Reversible hydration of carbon dioxide. H(+) + hydrogencarbonate = CO2 + H2O Inhibited by coumarins, sulfonamide derivatives such as acetazolamide (AZA), saccharin and Foscarnet (phosphonoformate trisodium salt). Strongest expression in heart, pancreas, kidney, placenta, lung, and skeletal muscle. Not expressed in liver. Belongs to the alpha-carbonic anhydrase family.