Williams G J, Collins S, Muir J R, Stephens M R
Recent Adv Stud Cardiac Struct Metab. 1975;5:273-80.
The ability of cardiac myosin, actomyosin, and myofibrils to hydrolyze ATP has been studied at varying hydrogen and calcium ion concentrations. The ATPase activity of dog cardiac myofibrils was measured over the pH range of 6.5-7.4, as the calcium ion concentration was varied from 0-1.5 X 10(-4) M. The ATPase of these myofibrils, and of rabbit cardiac myosin and actomyosin was also measured in the absence of ionic calcium over the pH range 6-9. The Km of MgATP of cardiac myofibrils was studied over the pH range 6.5-7.4. In the absence of calcium ions, myofibrillar, myosin, and actomyosin ATPase activities are maximal at pH 8.0. At any given calcium ion concentration, the myofibrillar ATPase is depressed by lowering pH. The results suggest that the influence of hydrogen ions on the ability of myofibrils to hydrolyze ATP is complex, and may not only be the result of a simple competition between hydrogen and calcium ions for binding sites on troponin.
已在不同的氢离子和钙离子浓度下研究了心肌肌球蛋白、肌动球蛋白和肌原纤维水解ATP的能力。在钙离子浓度从0至1.5×10⁻⁴M变化时，测定了犬心肌肌原纤维在pH 6.5 - 7.4范围内的ATP酶活性。还在无离子钙存在的情况下，于pH 6 - 9范围内测定了这些肌原纤维以及兔心肌肌球蛋白和肌动球蛋白的ATP酶活性。在pH 6.5 - 7.4范围内研究了心肌肌原纤维MgATP的Km值。在无钙离子时，肌原纤维、肌球蛋白和肌动球蛋白的ATP酶活性在pH 8.0时最大。在任何给定的钙离子浓度下，降低pH会抑制肌原纤维ATP酶。结果表明，氢离子对肌原纤维水解ATP能力的影响是复杂的，可能不仅仅是氢离子和钙离子在肌钙蛋白结合位点上简单竞争的结果。
