Catalyzes the reversible hydration of carbon dioxide to form bicarbonate. H(+) + hydrogencarbonate = CO2 + H2O Binds 1 zinc ion per subunit. Inhibited by sulfonamides and sulfamates. Active at pH 8.4 and inactive at pH 7.5. Homotetramer at pH 8.4 and homodimer at pH 7.4. Belongs to the beta-class carbonic anhydrase family.