Effect of substitution of troponin C in cardiac myofibrils with skeletal troponin C or calmodulin on the Ca2+- and Sr2+-sensitive ATPase activity.
Troponin C was removed almost completely from the porcine cardiac myofibrils by the same extraction procedure using CDTA as that previously reported for the rabbit skeletal myofibrils (Morimoto, S. & Ohtsuki, I. (1987) J. Biochem. 101, 291-301), and the effects of substitution of troponin C in cardiac myofibrils with rabbit skeletal troponin C or bovine brain calmodulin were examined. While the ATPase activity of intact cardiac myofibrils or cardiac troponin C-reconstituted cardiac myofibrils was activated at only a little higher concentration of Sr2+ than Ca2+, the skeletal troponin C-substituted cardiac myofibrils, as well as intact rabbit skeletal myofibrils, required more than 10 times higher concentration of Sr2+ than Ca2+ for activation of the myofibrillar ATPase activity. However, the concentrations of Ca2+ and Sr2+ required for the activation of the ATPase activity of the skeletal troponin C-substituted cardiac myofibrils were both about 5 times higher than those of intact skeletal myofibrils. The skeletal troponin C-substituted cardiac myofibrils, as well as intact skeletal myofibrils, also showed higher cooperativity in the Ca2+-activation of the ATPase activity than intact or cardiac troponin C-reconstituted cardiac myofibrils. The ATPase activity of calmodulin-substituted cardiac myofibrils was activated at a several times lower concentration of Ca2+ or Sr2+ than that of calmodulin-substituted skeletal myofibrils, while the ratios of the concentration of Sr2+ to Ca2+ required for activation were almost the same in both cases.(ABSTRACT TRUNCATED AT 250 WORDS)
Morimoto
S
S
Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka.
Ohtsuki
I
I
D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology*; D002614:Chelating Agents / Q000494:pharmacology; D004492:Edetic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D007700:Kinetics; D009206:Myocardium / Q000201:enzymology*; D009210:Myofibrils / Q000201:enzymology*; D011817:Rabbits; D013324:Strontium / Q000494:pharmacology*; D013552:Swine; D014336:Troponin / Q000494:pharmacology / Q000502:physiology*; D019209:Troponin C
D002147:Calmodulin; D002614:Chelating Agents; D014336:Troponin; D019209:Troponin C; C005390:CDTA; D004492:Edetic Acid; D000252:Calcium-Transporting ATPases; D013324:Strontium