xanthine dehydrogenase

Acts on a variety of purines and aldehydes, including hypoxanthine. The mammalian enzyme can also convert all-trans retinol to all-trans-retinoate, while the substrate is bound to a retinoid-binding protein. The enzyme from eukaryotes contains [2Fe-2S], FAD and a molybdenum centre. The mammalian enzyme predominantly exists as the NAD-dependent dehydrogenase (EC 1.17.1.4). During purification the enzyme is largely converted to an O2-dependent form, xanthine oxidase (EC 1.17.3.2). The conversion can be triggered by several mechanisms, including the oxidation of cysteine thiols to form disulfide bonds [which can be catalysed by EC 1.8.4.7, enzyme-thiol transhydrogenase (glutathione-disulfide) in the presence of glutathione disulfide] or limited proteolysis, which results in irreversible conversion. The conversion can also occur in vivo. Reaction: xanthine + NAD+ + H2O = urate + NADH + H+