Key enzyme in purine degradation. Catalyzes the oxidation of hypoxanthine to xanthine. Catalyzes the oxidation of xanthine to uric acid. Contributes to the generation of reactive oxygen species. H2O + NAD(+) + xanthine = H(+) + NADH + urate H2O + hypoxanthine + NAD(+) = H(+) + NADH + xanthine H2O + O2 + xanthine = H2O2 + urate Binds 1 Mo-molybdopterin (Mo-MPT) cofactor per subunit. Binds 2 [2Fe-2S] clusters per subunit. Can be converted from the dehydrogenase form (D) to the oxidase form (O) irreversibly by proteolysis or reversibly through the oxidation of sulfhydryl groups. Homodimer. Interacts with BTN1A1. By interferon. Subject to partial proteolysis; this alters the enzyme from the dehydrogenase form (D) to the oxidase form (O). Contains sulfhydryl groups that are easily oxidized (in vitro); this alters the enzyme from the dehydrogenase form (D) to the oxidase form (O). Belongs to the xanthine dehydrogenase family.