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Small Temperature Dependence of the Kinetic Isotope Effect for the Hydride Transfer Reaction Catalyzed by Escherichia coli Dihydrofolate Reductase

机译:大肠杆菌二氢叶酸还原酶催化的氢化物转移反应动力学同位素效应的温度依赖性小

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摘要

The H/D primary kinetic isotope effect (KIE) for the hydride transfer reaction catalyzed by Escherichia coli dihydrofolate reductase (ecDHFR) is calculated as a function of temperature employing ensemble-averaged variational transition-state theory with multidimensional tunneling. The calculated KIEs display only a small temperature dependence over the temperature range of 5 to 45 °C. We identify two key features that contribute to canceling most of the temperature dependence of the KIE that would be expected on the basis of simpler models. Related issues such as the isotope effects on Arrhenius preexponential factors, large differences between free energies of activation and Arrhenius activation energy, and fluctuations of effective barriers are also discussed.
机译:利用集合平均变分过渡态理论和多维隧穿,计算大肠杆菌二氢叶酸还原酶(ecDHFR)催化的氢化物转移反应的H / D初级动力学同位素效应(KIE)。计算得出的KIE在5至45°C的温度范围内仅显示出很小的温度依赖性。我们确定了两个关键特征,这些特征有助于消除KIE的大部分温度依赖性,而这在简单模型的基础上是可以预期的。还讨论了同位素对Arrhenius指数因子的影响,活化自由能与Arrhenius活化能之间的巨大差异以及有效势垒的波动等相关问题。

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