[The changes in Ca(2+)-sensitivity of rabbit skeletal myofibrillar ATPase activity under various conditions].
Effect of the composition of the reaction mixture on the Ca(2+)-sensitivity of myofibrillar ATPase of rabbit skeletal muscle was investigated. The Ca(2+)-concentrations necessary for the half maximum ATPase activation were 2.95 x 10(-6) M at 50 mM KCl, 4.37 x 10(-6) M at 90 mM KCl and 5.25 x 10(-6) M at 130 mM KCl. Thus the Ca(2+)-sensitivity was definitely lower at higher KCl concentrations. The Ca(2+)-sensitivity was about 2 times higher at pH 7.3 (pCa50 5.65) compared to the Ca(2+)-sensitivity at pH 6.8 (pCa50 5.36). The change in the Mg-ATP concentration between 0.5 mM and 3.5 mM, did not significantly affect the Ca(2+)-sensitivity of myofibrillar ATPase, but affected biphasically the maximum ATPase activity. These change in the Ca(2+)-sensitivity at various conditions is considered to be due mainly to the property of troponin C, the Ca(2+)-receptive protein of myofibrils.
Nakagawa
E
E
Department of Clinical Pharmacology, Faculty of Medicine Kyushu University, Fukuoka.
Nomura
S
S
Fukuyama
S
S
Shiraishi
F
F
Hatakenaka
M
M
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D009210:Myofibrils / Q000201:enzymology*; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D014336:Troponin / Q000378:metabolism; D019209:Troponin C
D014336:Troponin; D019209:Troponin C; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D002118:Calcium