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(+) Amino-acid biosynthesis; beta-alanine biosynthesis. Homodimer, homotetramer, homooctamer; can also form higher homooligomers. Belongs to the carbon-nitrogen hydrolase superfamily. BUP family.