Evidence for C-H cleavage by an iron-superoxide complex in the glycol cleavage reaction catalyzed by myo-inositol oxygenase
Evidence for C-H cleavage by an iron-superoxide complex in the glycol cleavage reaction catalyzed by myo-inositol oxygenase
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DOI：
10.1073/pnas.0508473103
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发表时间：
2006-04-18
影响因子：
11.1
通讯作者：
Bollinger, JM
中科院分区：
文献类型：
--
作者：
Xing, G;Diao, YH;Bollinger, JM
肌醇加氧酶（MIOX）激活混合价非血红素二铁（II/III）簇上的O-2，以通过四个电子将其环己-（1，2，3，4，5，6-己）-醇底物[肌醇（MI）]氧化为D-葡萄糖醛酸。以前曾提出过通过形式上的（superoxo）二铁（III/III）中间体从C-1中提取氢。使用氘标记的底物1，2，3，4，5，6-[H-2]（6）-lMI（D-6-MI），现在已允许对C-H-裂解中间体进行初步表征。MIOX-1，2，3，4，5，6-[H-2]（6）-MI络合物与O-2快速可逆反应形成中间体G，g =（2.05，1.98，1.90）EPR信号。菱形g-张量和观察到的超精细耦合到Fe-57的合理化（superoxo）二铁（III/III）结构与超氧化物的协调，以一个单一的铁。G衰变为H，即先前在与未标记底物的反应中检测到的中间体。该步骤与>= 5的动力学同位素效应相关，表明超氧化物水平复合物确实裂解MI的C-H（D）键。
myo-Inositol oxygenase (MIOX) activates O-2 at a mixed-valent nonheme diiron(II/III) cluster to effect oxidation of its cyclohexan-(1,2,3,4,5,6-hexa)-ol substrate [myo-inositol (MI)] by four electrons to D-glucuronate. Abstraction of hydrogen from C-1 by a formally (superoxo)diiron(III/III) intermediate was previously proposed. Use of deuterium-labeled substrate, 1,2,3,4,5,6-[H-2](6)-lMI (D-6-MI), has now permitted initial characterization of the C-H-cleaving intermediate. The MIOX-1,2,3,4,5,6-[H-2](6)-MI complex reacts rapidly and reversibly with O-2 to form an intermediate, G, with a g = (2.05, 1.98, 1.90) EPR signal. The rhombic g-tensor and observed hyper-fine coupling to Fe-57 are rationalized in terms of a (superoxo)diiron(III/III) structure with coordination of the superoxide to a single iron. G decays to H, the intermediate previously detected in the reaction with unlabeled substrate. This step is associated with a kinetic isotope effect of >= 5, showing that the superoxide-level complex does indeed cleave a C-H(D) bond of MI.