Reversible hydration of carbon dioxide. H(+) + hydrogencarbonate = CO2 + H2O Inhibited by coumarins, saccharin, sulfonamide derivatives such as acetazolamide (AZA), benzenesulfonamide and derivatives (4-carboxyethylbenzene-sulfonamide, 4-carboxyethylbenzene-sulfonamide ethyl ester, 4-(acetyl-2-aminoethyl)benzene-sulfonamide, 4-aminoethylbenzene-sulfonamide) and Foscarnet (phosphonoformate trisodium salt). Homodimer. Highly expressed in colon, kidney, prostate, intestine and activated lymphocytes. Expressed at much higher levels in the renal cell cancers than in surrounding normal kidney tissue. Moderately expressed in pancreas, ovary and testis. Expressed in sweat glands and bronchiolar epithelium (PubMed:26911677). The disease is caused by variants affecting the gene represented in this entry. Belongs to the alpha-carbonic anhydrase family.