Involved in the anaerobic nitrogen utilization via the assimilation of allantoin (PubMed:11344136). Catalyzes specifically the hydrolysis of allantoate to yield CO2, NH3 and S-ureidoglycine, which is unstable and readily undergoes a second deamination by S-ureidoglycine aminohydrolase AllE to yield S-ureidoglycolate and NH3 (By similarity). allantoate + 2 H(+) + H2O = (S)-2-ureidoglycine + CO2 + NH4(+) Binds 2 Zn(2+) ions per subunit. Nitrogen metabolism; (S)-allantoin degradation. Homodimer. Transcriptionally regulated by PucR. Expression is very low in excess nitrogen (glutamate plus ammonia) and is induced during limiting-nitrogen conditions (glutamate). Expression is further induced when allantoin is added during limiting-nitrogen conditions. Belongs to the peptidase M20 family.