EXAFS studies of the molybdenum center of xanthine oxidase

EXAFS spectra associated with the K-absorption edge of molybdenum in the desulpho and functional forms of xanthine oxidase and some potential synthetic analogues have been obtained. These data indicate that the immediate environment of the molybdenum is different in the two forms of the enzyme and that desulpho xanthine oxidase resembles that in [MoO2(S2CNEt2)2] and [MoO2(ethylcysteine)2]. The cyanolysable sulphur atom of functional xanthine oxidase is suggested to be tightly bound to the molybdenum at a distance of less than or equal to 2.3 A.