The CA12 gene provides instructions for making a protein called carbonic anhydrase 12 (CA 12), which belongs to a family of proteins known as carbonic anhydrases. These proteins carry out a chemical reaction that involves the molecules carbon dioxide and water and produces a negatively charged bicarbonate molecule (bicarbonate ion) and a positively charged hydrogen atom (known as a proton). Carbonic anhydrases can also carry out the reverse reaction, forming carbon dioxide and water from bicarbonate. Carbon dioxide, bicarbonate, and protons are involved in many functions in the body; by regulating the levels of these substances, carbonic anhydrases play roles in several important processes. The presence of protons and bicarbonate affect the relative acidity (pH) of cells; one function of some carbonic anhydrases is to help maintain the correct cellular pH.

CA 12 is found in several tissues, including the sweat glands, kidneys, and large intestine. The protein likely helps regulate the transport of salt (sodium chloride or NaCl) in these tissues. Researchers suggest that channels that move salt in and out of cells are controlled in part by the pH of the cells. By regulating cellular pH, CA 12 may be able to control salt transport. In sweat glands, CA 12 is thought to play a role in determining how much salt is released from the body in sweat.