Purine nucleotides are eventually degraded to ammonia and carbon dioxide. This pathway begins in the peroxisome and follows the degradation a urate intermediate to glyoxylate. The last three steps take place in the endoplasmic reticulum. First, uricase converts urate into 5-hydroxyisourate. Steps two and three are catalyzed by the bifunctional enzyme S-allantoin synthase: the conversion of 5-hydroxyisourate into 5-hydroxy-2-oxo-4-ureido-2,5-dihydro-1H-imidazole-5-carboxylate (OHCU) and the conversion of OHCU into S-allantoin. Fourth, allantoinase requires zinc ion as a cofactor to catalyze the conversion of S-allantoin into allantoate. Next allantoate must be transported out of the peroxisome and into the endoplasmic reticulum. Fifth, allantoate amidohydrolase catalyzes the conversion of allantoate into S-ureidoglycine. This enzyme is a homodimer and requires manganese ion as a cofactor. Sixth, ureidoglycine aminohydrolase requires a manganese ion as a cofactor to catalyze the conversion of S-ureidoglycine into S-ureidoglycolate. Seventh, ureidoglycolate amidohydrolase catalyzes the conversion of S-ureidoglycolate into glyoxylate.

Urate Degradation to Glyoxylate References