Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA.
Biophys J. 1999 Nov;77(5):2657-64. doi: 10.1016/S0006-3495(99)77100-6.
Observed effects of inorganic phosphate (P(i)) on active isometric muscle may provide the answer to one of the fundamental questions in muscle biophysics: how are the free energies of the chemical species in the myosin-catalyzed ATP hydrolysis (ATPase) reaction coupled to muscle force? Pate and Cooke (1989. Pflugers Arch. 414:73-81) showed that active, isometric muscle force varies logarithmically with [P(i)]. Here, by simultaneously measuring electron paramagnetic resonance and the force of spin-labeled muscle fibers, we show that, in active, isometric muscle, the fraction of myosin heads in any given biochemical state is independent of both [P(i)] and force. These direct observations of mechanochemical coupling in muscle are immediately described by a muscle equation of state containing muscle force as a state variable. These results challenge the conventional assumption mechanochemical coupling is localized to individual myosin heads in muscle.
观察到的无机磷酸盐 (P(i)) 对活跃的等长肌肉的影响可能为肌肉生物物理学中的一个基本问题提供答案：肌球蛋白催化的 ATP 水解 (ATPase) 反应中的化学物质的自由能如何与肌肉力量相耦合？Pate 和 Cooke（1989. Pflugers Arch. 414:73-81）表明，活跃的等长肌肉力量与 [P(i)] 呈对数关系。在这里，通过同时测量电子顺磁共振和带自旋标记的肌肉纤维的力，我们表明，在活跃的等长肌肉中，任何给定生化状态的肌球蛋白头部的分数与 [P(i)] 和力无关。这些对肌肉中机械化学耦联的直接观察可以通过包含肌肉力作为状态变量的肌肉状态方程来立即描述。这些结果挑战了机械化学耦联局限于肌肉中单个肌球蛋白头部的传统假设。
