Dynamic barriers and tunneling. New views of hydrogen transfer in enzyme reactions
Dynamic barriers and tunneling. New views of hydrogen transfer in enzyme reactions
复制标题
DOI：
10.1351/pac200375050601
复制
发表时间：
2003-01
影响因子：
1.8
通讯作者：
J. Klinman
中科院分区：
文献类型：
--
作者：
J. Klinman
氢转移过程被期望表现出可观的量子力学行为。对酶在其生理条件下的深入研究表明，几乎在所调查的每一个例子中都是如此。最初，隧道效应要么被视为隧道修正[参见Bell， The Tunnel Effect in Chemistry, Chapman & Hall, New York,(1980)]，要么被视为投机行为[Truhlar et al.， J. Chem.]。物理学报，2000,26(1):1 - 4。只要观察到的性质可以通过对过渡态理论的“修正”来解释，这种方法就很有效。然而，在过去的几年里，酶的行为已经被观察到如此偏离，以至于超出了过渡态理论。在大豆脂氧合酶的背景下讨论了这种现象。根据库兹涅佐夫（Kuznetsov）和乌尔斯特鲁普（Ullstrup）的理论，提出了一个环境耦合的氢隧穿模型。[j] .化学，77,689(1999)]，包括重原子重组（依赖于温度，很大程度上依赖于同位素），以及重原子门控（依赖于温度和同位素）。这种处理方法可以解释广泛的行为，并导致氢转移反应中动力学同位素效应起源的新观点。这些性质将酶的波动与氢转移反应坐标联系起来，使得氢转移的量子观点必然是催化的动态观点。
Abstract Hydrogen-transfer processes are expected to show appreciable quantum mechanical behavior. Intensive investigations of enzymes under their physiological conditions show this to be true in practically every example investigated. Initially, tunneling was treated either as a tunneling correction [cf. Bell, The Tunnel Effect in Chemistry, Chapman & Hall, New York, (l980)], or as corner-cutting [Truhlar et al., J. Chem. Phys. 100, 12771 (l996)]. This worked well as long as the observed properties could be explained by “corrections” to transition-state theory. However, over the past several years, enzymatic behaviors have been observed that are so deviant as to lie outside of transition-state theory. This phenomenon is discussed in the context of the enzyme, soybean lipoxygenase. An environmentally coupled hydrogen-tunneling model is presented that derives from the treatments of Kuznetsov and Ullstrup [Can. J. Chem. 77, 689 (l999)], and includes heavy-atom reorganization (temperature-dependent and largely isotope-independent), together with heavy-atom gating (temperature- and isotope-dependent). This treatment can explain a wide range of behaviors and leads to a new view of the origin of kinetic isotope effects in hydrogen-transfer reactions. These properties link enzyme fluctuations to the hydrogen-transfer reaction coordinate, making a quantum view of H-transfer necessarily a dynamic view of catalysis.