Involved in the conversion of hydroxyisourate to ureides such as allantoin, the major form of nitrogen transport in legumes. 5-hydroxyisourate + H2O = 5-hydroxy-2-oxo-4-ureido-2,5-dihydro-1H-imidazole-5-carboxylate + H(+) Purine metabolism; urate degradation; (S)-allantoin from urate: step 2/3. Monomer. Highly expressed in uninfected root nodules. Detected in leaves, stems and roots. Expression in nodules increased with increasing plant age up to 21 days, then decreased. Belongs to the glycosyl hydrolase 1 family.