Key enzyme involved in purine catabolism. Catalyzes the oxidation of hypoxanthine to xanthine and the oxidation of xanthine to urate. H2O + NAD(+) + xanthine = H(+) + NADH + urate H2O + hypoxanthine + NAD(+) = H(+) + NADH + xanthine Binds 2 [2Fe-2S] clusters. Binds 1 Mo-molybdopterin (Mo-MPT) cofactor per subunit. Homodimer. Belongs to the xanthine dehydrogenase family.