FAD-dependent urate hydroxylase (, HpxO enzyme, FAD-dependent urate oxidase, urate hydroxylase) is an enzyme with systematic name urate,NADH:oxygen oxidoreductase (5-hydroxyisourate forming). A non-homologous isofunctional enzyme (NISE) to HpxO was found, and named HpyO. HpyO was determined to be a typical Michaelian enzyme. These FAD-dependent urate hydroxylases are flavoproteins.
This enzyme catalyses the following chemical reaction