HpxO is an FAD-dependent urate hydroxylase (EC 1.14.13.113). Like the factor independent urate hydroxylase (EC 1.7.3.3), it consumes O2 and converts urate to 5-hydroxyisourate, which decomposes spontaneously to allantoin and CO2. However, HpxO oxidizes NADH to NAD(+), and produces H20, while EC 1.7.3.3 produces H202 as a byproduct.
Jiyao W et al.(2023). "The conserved domain database in 2023.",