Responsible for the hydrolysis of barbituric acid (2,4,6-trihydroxy-1,3-pyrimidine), an intermediate in the oxidative catabolism of pyrimidines. Catalyzes the hydrolytic opening of the pyrimidine ring of barbituric acid to yield ureidomalonic acid. barbiturate + H2O = 3-oxo-3-ureidopropanoate Inhibited by cyanuric acid. Pyrimidine metabolism; uracil degradation via oxidative pathway; malonate and urea from uracil: step 2/3. Homotetramer. The monomer structure is formed from three repeating units (RUs) that share the same structure as one another. The monomer and the active site possess nearly threefold rotational symmetry, to the extent that the active site possesses three potential Ser-Lys catalytic dyads, but one of the 3 active site surfaces varies in composition suggesting it is involved in confering substrate specificity. Belongs to the cyclic amide hydrolase (CyAH) family.