Carbonic anhydrases (CAs) are a large family of zinc metalloenzymes that catalyze the reversible hydration of carbon dioxide. CAs participate in a variety of biological processes, including respiration, calcification, acid-base balance, bone resorption, and the formation of aqueous humor, cerebrospinal fluid, saliva, and gastric acid. CA12, also known as Car12 and carbonic anhydrase XII, is a type I membrane enzyme that is highly expressed in normal tissues, such as colon, kidney, prostate, intestine and activated lymphocytes and moderately expressed in pancreas, ovary, and testis. It has been found to be overexpressed in 10% of clear cell renal carcinomas.