Involved in the degradation of cyanuric acid, an intermediate in the degradation of s-triazide herbicides such as atrazine (PubMed:21897878). Catalyzes the hydrolysis of biuret to urea-1-carboxylate (allophanate) and ammonia (PubMed:21897878, PubMed:29425231). The substrate, biuret, is formed by the spontaneous decarboxylation of carboxybiuret (PubMed:21897878). biuret + H2O = NH4(+) + urea-1-carboxylate Strongly inhibited by the sulfhydryl-modifying reagents N-ethylmaleimide and iodoacetamide (PubMed:21897878). Inhibited by the substrate analog N-carbamoyl aspartic acid (PubMed:29425231). kcat is 4.0 sec(-1) (PubMed:21897878). kcat is 11.9 sec(-1) (PubMed:29425231). Optimum pH is 8.5. Homotetramer. Belongs to the isochorismatase family.