Ikebe M, Hinkins S, Hartshorne D J
Biochemistry. 1983 Sep 13;22(19):4580-7. doi: 10.1021/bi00288a036.
In the presence of adenosine 5'-triphosphate (ATP) and 1-10 mM MgCl2, the relative viscosity (eta rel) of dephosphorylated gizzard myosin is reduced markedly over a range of KCl from 0.35 to 0.15 M. Sedimentation patterns show that the decrease in eta rel is due to the conversion of the 6S to 10S forms of myosin. Under similar conditions, eta rel of phosphorylated myosin is not altered, and at 0.2 M KCl, the 10S form is not observed. In 1 and 2 mM MgCl2 and less than 0.2 M KCl, 10S can be formed from both phosphorylated myosin plus ATP and dephosphorylated myosin minus ATP. In the presence of ethylenediaminetetraacetic acid (EDTA), the decrease of eta rel and corresponding change in sedimentation pattern are independent of ATP and show only a dependence on KCl. Therefore, ATP and dephosphorylation are not obligatory for the 6S to 10S transition. In all instances, the 6S-10S transition of monomeric myosin is paralleled by an alteration of adenosine-5'-triphosphatase (ATPase) activity; i.e., the KCl dependence of the two processes is the same. Transition from 6S to 10S causes a decrease in Mg2+-and Ca2+-ATPase activity of myosin and an increase in K+-EDTA-ATPase activity. The relationship between myosin shape and the ATP dependence of Mg2+-ATPase activity also is consistent with this generalization. The phosphorylation dependence of the viscosity transition from 6S to 10S is not linear, and phosphorylation of both heads is required for the complete transition. In contrast, the ATP dependence of the transition is linear, and the binding of 2 mol of ATP/myosin is required for maximum effect.(ABSTRACT TRUNCATED AT 250 WORDS)
在存在腺苷 5'-三磷酸（ATP）和 1 - 10 mM 氯化镁（MgCl₂）的情况下，去磷酸化的肌胃肌球蛋白的相对粘度（ηrel）在 0.35 至 0.15 M 的氯化钾（KCl）浓度范围内显著降低。沉降模式表明，ηrel 的降低是由于肌球蛋白从 6S 形式转变为 10S 形式所致。在类似条件下，磷酸化肌球蛋白的 ηrel 未发生改变，并且在 0.2 M KCl 时，未观察到 10S 形式。在 1 和 2 mM MgCl₂以及低于 0.2 M KCl 的条件下，磷酸化肌球蛋白加 ATP 和去磷酸化肌球蛋白减 ATP 均可形成 10S。在存在乙二胺四乙酸（EDTA）的情况下，ηrel 的降低和沉降模式的相应变化与 ATP 无关，仅取决于 KCl。因此，ATP 和去磷酸化并非 6S 至 10S 转变所必需。在所有情况下，单体肌球蛋白的 6S - 10S 转变都伴随着腺苷 - 5'-三磷酸酶（ATPase）活性的改变；即，这两个过程对 KCl 的依赖性相同。从 6S 转变为 10S 会导致肌球蛋白的镁离子（Mg²⁺）和钙离子（Ca²⁺） - ATPase 活性降低，而钾离子（K⁺） - EDTA - ATPase 活性增加。肌球蛋白形状与 Mg²⁺ - ATPase 活性对 ATP 的依赖性之间的关系也与此概括一致。从 6S 到 10S 的粘度转变对磷酸化的依赖性并非线性，并且两个头部都磷酸化对于完全转变是必需的。相比之下，转变对 ATP 的依赖性是线性的，并且每分子肌球蛋白结合 2 摩尔 ATP 才能产生最大效应。（摘要截短至 250 字）
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