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首页> 外文期刊>Metabolites >From Cycling Between Coupled Reactions to the Cross-Bridge Cycle: Mechanical Power Output as an Integral Part of Energy Metabolism
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From Cycling Between Coupled Reactions to the Cross-Bridge Cycle: Mechanical Power Output as an Integral Part of Energy Metabolism

机译：从耦合反应之间的循环到跨桥循环：机械功率输出是能量代谢的组成部分

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摘要

ATP delivery and its usage are achieved by cycling of respective intermediates through interconnected coupled reactions. At steady state, cycling between coupled reactions always occurs at zero resistance of the whole cycle without dissipation of free energy. The cross-bridge cycle can also be described by a system of coupled reactions: one energising reaction, which energises myosin heads by coupled ATP splitting, and one de-energising reaction, which transduces free energy from myosin heads to coupled actin movement. The whole cycle of myosin heads via cross-bridge formation and dissociation proceeds at zero resistance. Dissipation of free energy from coupled reactions occurs whenever the input potential overcomes the counteracting output potential. In addition, dissipation is produced by uncoupling. This is brought about by a load dependent shortening of the cross-bridge stroke to zero, which allows isometric force generation without mechanical power output. The occurrence of maximal efficiency is caused by uncoupling. Under coupled conditions, Hill’s equation (velocity as a function of load) is fulfilled. In addition, force and shortening velocity both depend on [Ca2+]. Muscular fatigue is triggered when ATP consumption overcomes ATP delivery. As a result, the substrate of the cycle, [MgATP2−], is reduced. This leads to a switch off of cycling and ATP consumption, so that a recovery of [ATP] is possible. In this way a potentially harmful, persistent low energy state of the cell can be avoided.
机译：ATP的传递及其用法是通过相互连接的偶联反应循环各个中间体而实现的。在稳态下，耦合反应之间的循环始终在整个循环的零电阻下发生，而不会耗散自由能。跨桥循环也可以用耦合反应系统来描述：一个激发反应，通过耦合ATP分裂为肌球蛋白头部提供能量;一个脱能反应，将来自肌球蛋白头部的自由能转化为肌动蛋白运动。通过跨桥形成和解离的肌球蛋白头的整个循环以零电阻进行。每当输入电势克服抵消输出电势时，就会发生偶合反应产生的自由能消散。另外，通过解耦产生耗散。这是由于与负载有关的跨桥行程缩短到零而导致的，这允许在没有机械动力输出的情况下产生等距力。最大效率的发生是由于解耦引起的。在耦合条件下，满足希尔方程（速度与载荷的关系）。另外，力和缩短速度都取决于[Ca 2 + ]。当ATP消耗量超过ATP输送量时，就会引发肌肉疲劳。结果，减少了循环的底物[MgATP 2-]。这会导致循环和ATP消耗关闭，从而可以恢复[ATP]。以此方式，可以避免电池的潜在有害的，持久的低能量状态。

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