Uricase (EC:22.214.171.124) (urate oxidase) [PMID: 3182808] is the peroxisomal enzyme responsible
for the degradation of urate into allantoin:
Urate + O2 + H2O = 5-hydroxyisourate + H2O2
Some species, like primates and birds, have lost the gene for uricase and are therefore unable to degrade urate [PMID: 2594778]. Uricase is a protein of 300 to 400 amino acids, its sequence is well conserved.
It is mainly localised in the liver, where it forms a large electron-dense paracrystalline core in many peroxisomes [PMID: 2338140].
The enzyme exists as a tetramer of identical subunits,
each containing a possible type 2 copper-binding site [PMID: 2594778]. In legumes, 2 forms of uricase are found: in the roots, the tetrameric form; and, in the uninfected cells of root nodules, a monomeric form, which plays an
important role in nitrogen-fixation [PMID: 16593585].