Smith D A, Geeves M A
Max-Planck Institute for Molecular Physiology, Dortmund, Germany.
Biophys J. 1995 Aug;69(2):524-37. doi: 10.1016/S0006-3495(95)79926-X.
The cross-bridge cycle for actin, S1 myosin, and nucleotides in solution is applied to the sliding filament model for fully activated striated muscle. The cycle has attached and rotated isomers of each actomyosin state. It is assumed that these forms have different zero-strain conformations with respect to the filament and that strain-free rate constants are the nominal solution values. Only one S1 unit of heavy meromyosin is considered. Transition-state theory is used to predict the strain dependences of S1 binding to actin, the force-generating transition to rotated states, and the release/binding of nucleotide and phosphate. We propose that ADP release and ATP binding are blocked by positive strain and phosphate release by negative strain. At large strains, rapid dissociation of S1 nucleotide from actin is expected when the compliant element of the cross-bridge is strained in either direction beyond its elastic limits. The dynamical behavior of this model of muscle contraction is discussed in general terms. Its computed steady-state properties are presented in an accompanying paper.
溶液中肌动蛋白、肌球蛋白S1和核苷酸的横桥循环应用于完全激活的横纹肌的滑动丝模型。该循环具有每个肌动球蛋白状态的附着和旋转异构体。假定这些形式相对于细丝具有不同的零应变构象，并且无应变速率常数为标称溶液值。仅考虑重酶解肌球蛋白的一个S1单位。采用过渡态理论预测S1与肌动蛋白结合的应变依赖性、向旋转状态的力产生转变以及核苷酸和磷酸盐的释放/结合。我们提出，正应变会阻止ADP释放和ATP结合，负应变会阻止磷酸盐释放。在大应变下，当横桥的柔顺元件在任一方向上应变超过其弹性极限时，预计S1核苷酸会从肌动蛋白上快速解离。本文对该肌肉收缩模型的动力学行为进行了一般性讨论。其计算得到的稳态特性在随附论文中给出。
