Catalyzes the catabolism of the allantoin degradation intermediate (S)-ureidoglycolate, generating urea and glyoxylate. Involved in the utilization of allantoin as nitrogen source (By similarity). (S)-ureidoglycolate = glyoxylate + urea Nitrogen metabolism; (S)-allantoin degradation. Homodimer. Belongs to the ureidoglycolate lyase family.