Castellani L, Cohen C
Proc Natl Acad Sci U S A. 1987 Jun;84(12):4058-62. doi: 10.1073/pnas.84.12.4058.
Myosin from a molluscan catch muscle is unusual in being phosphorylated in the rod by an endogenous heavy chain kinase. The overall structure of the molecule resembles that of other muscle myosins, although the tail is somewhat longer (approximately equal to 1700 A). At low ionic strength the unphosphorylated molecules associate in filaments that display a striking axial repeat of 145 A. Phosphorylation of the rod enhances myosin solubility in the range of NaCl between 0.05 and 0.15 M. Depending on the ionic strength and the counterions present, the soluble species corresponds to an antiparallel folded dimer (15 S) or to a folded monomer (10 S). Unphosphorylated myosin can also be partially solubilized into folded monomers by addition of ATP in 0.15 M NaCl. A similar molecular folding has also been observed in smooth muscle and nonmuscle myosins that depends, however, on the state of phosphorylation of the light chains in the myosin head. We discuss these results in relation to possible mechanisms for control of catch contraction.
来自软体动物捕捉肌的肌球蛋白不同寻常，其杆状部分会被一种内源性重链激酶磷酸化。该分子的整体结构与其他肌肉肌球蛋白相似，不过其尾部稍长一些（约1700埃）。在低离子强度下，未磷酸化的分子会组装成细丝，呈现出145埃的显著轴向重复。杆状部分的磷酸化增强了肌球蛋白在0.05至0.15M氯化钠范围内的溶解度。根据离子强度和存在的抗衡离子，可溶形式对应于反平行折叠二聚体（15S）或折叠单体（10S）。在0.15M氯化钠中添加ATP，未磷酸化的肌球蛋白也可部分溶解为折叠单体。在平滑肌和非肌肉肌球蛋白中也观察到了类似的分子折叠，不过这取决于肌球蛋白头部轻链的磷酸化状态。我们结合控制捕捉收缩的可能机制来讨论这些结果。
