Carbonic anhydrases (CAs) are members of a large family of zinc metalloenzymes that catalyze the reversible hydration of carbon dioxide. CAs are involved in a variety of biological processes including respiration, calcification, acid-base balance and bone resorption, as well as the formation of aqueous humor, cerebrospinal fluid, saliva and gastric juice. They show extensive diversity in distribution and in their subcellular localization. Carbonic anhydrase II (gene name CA2), is one of sixteen forms of human α carbonic anhydrases. Carbonic anhydrase catalyzes reversible hydration of carbon dioxide. Defects in this enzyme are associated with osteopetrosis and renal tubular acidosis. Renal carbonic anhydrase allows the reabsorption of bicarbonate ions in the proximal tubule. Loss of carbonic anhydrase activity in bones impairs the ability of osteoclasts to promote bone resorption, leading to osteopetrosis.