Chantler P D
J Mol Biol. 1985 Feb 20;181(4):557-60. doi: 10.1016/0022-2836(85)90428-0.
Readdition of regulatory light chains to regulatory light chain denuded scallop myofibrils, in the presence of magnesium, results in a negatively co-operative restoration of calcium sensitivity as a function of regulatory light chain content. The form of the stoichiometry curves obtained in the presence of 10 mM-EDTA, by light chain removal from scallop myofibrils at various temperatures, are parabolic in shape, consistent with a random removal process. However, in the presence of EDTA at low temperatures, regulatory light chains are removed in a biphasic manner, indicating that the binding constants of the light chains for each myosin head are not equivalent under these conditions. It is shown here that as the temperature is raised, light chain removal by EDTA approaches that of a random process. The stoichiometry curves obtained in the presence of 10 mM-EDTA may therefore be seen as a composite of both a biphasic removal process (temperatures below 20 degrees C) and a random removal process (temperatures above 20 degrees C), there being a temperature-dependent switch in the myosin molecule between 17 and 23 degrees C that governs the mode of light chain removal. These results indicate that both myosin heads must contain light chains for calcium sensitivity and are consistent with our earlier proposals for head-head co-operativity within the scallop myosin molecule.
在镁存在的情况下，向去除调节性轻链的扇贝肌原纤维中重新添加调节性轻链，会导致钙敏感性随调节性轻链含量呈负协同恢复。在10 mM - EDTA存在下，通过在不同温度下从扇贝肌原纤维中去除轻链获得的化学计量曲线呈抛物线形状，这与随机去除过程一致。然而，在低温下EDTA存在时，调节性轻链以双相方式被去除，这表明在这些条件下轻链与每个肌球蛋白头部的结合常数并不相等。此处表明，随着温度升高，EDTA去除轻链的方式接近随机过程。因此，在10 mM - EDTA存在下获得的化学计量曲线可视为双相去除过程（温度低于20摄氏度）和随机去除过程（温度高于20摄氏度）的组合，在17至23摄氏度之间肌球蛋白分子存在一个温度依赖性开关，它控制着轻链的去除模式。这些结果表明，两个肌球蛋白头部都必须含有轻链才能具有钙敏感性，这与我们之前关于扇贝肌球蛋白分子内头部 - 头部协同作用的提议一致。
