title: Phosphorylation of skeletal and cardiac muscle C-proteins by the catalytic subunit of cAMP-dependent protein kinase.
abstract: Catecholamines are known to influence the contractility of cardiac and skeletal muscles, presumably via cAMP-dependent phosphorylation of specific proteins. We have investigated the in vitro phosphorylation of myofibrillar proteins by the catalytic subunit of cAMP-dependent protein kinase of fast- and slow-twitch skeletal muscles and cardiac muscle with a view to gaining a better understanding of the biochemical basis of catecholamine effects on striated muscles. Incubation of canine red skeletal myofibrils with the isolated catalytic subunit of cAMP-dependent protein kinase and Mg-[gamma-32P]ATP led to the rapid incorporation of [32P]phosphate into five major protein substrates of subunit molecular weights (MWs) 143,000, 60,000, 42,000, 33,000, and 11,000. The 143,000 MW substrate was identified as C-protein; the 42,000 MW substrate is probably actin; the 33,000 MW substrate was shown not to be a subunit of tropomyosin and, like the 60,000 and 11,000 MW substrates, is an unidentified myofibrillar protein. Isolated canine red skeletal muscle C-protein as phosphorylated to the extent of approximately 0.5 mol Pi/mol C-protein. Rabbit white skeletal muscle and bovine cardiac muscle C-proteins were also phosphorylated by the catalytic subunit of cAMP-dependent protein kinase, both in myofibrils and in the isolated state. Cardiac C-protein was phosphorylated to the extent of 5-6 mol Pi/mol C-protein, whereas rabbit white skeletal muscle C-protein was phosphorylated at the level of approximately 0.5 mol Pi/mol C-protein. As demonstrated earlier by others, C-protein of skeletal and cardiac muscles inhibited the actin-activated myosin Mg2+-ATPase activity at low ionic strength in a system reconstituted from the purified skeletal muscle contractile proteins (actin and myosin).(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D002352:Carrier Proteins; D002417:Cattle; D004285:Dogs; D007700:Kinetics; D046911:Macromolecular Substances; D009124:Muscle Proteins / Q000302:isolation & purification / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011817:Rabbits; D000099163:Myosin Binding Protein C
chemical_list: D002352:Carrier Proteins; D046911:Macromolecular Substances; D009124:Muscle Proteins; D011494:Protein Kinases; D000099163:Myosin Binding Protein C