Catalyzes the degradation of allantoate to (-)-ureidoglycolate and (+)-ureidoglycolate to glyoxylate. allantoate + H2O = (S)-ureidoglycolate + urea Vmax of the reaction with allantoate as substrate is nine times higher than that with ureidoglycolate. Optimum pH is 6.5 with allantoate as substrate, and 8 with ureidoglycolate as substrate. Optimum temperature is 60 degrees Celsius. Nitrogen metabolism; (S)-allantoin degradation; (S)-ureidoglycolate from allantoate (aminidohydrolase route): step 1/1. Homohexamer. Expressed in zygote. Expressed in the mating reaction and during early zygote formation. Belongs to the allantoicase family.