serves as a substrate for the phosphotransferase reaction catalyzed by cGMP-dependent protein kinase (Km = 2.2 microM). The reaction is stimulated by cGMP when RI . cAMP is the substrate, but not when nucleotide-free RI is used. The cGMP-dependent protein kinase catalyzes the incorporation of 2 mol of phosphate/mol of RI dimer in the presence of cAMP and a self-phosphorylation reaction to the extent of 4 mol of phosphate/mol of enzyme dimer. In the absence of cAMP, RI is a competitive inhibitor of the phosphorylation of histone H2B (Ki = 0.25 microM) and of the synthetic peptide substrate Leu-Arg-Arg-Ala-Ser-Leu-Gly (Ki = 0.15 microM) by the cGMP-dependent enzyme. Nucleotide-free RI also inhibits the intramolecular self-phosphorylation of cGMP-dependent protein kinase. The inhibition of the phosphorylation reactions are reversed by cAMP. The catalytic subunit of cAMP-dependent protein kinase does not catalyze the phosphorylation of RIand does not significantly alter the ability of RI to serve as a substrate or an inhibitor of cGMP-dependent protein kinase. These observations are consistent with the concept that the cGMP- and cAMP-dependent protein kinases are closely related proteins whose functional domains may interact.
mesh_terms: D000818:Animals; D002417:Cattle; D000242:Cyclic AMP / Q000494:pharmacology*; D006152:Cyclic GMP / Q000494:pharmacology*; D007700:Kinetics; D008168:Lung / Q000201:enzymology; D046911:Macromolecular Substances; D009132:Muscles / Q000201:enzymology; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D046911:Macromolecular Substances; D000242:Cyclic AMP; D011494:Protein Kinases; D006152:Cyclic GMP