IMPOSED OSCILLATIONS OF KINETIC BARRIERS CAN CAUSE AN ENZYME TO DRIVE A CHEMICAL-REACTION AWAY FROM EQUILIBRIUM
IMPOSED OSCILLATIONS OF KINETIC BARRIERS CAN CAUSE AN ENZYME TO DRIVE A CHEMICAL-REACTION AWAY FROM EQUILIBRIUM
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DOI：
10.1021/ja00077a001
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发表时间：
1993-12-01
影响因子：
15
通讯作者：
ROBERTSON, B
中科院分区：
文献类型：
--
作者：
ASTUMIAN, RD;ROBERTSON, B
化学反应的总吉布斯自由能变化（DELTAG）通常被称为反应的驱动力。DELTAG的符号定义了自发反应的方向，DELTAG = 0的条件定义了化学平衡点。这对于基元反应是严格正确的，基元反应沿着连接反应物和产物状态的反应坐标沿着只经过一个局部最大值（过渡态）。然而，在许多情况下，对于涉及一种或多种中间体的反应也是如此，特别是如果稳态中间体浓度非常小。在这里，我们表明，外部施加的振荡或波动可以驱动净化学反应远离平衡，只要整个反应的至少一个基本步骤的速率常数取决于波动参数。即使总DELTAG与扰动无关，这也是真的，并且即使中间态的浓度非常非常小（即，实验检测不到）。理解这一结果的关键是要认识到，施加的振荡确实对反应的中间态起作用。即使中间体的浓度非常小，这种功也可以在许多振荡周期中累积，导致净反应远离平衡的显著移动。我们的研究结果表明，添加酶（或任何催化剂）的化学反应最初在平衡（但暴露于振荡场）可能会导致反应进行远离平衡。这提供了一个明确的反例，说明在平衡的化学反应中加入少量催化剂不会导致反应偏离平衡。
The overall Gibbs free energy change (DELTAG) of a chemical reaction is often termed the driving force of the reaction. The sign of DELTAG defines the direction of spontaneous reaction, and the condition DELTAG = 0 defines the point of chemical equilibrium. This is strictly true for elementary reactions-reactions that pass through only one local maximum (the transition state) along the reaction coordinate connecting reactant and product states. However, under many circumstances it is also true for reactions that involve one or more intermediates, particularly if the steady state intermediate concentrations are very small. Here we show that externally imposed oscillations or fluctuations can drive a net chemical reaction away from equilibrium so long as the rate constants of at least one elementary step of the overall reaction depend on the fluctuating parameter. This is true even if the overall DELTAG is independent of the perturbation and it is also true even if the concentrations of the intermediate states are very, very small (i.e., experimentally undetectable). The key to understanding this result is to realize that the imposed oscillation does work on the intermediate states of the reaction. Even if the concentrations of the intermediates are very small, this work can accumulate over many cycles of oscillation, leading to a significant shift of the net reaction away from equilibrium. Our results demonstrate that the addition of an enzyme (or any catalyst) to a chemical reaction initially at equilibrium (but exposed to an oscillating field) may cause the reaction to proceed away from equilibrium. This provides an explicit counter example to the adage that the addition of a small amount of catalyst to a chemical reaction at equilibrium cannot cause the reaction to go away a from equilibrium.