Stepkowski D, Orlova A A, Moos C
Department of Cellular Biochemistry, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warszawa.
Biochem J. 1994 May 15;300 ( Pt 1)(Pt 1):153-8. doi: 10.1042/bj3000153.
The actin activated ATPase of myosin at low ionic strength shows a complex dependence on actin concentration, in contrast with the simple hyperbolic actin activation kinetics of heavy meromyosin and subfragment-1. To investigate how the aggregation of myosin influences the actomyosin ATPase kinetics, we have studied the actin-activated ATPase of mixed filaments in which the myosin molecules are separated from each other by copolymerization with myosin rod. Electron microscopy of copolymer filaments, alone and bound to actin, indicates that the myosin heads are distributed randomly along the co-polymer filaments. The actin-activated ATPase of myosin decreases with increasing rod, approaching a plateau of about 30% of the control at a rod/myosin molar ratio of 4:1. The decrease in ATPase persists even at Vmax, the extrapolated limit at infinite actin, indicating that it is not due merely to the loss of cooperative actin binding. Furthermore, the actin dependence of the ATPase still shows a biphasic character like that of control myosin, even at rod/myosin ratio of 12:1, so this complexity is not probably due solely to the structural proximity of myosin molecules, but may involve a non-equivalence of myosin heads or myosin molecules in the filament environment.
在低离子强度下，肌球蛋白的肌动蛋白激活的ATP酶对肌动蛋白浓度表现出复杂的依赖性，这与重酶解肌球蛋白和亚片段-1简单的双曲线型肌动蛋白激活动力学形成对比。为了研究肌球蛋白的聚集如何影响肌动球蛋白ATP酶动力学，我们研究了混合丝的肌动蛋白激活的ATP酶，其中肌球蛋白分子通过与肌球蛋白杆共聚而彼此分离。单独的以及与肌动蛋白结合的共聚物丝的电子显微镜观察表明，肌球蛋白头部沿共聚物丝随机分布。肌球蛋白的肌动蛋白激活的ATP酶随着杆的增加而降低，在杆/肌球蛋白摩尔比为4:1时接近对照的约30%的平稳期。即使在Vmax（无限肌动蛋白时的外推极限）下，ATP酶的降低仍然持续，这表明它不仅仅是由于协同肌动蛋白结合的丧失。此外，即使在杆/肌球蛋白比为12:1时，ATP酶对肌动蛋白的依赖性仍然表现出与对照肌球蛋白类似的双相特征，因此这种复杂性可能不仅仅是由于肌球蛋白分子的结构接近，而是可能涉及丝环境中肌球蛋白头部或肌球蛋白分子的不等效性。
