Involved in the catabolism of purine nucleotides. Can use (S)-ureidoglycolate as substrate, but not (R)-ureidoglycolate or allantoate. 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. Can also use nickel and cobalt with lower activity. kcat is 1.43 sec(-1) with (S)-ureidoglycolate as substrate (at pH 8.5 and 30 degrees Celsius) (PubMed:25020232). kcat is 7.9 sec(-1) for (S)-ureidoglycolate (PubMed:19935661). Nitrogen metabolism; (S)-allantoin degradation; glyoxylate from (S)-ureidoglycolate: step 1/1. Homodimer. No visible phenotype under normal growth conditions, but mutant plants show a slight reduction of growth on a medium containing allantoin as the sole nitrogen source and accumulate ureidoglycolate. Belongs to the peptidase M20 family. Truncated N-terminus.