The combined molecular dynamics (MD) simulations and quantum mechanical/molecular mechanics (QM/MM) calculations have been performed to address the longstanding issue of the “dioxygen activation” by the nonheme diiron monooxygenase myo-inositol oxygenase (MIOX). MIOX utilizes a mixed-valence Fe2(III)Fe1(II) cluster for catalysis. It is well recognized that the Fe2(III) site is responsible for the substrate myo-inositol (MI) binding, while the Fe1(II) site is responsible for O₂ binding and activation. However, it is enigmatic how the O–O bond of oxygen is reductively cleaved in the absence of additional reductants. In this study, we demonstrate a spin-regulated inner-sphere electron-transfer mechanism that is involved in the catalytic reactions of MIOX. Because of the Pauli principle and exchange-enhanced reactivity, the spin-regulated inner-sphere electron transfer enables the formation of an unprecedented Fe2(III)Fe1(II)-peroxyhemiketal intermediate that is responsible for the reductive O–O cleavage. In contrast to Fe1(III)-mediated O–O cleavage in the Fe2(II)Fe1(III)-peroxyhemiketal intermediate proposed previously, our calculations demonstrate that the proton transfer-triggered Fe1–O cleavage in Fe2(III)Fe1(II)-peroxyhemiketal intermediate is the most favorable pathway, leading to MI-OOH intermediate and the Fe1(II) species. The following Fe1(II)-mediated O–O homolysis in MI-OOH generates the substrate radical and Fe(III)–OH species, during which the Fe1(IV)═O intermediate would be bypassed. Thus, our calculations show that both Fe sites are cooperately involved in O₂ activation in MIOX and such cooperation is well regulated by the spin-dependent inner-sphere electron transfer. These findings of O₂ activation by MIOX may have far-reaching implications on other related nonheme diiron monooxygenases.

中文翻译：

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自旋调节的内层电子转移可在非血红素二铁单加氧酶MIOX中实现有效的O-O键活化

已经进行了分子动力学（MD）模拟和量子力学/分子力学（QM / MM）的组合计算，以解决由非血红素二铁单加氧酶肌醇加氧酶（MIOX）引起的“双氧激活”的长期问题。MIOX利用混合价Fe2（III）Fe1（II）簇进行催化。众所周知，Fe2（III）位点负责底物肌醇（MI）的结合，而Fe1（II）位点负责O _{2的作用。}绑定和激活。然而，在没有其他还原剂的情况下，氧气的O-O键如何被还原裂解是个谜。在这项研究中，我们证明了自旋调节的内球电子转移机制参与MIOX的催化反应。由于泡利原理和交换增强的反应性，自旋调节的内球电子转移使得能够形成空前的Fe2（III）Fe1（II）-过氧半缩酮中间体，该中间体负责还原性O-O裂解。与先前提出的Fe2（II）Fe1（III）-过氧半水合物中间体中的Fe1（III）介导的O–O裂解相反，我们的计算表明，质子转移触发了Fe2（III）Fe1（II）的Fe1–O裂解。 ）-过氧半水酮中间体是最有利的途径，导致MI-OOH中间体和Fe1（II）物种。在MI-OOH中，以下Fe1（II）介导的O-O均相分解产生了底物自由基和Fe（III）-OH，在此期间将绕过Fe1（IV）intermediateO中间体。因此，我们的计算表明两个铁位点共同参与了OMIOX中的₂活化和这种合作受自旋依赖性内球电子转移的良好调控。MIOX激活O _2的这些发现可能对其他相关的非血红素二铁单加氧酶有深远的影响。