Nature of the catalytically labile oxygen at the active site of xanthine oxidase
Date
2005
Authors
Doonan, C.
Stockert, A.
Hille, R.
George, G.
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Journal article
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Journal of the American Chemical Society, 2005; 127(12):4518-4522
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Christian J. Doonan, Amy Stockert, Russ Hille, and Graham N. George
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Abstract
In this paper we report the results of molybdenum K-edge X-ray absorption studies performed on the oxidized active site of xanthine oxidase at pH 6 and 10. These results indicate that the active site possesses one terminal oxygen ligand (Mo=O), two thiolate ligands (Mo-S), one terminal sulfido ligand (Mo=S), and one Mo-OH moiety. EXAFS analysis demonstrates that the Mo-OH bond shortens from 1.97 A at pH 6 to 1.75 A at pH 10, which is consistent with the generation of a Mo-O- moiety. This study provides convincing structural evidence that the catalytic oxygen donor at the oxidized active site of xanthine oxidase is Mo-OH rather than the Mo-OH2 ligation previously suggested by X-ray crystallography. These results support a mechanism initiated by base-assisted nucleophilic attack of the substrate by Mo-OH.
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Copyright © 2005 American Chemical Society