The role of quantum effects in proton transfer reactions in enzymes: quantum tunneling in a noisy environment?
The role of quantum effects in proton transfer reactions in enzymes: quantum tunneling in a noisy environment?
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DOI：
10.1088/1367-2630/12/5/055002
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发表时间：
2010-05-21
影响因子：
3.3
通讯作者：
McKenzie, Ross H.
中科院分区：
文献类型：
--
作者：
Bothma, Jacques P.;Gilmore, Joel B.;McKenzie, Ross H.
我们考虑量子效应在酶催化反应中类氢物种转移中的作用。这篇评论是刺激的索赔，所观察到的幅度和温度依赖性的动力学同位素效应（KIE）意味着量子隧穿低于与过渡态相关的能量势垒显着提高了许多酶的反应速率。我们回顾了路径积分方法和Caldeira-Leggett模型，它提供了一个通用的框架来描述和理解在非零温度下与噪声环境相互作用的量子系统中的隧穿。在这里，量子系统是酶的活性位点，环境是周围的蛋白质和水。低于势垒的温度仅发生在温度T-0以下，温度T-0由势垒顶部附近的势能表面的曲率决定。我们认为，对于大多数酶来说，这个温度低于室温。我们审查典型的Caldeira-Leggett哈密顿量中的参数值，包括频率相关的摩擦和噪声，由于环境。对于物理上合理的参数，我们表明，量子过渡态理论给出了定量描述的温度依赖性和幅度的KIE的两类酶，已被声称表现出量子隧穿的签名。唯一的量子效应是与过渡态相关的，包括势垒顶部的反射和势垒下方的隧穿。我们确定，由于环境的摩擦和噪音是微弱的，只有轻微的修改反应速率。此外，在室温下，对于典型的能量势垒，频率远小于1000 cm（-1）的环境波动对反应速率的量子校正没有显著影响。这主要是因为与质子转移动力学相关的时间尺度比与蛋白质和溶剂相关的低频噪声快。
We consider the role of quantum effects in the transfer of hydrogen-like species in enzyme-catalyzed reactions. This review is stimulated by claims that the observed magnitude and temperature dependence of kinetic isotope effects (KIEs) implies that quantum tunneling below the energy barrier associated with the transition state significantly enhances the reaction rate in many enzymes. We review the path integral approach and the Caldeira-Leggett model, which provides a general framework to describe and understand tunneling in a quantum system that interacts with a noisy environment at nonzero temperature. Here the quantum system is the active site of the enzyme, and the environment is the surrounding protein and water. Tunneling well below the barrier only occurs for temperatures less than a temperature T-0, which is determined by the curvature of the potential energy surface near the top of the barrier. We argue that for most enzymes this temperature is less than room temperature. We review typical values for the parameters in the Caldeira-Leggett Hamiltonian, including the frequency-dependent friction and noise due to the environment. For physically reasonable parameters, we show that quantum transition state theory gives a quantitative description of the temperature dependence and magnitude of KIEs for two classes of enzymes that have been claimed to exhibit signatures of quantum tunneling. The only quantum effects are those associated with the transition state, both reflection at the barrier top and tunneling just below the barrier. We establish that the friction and noise due to the environment are weak and only slightly modify the reaction rate. Furthermore, at room temperature and for typical energy barriers environmental fluctuations with frequencies much less than 1000 cm(-1) do not have a significant effect on quantum corrections to the reaction rate. This is essentially because the time scales associated with the dynamics of proton transfer are faster than much of the low-frequency noise associated with the protein and solvent.