Responsible for the hydrolysis of cyanuric acid, an intermediate formed during catabolism of s-triazine based compounds in herbicides such as atrazine and polymers such as melamine. Catalyzes the hydrolytic opening of the s-triazine ring of cyanuric acid (2,4,6-trihydroxy-s-triazine) to yield carbon dioxide and carboxybiuret, which spontaneously decarboxylates to biuret. cyanurate + H2O = 1-carboxybiuret + H(+) Inhibited by barbituric acid. kcat is 2.2 sec(-1) with cyanuric acid as substrate. Xenobiotic degradation; atrazine degradation; biuret from cyanurate: step 1/1. Homotetramer. The monomer structure is formed from three repeating units (RUs) that share the same structure as one another. The monomer, the active site and substrate all possess threefold rotational symmetry, to the extent that the active site possesses three potential Ser-Lys catalytic dyads. It is possible that any or all of the three active-site serines may act as nucleophile (albeit only one can do so per catalytic cycle). Belongs to the cyclic amide hydrolase (CyAH) family.