Carbonic anhydrase is a family of metalloenzymes (enzymes that contain one or more metal atoms as a functional component of the enzyme) that catalyze the rapid interconversion of carbon dioxide and water into carbonic acid and protons. It also converts bicarbonate in carbon dioxide and water. This reaction occurs spontaneously in aqueous solution, but does so slowly. Carbonic anhydrase can greatly increase the rate of the reaction, with typical catalytic rates of the different forms of this enzyme ranging between 104 and 106 reactions per second. The active site of most carbonic anhydrases contains a zinc ion.