H and other transfers in enzymes and in solution: Theory and computations, a unified view. 2. Applications to experiment and computations
H and other transfers in enzymes and in solution: Theory and computations, a unified view. 2. Applications to experiment and computations
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DOI：
10.1021/jp071589s
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发表时间：
2007-06-21
影响因子：
3.3
通讯作者：
Marcus, R. A.
中科院分区：
文献类型：
--
作者：
Marcus, R. A.
讨论了第一部分中获得的关于结合反应物之间一步酶促反应的自由能势垒的方程。该速率以 lambda(o)（蛋白质重组能）、Delta G 度（H 转移步骤的标准反应自由能）、键断裂/成键项、w（功项）和 H 传输特性表示。在有利的情况下，通过发生最大氘动力学同位素效应的 Delta G 度，可以通过实验区分断键/成键和蛋白质耦合的两种替代近似。讨论了对数速率与 Delta G 度的关系图以及 Delta S* 和 Delta S 度等属性。在生理条件下操作的野生型酶的动力学同位素效应的弱或零 T 依赖性被解释为消失（或同位素不敏感）w加上从最低 H 状态的转移。讨论了静态和动态蛋白质的灵活性。虽然电子转移可用的许多相关性不适用于酶中的氢转移，但实验、计算和分析方法的结合可以帮助评估本方程的实用性并建议进一步的实验和计算。在文献中，蛋白质重组能 lambda(o) 是从使用非绝热电子态的扩展价键形式获得的。建议使用键距差坐标来提取它的方法。结果可能会在两种方法之间架起一座桥梁。
Equations obtained in part I for the free-energy barrier to one-step enzymatic reactions between bound reactants are discussed. The rate is expressed in terms of lambda(o) (protein reorganization energy), Delta G degrees (standard free energy of reaction of the H-transfer step), bond breaking/bond forming term, w (work terms), and H-transmission property. Two alternative approximations for the coupling of the bond breaking/bond forming and protein are distinguished experimentally in favorable cases by the Delta G degrees where the maximum deuterium kinetic isotope effect occurs. Plots of log rate versus Delta G degrees and properties such as Delta S* and Delta S degrees are discussed. The weak or zero T-dependence of the kinetic isotope effect for wild-type enzymes operating under physiological conditions is interpreted in terms of vanishing (or isotopically insensitive) w plus transfer from the lowest H-state. Static and dynamic protein flexibility is discussed. While the many correlations accessible for electron transfers are not available for H-transfers in enzymes, a combination of experiment, computation, and analytical approaches can assist in evaluating the utility of the present equations and in suggesting further experiments and computations. A protein reorganization energy lambda(o) is obtained in the literature from the extended valence bond formalism where diabatic electronic states are used. A method is suggested for extracting it when instead a bond distance difference coordinate is used. The results may provide a bridge between the two approaches.