Reactions of the peroxo intermediate of soluble methane monooxygenase hydroxylase with ethers
Reactions of the peroxo intermediate of soluble methane monooxygenase hydroxylase with ethers
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DOI：
10.1021/ja050865i
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发表时间：
2005-05-25
影响因子：
15
通讯作者：
Lippard, SJ
中科院分区：
文献类型：
--
作者：
Beauvais, LG;Lippard, SJ
从荚膜甲基球菌 (Bath) 中分离出的可溶性甲烷单加氧酶 (sMMO) 利用羧酸桥联铁中心和双氧来催化甲烷转化为甲醇。先前的研究表明，称为 Q 的二（mu-oxo）二铁（IV）中间体负责对碳氢化合物的催化活性。此外，催化循环中Q形成之前的过氧二铁(III)中间体(H(peroxo))已被证明可以与丙烯反应，但其反应性尚未得到广泛研究。鉴于人们对金属酶中存在多种氧化剂的兴趣日益浓厚，对 H(peroxo) 的反应性进行了更详尽的研究。通过单混合和双混合停流光谱监测两种中间体与乙基乙烯基醚和乙醚的单周转反应动力学。对于这两种底物，与 Hperoxo 反应的速率常数大于与 Q 反应的速率常数。描述了用于解释瞬态动力学的分析模型，并成功用于拟合观察到的数据。通过温度依赖性研究确定了活化参数，并测量了与乙醚反应的动力学同位素效应。速率常数表明H(peroxo)是比Q更亲电子的氧化剂。我们提出Hperoxo通过双电子转移机制进行反应，而Q通过单电子转移步骤进行反应。
Soluble methane monooxygenase (sMMO) isolated from Methylococcus capsulatus (Bath) utilizes a carboxylate-bridged diiron center and dioxygen to catalyze the conversion of methane to methanol. Previous studies revealed that a di(mu-oxo)diiron(IV) intermediate termed Q is responsible for the catalytic activity with hydrocarbons. In addition, the peroxodiiron(III) intermediate (H(peroxo)) that precedes Q formation in the catalytic cycle has been demonstrated to react with propylene, but its reactivity has not been extensively investigated. Given the burgeoning interest in the existence of multiple oxidants in metalloenzymes, a more exhaustive study of the reactivity of H(peroxo) was undertaken. The kinetics of single turnover reactions of the two intermediates with ethyl vinyl ether and diethyl ether were monitored by single- and double-mixing stopped-flow optical spectroscopy. For both substrates, the rate constants for reaction with Hperoxo are greater than those for Q. An analytical model for explaining the transient kinetics is described and used successfully to fit the observed data. Activation parameters were determined through temperature-dependent studies, and the kinetic isotope effects for the reactions with diethyl ether were measured. The rate constants indicate that H(peroxo) is a more electrophilic oxidant than Q. We propose that Hperoxo reacts via two-electron transfer mechanisms, and that Q reacts by single-electron transfer steps.