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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >A dominant homolytic O-Cl bond cleavage with low-spin triplet-state Fe(IV)=O formed is revealed in the mechanism of heme-dependent chlorite dismutase
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A dominant homolytic O-Cl bond cleavage with low-spin triplet-state Fe(IV)=O formed is revealed in the mechanism of heme-dependent chlorite dismutase

机译：低血红素依赖的亚氯酸盐歧化酶的机理揭示了低速三重态Fe（IV）= O形成的显性均质O-Cl键裂解。

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Chlorite dismutase (Cld) is a heme-dependent enzyme that catalyzes the decomposition of toxic chlorite (ClO_2 -) into innocuous chloride and O_2. In this paper, using the hybrid B3LYP density functional theory (DFT) method including dispersion interactions, the Cld reaction mechanism has been studied with a chemical model constructed on the X-ray crystal structure. The calculations indicate that the reaction proceeds along a stepwise pathway in the doublet state, i.e. a homolytic O-Cl bond cleavage of the substrate leading to an O-Fe(heme) species and a ClO? radical, followed by a rebinding O-O bond formation between them. The O-Fe(heme) species is demonstrated to be a low-spin triplet-state Fe(IV)=O diradicaloid. A low-spin singlet-state Fe(IV)=O is much less stable than the former, with an energy difference of 9.2 kcal mol~(-1). The O-Cl bond cleavage is rate-limiting with a barrier of 10.6 kcal mol~(-1), in good agreement with the experimental reaction rate of 2.0 × 10~5 s~(-1). Furthermore, a heterolytic O-Cl bond dissociation in the initial step is shown to be unreachable, which ensures the high efficiency of the Cld enzyme by avoiding the generation of chlorate byproduct observed in the reactions of synthetic Fe porphyrins. Also, the pathways in the quartet and sextet states are unfavorable for the Cld reaction. The present results reveal a detailed mechanism III (defined in the text) including an interesting di-radical intermediate composed of a low-spin triplet-state Fe(IV)=O and a ClO? radical. Compared to a competitive heterolytic Cl-O cleavage in synthetic Fe porphyrins, the revelation of the domination of homolysis in Cld indicates not only the high efficiency of enzyme, but also the sensitivity of a heme and the significance of the enzymatic active-site surroundings (the His170 and Arg183 residues in the present case), which gives more insights into heme chemistry.
机译：亚氯酸盐歧化酶（Cld）是一种血红素依赖性酶，可催化有毒亚氯酸盐（ClO_2-）分解为无害的氯化物和O_2。本文采用包含色散相互作用的混合B3LYP密度泛函理论（DFT）方法，利用在X射线晶体结构上建立的化学模型研究了Cld反应机理。计算表明，反应在双峰态下沿着逐步途径进行，即底物的均相O-Cl键裂解导致O-Fe（血红素）和ClO2的分解。自由基，然后在它们之间重新结合形成O-O键。 O-Fe（血红素）物种被证明是低自旋三重态Fe（IV）= O diradicaloid。低自旋单重态Fe（IV）= O的稳定性差得多，能量差为9.2 kcal mol〜（-1）。 O-Cl键的裂解是有速率限制的，其势垒为10.6 kcal mol〜（-1），与实验反应速率2.0×10〜5 s〜（-1）吻合良好。此外，最初步骤中的杂化O-Cl键解离是无法实现的，通过避免在合成铁卟啉反应中观察到氯酸盐副产物的生成，确保了Cld酶的高效。同样，四重态和六重态的途径对于Cld反应也是不利的。目前的结果揭示了详细的机理Ⅲ（在本文中定义），它包括由低旋转三重态Fe（Ⅳ）＝ O和ClO 2组成的有趣的双自由基中间体。激进。与合成Fe卟啉中竞争性的杂合Cl-O裂解相比，Cld中均质优势的揭示不仅表明酶的高效率，而且还表明血红素的敏感性以及酶促活性位点环境的重要性（ （本案例中的His170和Arg183残基），可提供有关血红素化学的更多见解。

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