Carbonic anhydrase

The carbonic anhydrases (or carbonate dehydratases) form a family of enzymes that catalyze the rapid interconversion of carbon dioxide and water to bicarbonate and protons (or vice versa), a reversible reaction that occurs relatively slowly in the absence of a catalyst. The active site of most carbonic anhydrases contains a zinc ion; they are therefore classified as metalloenzymes.

One of the functions of the enzyme in animals is to interconvert carbon dioxide and bicarbonate to maintain acid-base balance in blood and other tissues, and to help transport carbon dioxide out of tissues.

Reaction

The reaction catalyzed by carbonic anhydrase is:

The reaction rate of carbonic anhydrase is one of the fastest of all enzymes, and its rate is typically limited by the diffusion rate of its substrates. Typical catalytic rates of the different forms of this enzyme ranging between 10⁴ and 10⁶ reactions per second.

The reverse reaction is relatively slow (kinetics in the 15-second range) in the absence of a catalyst. This is why a carbonated drink does not instantly degas when opening the container; however it will rapidly degas in the mouth when it comes in contact with carbonic anhydrase that is contained in saliva.

Carbonic anhydrase 7

Carbonic anhydrase 7 (CA7) is an enzyme that in humans is encoded by the CA7 gene.

Function

Carbonic anhydrases are a large family of zinc metalloenzymes that catalyze the reversible hydration of carbon dioxide. They 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. They show extensive diversity in tissue distribution and in their subcellular localization. The cytosolic protein encoded by this gene is predominantly expressed in the salivary glands. Alternative splicing in the coding region results in multiple transcript variants encoding different isoforms.

References

Further reading

Carbonic anhydrase 9

Carbonic anhydrase 9 (CA9/CAIX) is an enzyme that in humans is encoded by the CA9 gene.

Carbonic anhydrases (CAs) are a large family of zinc metalloenzymes that catalyze the reversible hydration of carbon dioxide. They 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. They show extensive diversity in tissue distribution and in their subcellular localization. CAIX is a transmembrane protein and is a tumor-associated carbonic anhydrase isoenzyme. It is over-expressed in VHL mutated clear-cell renal cell carcinoma (ccRCC) and hypoxic solid tumors, but is low-expressed in normal kidney and most other normal tissues. It may be involved in cell proliferation and transformation. This gene is mapped to 9p13-p12.

CAIX has been licensed by the Dendreon Corporation. It is under development as a target for Autologous Cellular Immunotherapy. Product candidates targeted at CA9 are in preclinical development for the treatment of kidney, colon, and cervical cancer.