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. kcat is 115 sec(-1) with barbituric acid as substrate. 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. PubMed:11748240 suggested that BAH was dependent upon Zn(2+), but according to PubMed:28235873, there is no indication of zinc in the structure: synchrotron X-ray fluorescence scans failed to detect a peak corresponding to zinc, and there was no indication of an atom with sufficient electron density in the resulting high-resolution structure. The enzyme does contain a metal cation, but the electron density identifies this cation as either Mg(2+) or Na(+) and not zinc.