Carbonic Anhydrase 3 (CA3) belongs to the Alpha-Carbonic Anhydrase family that encodes carbonic anhydrase isozymes. These carbonic anhydrases are a class of metalloenzymes that catalyze the reversible hydration of carbon dioxide and are differentially expressed in a number of cell types. The expression of the CA3 gene is strictly tissue specific and it is present at high levels in skeletal muscle with much lower levels found in cardiac and smooth muscle. CA3 is activated by proton donors such as imidazole and the dipeptide histidylhistidine. CA3 is inhibited by coumarins and sulfonamide derivatives such as acetazolamide.