Reversible hydration of carbon dioxide. H(+) + hydrogencarbonate = CO2 + H2O Activated by histamine, L-adrenaline, L- and D-histidine, and L- and D-phenylalanine. Inhibited by coumarins, sulfonamide derivatives such as acetazolamide (AZA), by saccharin and Foscarnet (phosphonoformate trisodium salt). Belongs to the alpha-carbonic anhydrase family.