Nature of the catalytically labile oxygen at the active site of xanthine oxidase.
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.
Doonan
Christian J
CJ
Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada.
Stockert
Amy
A
Hille
Russ
R
George
Graham N
GN
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
D008982:Molybdenum; D014969:Xanthine Oxidase; D010100:Oxygen