Conversion of rat xanthine dehydrogenase to xanthine oxidase during oxidative stress

The enzyme “xanthine oxidase” is one of the best characterized sources of superoxide anion and hydrogen peroxide. “in vivo” it mainly acts as a dehydrogenase which, by reducing NAD+, appears to be the physiologic form. Nevertheless under variety of conditions the enzyme can undergo a conversion to an oxidase which delivers the electrons to oxygen to form superoxide and hydrogen peroxide. The transformation xanthine dehydrogenase to xanthine oxidase is irreversible when it is induced by a proteolitic attack or reversible when the SH groups of the enzyme have been oxidized.