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 coumarins, saccharin, sulfonamide derivatives such as acetazolamide (AZA) and Foscarnet (phosphonoformate trisodium salt). Optimum pH is 6.5. Forms oligomers linked by disulfide bonds. Found on the surface microvilli and in the nucleus, particularly in nucleolus. Expressed primarily in carcinoma cells lines. Expression is restricted to very few normal tissues and the most abundant expression is found in the epithelial cells of gastric mucosa. By hypoxia. Asn-346 bears high-mannose type glycan structures. Belongs to the alpha-carbonic anhydrase family.