Ventura-Clapier R, Vassort G
Pflugers Arch. 1985 May;404(2):157-61. doi: 10.1007/BF00585412.
In the absence of creatine phosphate, MgATP produced relaxation of rigor tension in chemically-skinned right papillary muscles of the rat, the half maximal effect being obtained at 1.8 mM MgATP. In the presence of 12 mM creatine phosphate and 250 microM ADP, a decrease in MgATP concentration even to 10(-9) M never induced rigor tension. At a very low MgATP concentration (10(-6) M), the half maximal relaxing effect was obtained with 2 mM creatine phosphate, a value close to the Km of isolated MM-creatine kinase for this substrate, or with 14 microM MgADP, a value 5 times lower than the reported Km. An exogenous MgATP regenerating system (phosphoenol pyruvate + pyruvate kinase) was not able to fully relax the fibres. When MM-creatine kinase was inhibited by fluorodinitrobenzene, the dependency of rigor tension on MgATP became the same as it was without creatine phosphate. After washing out the fluorodinitrobenzene the addition of exogenous MM-creatine kinase for half an hour fully relaxed rigor tension; moreover, this effect persisted even after prolonged washout. These results show that endogenous MM-creatine kinase is able to ensure maximal efficiency of myosin ATPase by producing a localized high MgATP/MgADP ratio; they also suggest the existence of rapidly exchangeable binding sites for MM-creatine kinase in cardiac myofibrils.
在没有磷酸肌酸的情况下，MgATP可使大鼠化学去表皮右乳头肌的强直张力松弛，在1.8 mM MgATP时可获得半数最大效应。在存在12 mM磷酸肌酸和250 μM ADP的情况下，即使将MgATP浓度降至10⁻⁹ M也不会诱导强直张力。在非常低的MgATP浓度（10⁻⁶ M）下，2 mM磷酸肌酸可获得半数最大松弛效应，该值接近分离的MM-肌酸激酶对该底物的Km值，或者14 μM MgADP也可获得该效应，该值比报道的Km值低5倍。外源性MgATP再生系统（磷酸烯醇丙酮酸+丙酮酸激酶）不能使纤维完全松弛。当MM-肌酸激酶被氟二硝基苯抑制时，强直张力对MgATP的依赖性变得与没有磷酸肌酸时相同。洗去氟二硝基苯后，添加外源性MM-肌酸激酶半小时可使强直张力完全松弛；此外，即使长时间冲洗后该效应仍持续存在。这些结果表明，内源性MM-肌酸激酶能够通过产生局部高MgATP/MgADP比值来确保肌球蛋白ATP酶的最大效率；它们还表明心肌原纤维中存在MM-肌酸激酶的快速可交换结合位点。
