Phosphorylation of cardiac troponin inhibitory subunit (troponin I) and tropomyosin-binding subunit (troponin T) by cardiac phospholipid-sensitive Ca2+-dependent protein kinase.
Cardiac phospholipid-sensitive Ca2+-dependent protein kinase phosphorylated cardiac troponin inhibitory subunit (troponin I) and tropomyosin-binding subunit (troponin T), present either as the free form or as the troponin-tropomyosin complex. Exhaustive phosphorylation of troponin I and of troponin T revealed that 1.7 and 2 mol of phosphate was incorporated/mol of the subunits respectively. Cyclic AMP-dependent protein kinase, though incorporating 0.8 mol of phosphate/mol of troponin I, was unable to phosphorylate troponin T. Phosphorylation of troponin I (apparent Km = 3.4 microM; Vmax. = 2.6 mumol/min per mg of enzyme) or troponin T (apparent Km = 0.3 microM; Vmax. = 0.5 mumol/min per mg of enzyme) by the Ca2+-dependent enzyme was inhibited by various agents, such as adriamycin, palmitoylcarnitine, trifluoperazine, melittin and N-(6-aminohexyl)-5-chloronaphthalene-1-sulphonamide (compound W-7). Ca2+ antagonists (such as verapamil), forskolin and ouabain were ineffective. These findings indicate that troponin I and troponin T were effective substrates for this species of Ca2+-dependent protein kinase, suggesting its potential regulatory role in the contractile activity of myofibrils modulated by troponin.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D000242:Cyclic AMP / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D009124:Muscle Proteins / Q000378:metabolism*; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism*; D010743:Phospholipids / Q000494:pharmacology; D010766:Phosphorylation; D011493:Protein Kinase C; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D014336:Troponin / Q000378:metabolism*; D019210:Troponin I; D020107:Troponin T
D009124:Muscle Proteins; D010743:Phospholipids; D047428:Protein Kinase Inhibitors; D014336:Troponin; D019210:Troponin I; D020107:Troponin T; D000242:Cyclic AMP; D011494:Protein Kinases; D011493:Protein Kinase C; D002118:Calcium