Involved in the anaerobic nitrogen utilization via the assimilation of allantoin. 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. 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