Isotope Effects and Temperature Dependences in the Action of the Glucose Dehydrogenase of the Mesophilic Bacterium Bacillus megaterium.
Isotope Effects and Temperature Dependences in the Action of the Glucose Dehydrogenase of the Mesophilic Bacterium Bacillus megaterium.
复制标题
嗜温细菌巨大芽孢杆菌葡萄糖脱氢酶作用中的同位素效应和温度依赖性。
DOI：
10.1002/poc.3166
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发表时间：
2013
影响因子：
1.8
通讯作者：
Schowen,RichardL
中科院分区：
文献类型：
--
作者：
Anandarajah,Kandiah;Schowen,KBarbara;Schowen,RichardL
嗜温细菌巨大芽孢杆菌（最佳生长温度约为35 °C）的葡萄糖脱氢酶在其催化1-h-D-葡萄糖和1-d-D-葡萄糖的β-端基异构体通过氢化物转移至NAD+的氧化过程中（速率常数kcat/KMβ）显示出25至55 °C的非线性艾林温度依赖性。300 K附近的断裂将高T区域与低T区域分开。在高温区，在相当大的实验误差内，同位素活化能等于零。在低T区，同位素底物的活化能大致相等，但不为零。采用Eyring图作为有效线性的替代处理产生具有H底物（26 kJ/mol）比D底物（21 kJ/mol）更大的不寻常特征的活化谱。通过对H-底物更正的熵来补偿同位素效应，然后再现同位素效应。在先前关于NADP+氧化同一对同位素葡萄糖底物的工作中，嗜热古菌嗜酸热浆菌的葡萄糖脱氢酶的催化作用导致了温度依赖性，其特征在于由温和的热转变分离的高T区域和低T区域。对这两种情况的机制解释的尝试性方法依赖于以酶的构型搜索为特征的隧道状态模型，然后是氢转移隧道，尽管解释也可以基于简单的过渡态稳定而没有隧道来构建。版权所有© 2013约翰威利父子有限公司.
The glucose dehydrogenase of the mesophilic bacteriumBacillus megaterium(optimal growth around 35 °C) exhibits non‐linear Eyring temperature dependences from 25 to 55 °C in its catalysis of the oxidation by hydride‐transfer to NAD+of the β‐anomers of 1‐h‐D‐glucose and 1‐d‐D‐glucose (rate constant kcat/KMβ). A break around 300 K separates a high‐T region from a low‐T region. In the high‐T region, isotopic enthalpies of activation within a considerable experimental error are equal to zero. In the low‐T region, the enthalpies of activation are roughly equal for the isotopic substrates but are different from zero. An alternative treatment with Eyring plots taken as effectively linear produces enthalpies of activation having the unusual feature of being larger for the H‐substrate (26 kJ/mol) than for the D‐substrate (21 kJ/mol). Compensation of the enthalpic effect by a more positive entropy for the H‐substrate then reproduces the isotope effects. In previous work on oxidation by NADP+of the same pair of isotopic glucose substrates, catalysis by the glucose dehydrogenase ofThermoplasma acidophilum, a thermophilic archaeon, led to temperature dependences characterized by a high‐T region and a low‐T region separated by a gentle thermal transition. Tentative approaches to a mechanistic interpretation of both cases rely on models featuring configurational searches of the enzyme for tunneling states, followed by hydrogen‐transfer tunneling, although explanations can be constructed also on the basis of simple transition‐state stabilization without tunnelling. Copyright © 2013 John Wiley & Sons, Ltd.