title: Nature of the catalytically labile oxygen at the active site of xanthine oxidase.
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.
authors.affiliation: Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada.
authors.forename: Christian J
authors.initials: CJ
authors.lastname: Doonan
authors.forename: Amy
authors.initials: A
authors.lastname: Stockert
authors.forename: Russ
authors.initials: R
authors.lastname: Hille
authors.forename: Graham N
authors.initials: GN
authors.lastname: George
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D006863:Hydrogen-Ion Concentration; D008982:Molybdenum / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D013052:Spectrometry, X-Ray Emission / Q000379:methods; D014969:Xanthine Oxidase / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008982:Molybdenum; D014969:Xanthine Oxidase; D010100:Oxygen