Involved in the catabolism of purine nucleotides. The sequential activity of AAH, UGLYAH and UAH allows a complete purine breakdown without the intermediate generation of urea. (S)-ureidoglycolate + 2 H(+) + H2O = CO2 + glyoxylate + 2 NH4(+) Binds 2 manganese ions per subunit. Nitrogen metabolism; (S)-allantoin degradation; glyoxylate from (S)-ureidoglycolate: step 1/1. Homodimer. Belongs to the peptidase M20 family.