Cyclic amide hydrolase of unknown substrate specificity. Catalyzes the hydrolytic ring-opening of a cyclic amide. Does not act on cyanuric acid nor barbituric acid. Homotetramer; disulfide-linked. The disulfide forms between 2 monomers in the tetramer, such that each tetramer contains 2 sets of vicinal disulfides. 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. The structural metal found in both cyanuric acid hydrolase and barbiturase is absent in the Frankia CyAH. Belongs to the cyclic amide hydrolase (CyAH) family.