The present work is another part of our investigation on the pathway of dissimilatory sulfate reduction and covers a theoretical study on the reaction catalyzed by dissimilatory sulfite reductase (dSIR). dSIR is the terminal enzyme involved in this metabolic pathway, which uses the siroheme‐[4Fe4S] cofactor for six‐electron reduction of sulfite to sulfide. In this study we use a large cluster model containing siroheme‐[4Fe4S] cofactor and protein residues involved in the direct interactions with the substrate, to get insight into the most feasible reaction mechanism and to understand the role of each considered active site component. In combination with earlier studies reported in the literature, our results lead to several interesting insights. One of the most important conclusions is that the reaction mechanism consists of three steps of two‐electron reduction of sulfur and the probable role of the siroheme‐[4Fe4S] cofactor is to ensure the delivery of packages of two electrons to the reactant.

中文翻译：

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异化亚硫酸还原酶催化的反应机理。 siroheme-[4FeS4] 辅因子的作用。

本工作是我们对异化硫酸盐还原途径研究的另一部分，涵盖了异化亚硫酸盐还原酶（dSIR）催化反应的理论研究。 dSIR 是参与该代谢途径的末端酶，它使用 siroheme-[4Fe4S] 辅因子将亚硫酸盐六电子还原为硫化物。在本研究中，我们使用包含西罗血红素-[4Fe4S]辅因子和参与与底物直接相互作用的蛋白质残基的大簇模型，以深入了解最可行的反应机制并了解每个考虑的活性位点组分的作用。结合文献中报道的早期研究，我们的结果得出了一些有趣的见解。最重要的结论之一是，反应机理由硫的双电子还原三个步骤组成，siroheme-[4Fe4S]辅助因子的可能作用是确保将两个电子包传递到反应物。