Catalyzes the interconversion between carbon dioxide and water and the dissociated ions of carbonic acid (i.e. bicarbonate and hydrogen ions). H(+) + hydrogencarbonate = CO2 + H2O Inhibited by acetazolamide. Forms oligomers linked by disulfide bonds. Found on the surface microvilli and in the nucleus, particularly in nucleolus. Asn-325 bears high-mannose type glycan structures. Belongs to the alpha-carbonic anhydrase family.