Key enzyme in purine degradation. Catalyzes the oxidation of hypoxanthine to xanthine. Catalyzes the oxidation of xanthine to uric acid (By similarity). H2O + NAD(+) + xanthine = H(+) + NADH + urate H2O + hypoxanthine + NAD(+) = H(+) + NADH + xanthine Binds 1 Mo-molybdopterin (Mo-MPT) cofactor per subunit. Binds 2 [2Fe-2S] clusters per subunit. By 2-thiouric acid. Repressed by ammonium. Belongs to the xanthine dehydrogenase family.