Hydrolyzes allophanate to NH(3) and CO(2). Can also use malonamate, but with much lower efficiency. 3 H(+) + H2O + urea-1-carboxylate = 2 CO2 + 2 NH4(+) Inhibited, in a time-dependent manner, by phenyl phosphorodiamidate, which forms a covalently modified Ser-189. kcat is 16.4 sec(-1) for allophanate. kcat is 0.1 sec(-1) for malonamate. Optimum pH is 9.5. Xenobiotic degradation; atrazine degradation. Homotetramer. Belongs to the amidase family.