Catalyzes a late step in pyrimidine degradation. Converts N-carbamoyl-beta-alanine (3-ureidopropanoate) into beta-alanine, ammonia and carbon dioxide. Likewise, converts N-carbamoyl-beta-aminoisobutyrate (3-ureidoisobutyrate) into beta-aminoisobutyrate, ammonia and carbon dioxide. 3-(carbamoylamino)propanoate + 2 H(+) + H2O = beta-alanine + CO2 + NH4(+) 3-(carbamoylamino)-2-methylpropanoate + 2 H(+) + H2O = (R)-3-amino-2-methylpropanoate + CO2 + NH4(+) Allosteric enzyme with positive cooperativity toward the substrate N-carbamoyl-beta-alanine at low substrate concentrations (below 12 nM). Displays no cooperativity at substrate levels above 12 nM. Amino-acid biosynthesis; beta-alanine biosynthesis. Homodimer, homotetramer, homooctamer; can also form higher homooligomers. Detected in liver (at protein level). The N-terminus is blocked. Belongs to the carbon-nitrogen hydrolase superfamily. BUP family. The purified enzyme was shown to contain 1.8 zinc atoms per subunit, and sequence analysis was used to predict the zinc binding site (PubMed:8449931). The crystal structure of the human ortholog indicates a lack of bound zinc ions, and shows that the residues that were predicted to bind zinc are too far apart in space to form a zinc binding site (By similarity).