Reactions of the diiron(IV) intermediate Q in soluble methane monooxygenase with fluoromethanes

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• 作者：Laurance G. Beauvais and Stephen J. Lippard
• 关键词：Soluble methane monooxygenase ; Hydroxylase ; Fluorocarbon oxidation ; Dioxygen activation ; Enzyme kinetics
• 刊名：Biochemical and Biophysical Research Communications
• 出版年：2005
• 出版时间：2005
• 年：2005
• 卷：338
• 期：1
• 页码：262-266
• 全文大小：206 K

文摘

Soluble methane monooxygenases utilize a carboxylate-bridged diiron center and dioxygen to convert methane to methanol. A diiron(IV) oxo intermediate Q is the active species for this process. Alternative substrates and theoretical studies can help elucidate the mechanism. Experimental results for reactions with derivatized methanes were previously modeled by a combination of quantum mechanical/molecular mechanical techniques and the model was extended to predict the relative reactivity of fluoromethane. We therefore studied reactions of Q with CF_nH_4−n (n = 1–3) to test the prediction. The kinetics of single-turnover reactions of Q with these substrates were monitored by double-mixing stopped-flow optical spectroscopy. For fluoro- and difluoromethane, conversion to the alcohols occurred with second-order rate constants less than that of methane, the values being 28,700 (CH₄) > 25,000 (CFH₃) > 9300 (CF₂H₂) M⁻¹ s⁻¹. KIE values for C–H versus C–D activation above the classical limit were observed, requiring modification of the theoretical predictions.