Catalyzes the reversible hydration of carbon dioxide (PubMed:1909891, PubMed:1910042, PubMed:1336460, PubMed:8485129, PubMed:8399159, PubMed:8218160, PubMed:8262987, PubMed:8451242, PubMed:7901850, PubMed:7761440, PubMed:8639494, PubMed:9265618, PubMed:17330962, PubMed:9398308, PubMed:11327835, PubMed:12056894, PubMed:17346964, PubMed:12171926, PubMed:15453828, PubMed:16214338, PubMed:15865431, PubMed:16106378, PubMed:15300855, PubMed:15667203, PubMed:18942852, PubMed:11831900, PubMed:17251017). Can also hydrate cyanamide to urea (PubMed:10550681, PubMed:11015219). Stimulates the chloride-bicarbonate exchange activity of SLC26A6 (PubMed:15990874). Essential for bone resorption and osteoclast differentiation (PubMed:15300855). Involved in the regulation of fluid secretion into the anterior chamber of the eye. Contributes to intracellular pH regulation in the duodenal upper villous epithelium during proton-coupled peptide absorption. H(+) + hydrogencarbonate = CO2 + H2O urea = cyanamide + H2O Zinc. Can also use cobalt(II) with lower efficiency, but not copper(II), nickel(II) and manganese(II). Activated by X-ray, histamine, L-adrenaline, L- and D-phenylalanine, L- and D-histidine, L-His-OMe and beta-Ala-His (carnosine). Competitively inhibited by saccharin, thioxolone, coumarins, 667-coumate, celecoxib (Celebrex), valdecoxib (Bextra), SC-125, SC-560, diclofenac, acetate, azide, bromide, sulfonamide derivatives such as acetazolamide (AZA), methazolamide (MZA), ethoxzolamide (EZA), dichlorophenamide (DCP), brinzolamide, dansylamide, thiabendazole-5-sulfonamide, trifluoromethane sulfonamide and N-hydroxysulfamide, fructose-based sugar sulfamate RWJ-37497, and Foscarnet (phosphonoformate trisodium salt). Repressed strongly by hydrogen sulfide(HS) and weakly by nitrate (NO(3)). Esterase activity weakly reduced by cyanamide. N-hydroxyurea interfers with zinc binding and inhibit activity. Optimum pH is 6-8. Interacts with SLC4A4 (PubMed:14567693, PubMed:15218065). Interaction with SLC4A7 regulates SLC4A7 transporter activity (PubMed:14736710). Interacts with SLC26A6 isoform 4 (via C-terminus cytoplasmic domain) (PubMed:15990874). Colocalized with SLC26A6 at the surface of the cell membrane in order to form a bicarbonate transport metabolon. Displaced from the cytosolic surface of the cell membrane by PKC in phorbol myristate acetate (PMA)-induced cells. The disease is caused by variants affecting the gene represented in this entry. Target of drugs used in treatments against glaucoma disorder and breast cancer. Belongs to the alpha-carbonic anhydrase family.