Purified cyclic GMP-dependent protein kinase catalyzes the phosphorylation of cardiac troponin inhibitory subunit (TN-1).
Cyclic AMP- and cGMP-dependent protein kinases catalyze the phosphorylation of cardiac troponin inhibitory subunit (TN-I). Unlike many substrates utilized by both kinases, TN-I is rapidly phosphorylated using relatively low concentrations of the cGMP-dependent protein kinase (0.01 to 0.1 micrometer). At low concentrations of cAMP- and cGMP-dependent protein kinases, approximately twice as much total phosphate is incorporated into TN-I using the cAMP-dependent enzyme. At higher enzyme concentrations, 1 mol of phosphate/mol of TN-I is found using either enzyme. Maximal levels of cAMP- and CGMP-dependent protein kinases do not catalyze additive phosphorylation, suggesting that the two enzymes catalyze the phosphorylation of the same site on TN-I. The results support the concept of overlapping substrate specificity for cAMP- and cGMP-dependent protein kinases, but suggest that cardiac troponin contains additional specificity determinants for the cGMP-dependent protein kinase not found in several other protein substrates.
D000818:Animals; D002417:Cattle; D000242:Cyclic AMP / Q000494:pharmacology; D006152:Cyclic GMP / Q000494:pharmacology*; D004789:Enzyme Activation; D007700:Kinetics; D008168:Lung / Q000201:enzymology; D046911:Macromolecular Substances; D009124:Muscle Proteins; D009206:Myocardium; D011494:Protein Kinases / Q000378:metabolism*; D014336:Troponin
D046911:Macromolecular Substances; D009124:Muscle Proteins; D014336:Troponin; D000242:Cyclic AMP; D011494:Protein Kinases; D006152:Cyclic GMP