Dept. of Physics, University of Maine, 5709 Bennett Hall, Orono, ME 04469, USA.
Faraday Discuss. 2016 Dec 22;195:583-597. doi: 10.1039/c6fd00140h.
Molecular machines use external energy to drive transport, to do mechanical, osmotic, or electrical work on the environment, and to form structure. In this paper the fundamental difference between the design principles necessary for a molecular machine to use light or external modulation of thermodynamic parameters as an energy source vs. the design principle for using an exergonic chemical reaction as a fuel will be explored. The key difference is that for catalytically-driven motors microscopic reversibility must hold arbitrarily far from equilibrium. Applying the constraints of microscopic reversibility assures that a coarse grained model is consistent with an underlying model for motion on a single time-independent potential energy surface. In contrast, light-driven processes, and processes driven by external modulation of the thermodynamic parameters of a system cannot in general be described in terms of motion on a single time-independent potential energy surface, and the rate constants are not constrained by microscopic reversibility. The results presented here call into question the value of the so-called power stroke model as an explanation of the function of autonomous chemically-driven molecular machines such as are commonly found in biology.
分子机器利用外部能量来驱动运输，对环境进行力学、渗透或电力工作，并形成结构。在本文中，将探讨将光或外部调节热力学参数用作能源的分子机器所需的设计原则与将放能化学反应用作燃料的设计原则之间的根本区别。关键区别在于，对于催化驱动的马达，微观可逆性必须任意远离平衡。应用微观可逆性的约束条件可确保粗粒化模型与单个时间独立势能表面上的运动的基本模型一致。相比之下，光驱动过程和由系统热力学参数的外部调节驱动的过程通常不能用单个时间独立势能表面上的运动来描述，并且速率常数不受微观可逆性的限制。这里提出的结果质疑了所谓的力作用冲程模型作为对自主化学驱动分子机器（如在生物学中常见的）功能的解释的价值。
