Irrelevance of the Power Stroke for the Directionality, Stopping Force, and Optimal Efficiency of Chemically Driven Molecular Machines
Irrelevance of the Power Stroke for the Directionality, Stopping Force, and Optimal Efficiency of Chemically Driven Molecular Machines
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DOI：
10.1016/j.bpj.2014.11.3459
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发表时间：
2015-01-20
影响因子：
3.4
通讯作者：
Astumian, R. Dean
中科院分区：
文献类型：
--
作者：
Astumian, R. Dean
化学驱动的分子步行者的简单模型表明，由分子储存并在称为动力冲程的构象变化期间释放的弹性能（即，做功冲程前和做功冲程后状态之间的自由能差）对于确定电动机的方向性、停止力和效率是无关的。此外，动力冲程的正向和反向速率常数之间（或实际上在所有速率常数之间）对外部施加的力的依赖性的分配对于确定电动机的方向性、停止力和效率是无关的。基于微观可逆性原理的论证表明，这一结果对所有化学驱动的分子机器都是普遍的，甚至更广泛地说，马达状态的相对能量在决定方向性、停止力或机器的最佳效率方面没有作用。相反，方向性，阻止力和最佳效率仅由状态之间的能量势垒的相对高度决定。分子构象--分子机器根据机器状态区分底物和产物的能力--对于确定化学-机械耦合的内在方向性和热力学比机器内部机械构象运动的细节重要得多。与化学驱动的结论相反，动力冲程对于光驱动分子机器的方向性和效率以及对于由热力学参数的外部调制驱动的分子机器是非常重要的。
A simple model for a chemically driven molecular walker shows that the elastic energy stored by the molecule and released during the conformational change known as the power-stroke (i.e., the free-energy difference between the pre- and post-power-stroke states) is irrelevant for determining the directionality, stopping force, and efficiency of the motor. Further, the apportionment of the dependence on the externally applied force between the forward and reverse rate constants of the power-stroke (or indeed among all rate constants) is irrelevant for determining the directionality, stopping force, and efficiency of the motor. Arguments based on the principle of microscopic reversibility demonstrate that this result is general for all chemically driven molecular machines, and even more broadly that the relative energies of the states of the motor have no role in determining the directionality, stopping force, or optimal efficiency of the machine. Instead, the directionality, stopping force, and optimal efficiency are determined solely by the relative heights of the energy barriers between the states. Molecular recognition-the ability of a molecular machine to discriminate between substrate and product depending on the state of the machine-is far more important for determining the intrinsic directionality and thermodynamics of chemo-mechanical coupling than are the details of the internal mechanical conformational motions of the machine. In contrast to the conclusions for chemical driving, a power-stroke is very important for the directionality and efficiency of light-driven molecular machines and for molecular machines driven by external modulation of thermodynamic parameters.