Carbonic anhydrase
（重定向自Carbonate dehydratase）
![](/Images/godic/202501/03/Carbonic_anhydrase3952.png")
![Close-up rendering of active site of human carbonic anhydrase II, showing three histidine residues and a hydroxide group coordinating (dashed lines) the zinc ion at center. From PDB: 1CA2.](/Images/godic/202501/03/Carbonic_anhydrase_1CA2_active_site3952.png")
![Ribbon diagram of human carbonic anhydrase II. Active site zinc ion visible at center. From PDB: 1CA2.](/Images/godic/202501/03/Carbonic_anhydrase_1CA23952.png")
The carbonic anhydrases (or carbonate dehydratases) form a family of enzymes that catalyze the rapid interconversion of carbon dioxide and water to bicarbonate and protons (or vice versa), a reversible reaction that occurs relatively slowly in the absence of a catalyst. The active site of most carbonic anhydrases contains a zinc ion; they are therefore classified as metalloenzymes.