Characterization and Inhibition of the Recently Discovered Carbonic Anhydrase Isoforms CA XIII, XIV and XV

The carbonic anhydrase (CA) protein family consists of twelve active isozymes in humans and thirteen in most other mammals. The most recently discovered members of this family include cytosolic CA XIII and membrane-bound CAs XIV and XV. In this article we will review the characterization and inhibition profiles of these isozymes. CA XIII is expressed in the kidney as well as in the gastrointestinal and reproductive tracts, and therefore it may have a role in various physiological processes. The inhibition studies with CA XIII have shown that this isozyme can be inhibited efficiently with some sulfonamide inhibitors, while it is resistant to inhibition with chloride and bicarbonate ions. CA XIV is a membrane-bound enzyme that is expressed in numerous organs such as the brain, kidney, eye, liver and epididymis, where it has a role in the regulation of acid-base balance. The inhibitory properties of CA XIV have been studied, but no specific inhibitors have been found for this isozyme. The membrane-bound CA XV is an exceptional member of this protein family, because it is expressed in numerous species but absent in humans and chimpanzees. A detailed biochemical characterization of this isozyme is under way in our laboratories.