Oxidizes hypoxanthine and xanthine to uric acid. PucA subunit could exert a molybdenum cofactor recruiting function. H2O + NAD(+) + xanthine = H(+) + NADH + urate H2O + hypoxanthine + NAD(+) = H(+) + NADH + xanthine Purine metabolism; hypoxanthine degradation; urate from hypoxanthine: step 1/2. Purine metabolism; hypoxanthine degradation; urate from hypoxanthine: step 2/2. Could be composed of four subunits: PucA, PucC, PucD and PucE. Expression is very low in excess nitrogen (glutamate plus ammonia) and is induced during limiting-nitrogen conditions (glutamate). Expression decreases when allantoin is added during limiting-nitrogen conditions.