Catalyzes the oxidation of uric acid to 5-hydroxyisourate, which spontaneously decomposes to form allantoin. H2O + O2 + urate = 5-hydroxyisourate + H2O2 Inhibited by two structural analogs of urate, oxonate and xanthine. Optimum pH is 9.0. Purine metabolism; urate degradation; (S)-allantoin from urate: step 1/3. Heterotetramer. Belongs to the uricase family.