A Density Functional Study of Active Site Models for Xanthine Oxidase

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• 作者：Mark R. Bray and Robert J. Deeth
• 刊名：Inorganic Chemistry
• 出版年：1996
• 出版时间：September 11, 1996
• 年：1996
• 卷：35
• 期：19
• 页码：5720 - 5724
• 全文大小：121K
• 年卷期：v.35,no.19(September 11, 1996)
• ISSN：1520-510X

文摘

The suggestion that hydroxide is coordinated to the oxidisedmolybdenum site in xanthine oxidase (XnO) istested theoretically by computing the structures of a range of four-,five-, and six-coordinate active site models.The local density approximation of density functional theory hasbeen used with the two experimentally verifiedsingly bonded sulfur ligands modeled by both dithiolene,[SRCCRS]^2- (R = H and CH₃), and thiolate,[CH₃S]^-groups. Both ligand types give virtually identical results foranalogous species. Based on a comparison of thecomputed M-L distances and those reported in recent EXAFS studies, itis concluded that both four- and six-coordination are unlikely since the optimized Mo-S contacts are tooshort or too long respectively. Of thefive-coordinate MoOS(SR)₂X models, the ones with X =[OH]^- give computed M-L bond lengths inexcellentagreement with the reported EXAFS data while X = H₂O,NH₃, [CH₃S]^-, andO^2- give relatively poor agreement.The theoretical results imply that the active site represents astable, preferred geometry rather than some imposedentatic state.