Effect of Arg145Gly mutation in human cardiac troponin I on the ATPase activity of cardiac myofibrils |
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Authors: | Takahashi-Yanaga F Morimoto S Ohtsuki I |
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Institution: | Laboratory of Clinical Pharmacology, Department of Pharmacological Sciences, Graduate School of Medicine, Kyushu University, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. yanaga@clipharm.med.kyushu-u.ac. jp |
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Abstract: | In order to determine the functional consequences of the Arg145Gly mutation in troponin I found in familial hypertrophic cardiomyopathy, human cardiac troponin I and its mutant were expressed in Escherichia coli and purified, and then their effects on the ATPase activity of porcine cardiac myofibrillar preparations from which both troponins C and I had been depleted were examined. Both the wild-type and mutant troponin Is suppressed the ATPase activity of the troponin C.I-depleted myofibrils, but the maximum inhibition caused by mutant troponin I was weaker than that by wild-type troponin I. In the Ca(2)(+)-activation profile of the myofibrillar ATPase activity after reconstitution with both troponins I and C, the Ca(2)(+)-sensitivity with mutant troponin I was higher than that with wild-type troponin I, whereas the maximum level of the ATPase activity with mutant troponin I was lower than that with wild-type troponin I. These findings strongly suggest that the Arg145Gly mutation in human cardiac troponin I modulates the Ca(2)(+)-regulation of contraction by impairing the interaction of troponin I with both actin-tropomyosin and troponin C. |
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