The Role of Molybdenum in Xanthine Oxidase and Related Enzymes: Reactivity with Cyanide, Arsenite, and Methanol

Abstract

The binding of arsenite, cyanide, or methanol by chicken liver xanthine dehydrogenase, milk xanthine oxidase, and rabbit liver aldehyde oxidase results in characteristic alterations in the absorption spectra of these enzymes. The coincidence between the kinetics of inhibition of all three enzymes and the rate of development of characteristic difference spectra has been established. These difference spectra have afforded a useful tool for investigating the binding sites of these inhibitors. The results indicate that all three ligands bind to the molybdenum component at the active center of each enzyme. Electron paramagnetic resonance spectra of native and arsenite- and cyanide-treated xanthine dehydrogenase have provided more definitive evidence for the binding of these inhibitors to enzymic molybdenum.