Reversible hydration of carbon dioxide. Carbon dioxide formed in the bicarbonate-dependent decomposition of cyanate by cyanase (CynS) diffuses out of the cell faster than it would be hydrated to bicarbonate, so the apparent function of this enzyme is to catalyze the hydration of carbon dioxide and thus prevent depletion of cellular bicarbonate (By similarity). H(+) + hydrogencarbonate = CO2 + H2O Binds 1 zinc ion per subunit. Oligomer. Belongs to the beta-class carbonic anhydrase family.