Involved in the anaerobic nitrogen utilization via the assimilation of allantoin (PubMed:10601204, PubMed:20038185). 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 (PubMed:20038185). In vivo, the spontaneous release of S-ureidoglycolate and ammonia from S-ureidoglycine appears to be too slow to sustain an efficient flux of nitrogen (PubMed:20038185). allantoate + 2 H(+) + H2O = (S)-2-ureidoglycine + CO2 + NH4(+) Binds 2 Zn(2+) ions per subunit (PubMed:17362992). Also able to bind Mn(2+) (PubMed:25020232). Sulfate could be an allosteric effector of the enzyme that is responsible for stabilizing substrate binding. In addition, this anion effector may act as a counterion during enzyme-mediated catalysis. Optimum pH is 8. Less active under acidic conditions. Nitrogen metabolism; (S)-allantoin degradation. Homodimer. By glyoxylate and allantoin under anaerobic conditions. Belongs to the peptidase M20 family.