Catalyzes the hydroxylation of uric acid to 5-hydroxyisourate. H(+) + NADH + O2 + urate = 5-hydroxyisourate + H2O + NAD(+) Purine metabolism; urate degradation. Mutants show impaired utilization of both hypoxanthine and uric acid as nitrogen sources. Belongs to the FAD-dependent urate hydroxylase family.