Carbonic Anhydrase IX (CA-IX) is an enzyme that is induced under hypoxic conditions. This enzyme is rarely present in normal cells and is responsible for controlling tumor pH. CA-IX is a transmembrane glycoprotein of the zinc metalloenzyme family. This family displays 15 isoforms in human tissues. Carbonic Anhydrase IX functions to convert carbonic acid present in hypoxic cells into a biocarbonate and a proton.