Crooks R, Cooke R
J Gen Physiol. 1977 Jan;69(1):37-55. doi: 10.1085/jgp.69.1.37.
Threads of contractile proteins were formed via extrusion and their isometric tensions and isotonic contraction velocities were measured. We obtained reproducible data by using a new and sensitive tensiometer. The force-velocity curves of actomyosin threads were similar to those of muscle, with isometric tensions of the order of 10g/cm2 and maximum contraction velocites of the order of 10(-2) lengths/s. The data could be fitted by Hill's equation. Addition of tropomyosin and troponin to the threads increased isometric tension and maximum contraction velocity. Threads which contained troponin and tropomyosin required Ca++ for contraction and the dependence of their isometric tension on the level of free Ca++ was like that of muscle. The dependence of tension or of contraction velocity upon temperature or upon ionic strength is similar for actomyosin threads and muscle fibers. In contrast, the dependence of most parameters which are characteristic of the actomyosin interaction in solution (or suspension) upon these variables is not similar to the dependence of the muscle fiber parameters. The conclusion we have drawn from these results is that the mechanism of tension generation in the threads is similar to the mechanism that exists in muscle. Because the protein composition of the thread system can be manipulated readily and because the tensions and velocities of the threads can be related directly to the physiological parameters of muscle fibers, the threads provide a powerful method for studying contractile proteins.
通过挤压形成收缩蛋白丝，并测量其等长张力和等张收缩速度。我们使用一种新型灵敏张力计获得了可重复的数据。肌动球蛋白丝的力-速度曲线与肌肉的相似，等长张力约为10g/cm2，最大收缩速度约为10(-2)长度/秒。这些数据可用希尔方程拟合。向丝中添加原肌球蛋白和肌钙蛋白可增加等长张力和最大收缩速度。含有肌钙蛋白和原肌球蛋白的丝收缩需要Ca++，其等长张力对游离Ca++水平的依赖性与肌肉相似。肌动球蛋白丝和肌纤维的张力或收缩速度对温度或离子强度的依赖性相似。相比之下，溶液（或悬浮液）中肌动球蛋白相互作用的大多数特征参数对这些变量的依赖性与肌纤维参数的依赖性不同。我们从这些结果中得出的结论是，丝中张力产生的机制与肌肉中存在的机制相似。由于丝系统的蛋白质组成易于操控，且丝的张力和速度可直接与肌纤维的生理参数相关，因此丝为研究收缩蛋白提供了一种有力的方法。
