Where is carbonic anhydrase in the body

This enzyme was first identified in , in red blood cells of cows. Since then, it has been found to be abundant in all mammalian tissues, plants, algae and bacteria.

This ancient enzyme has three distinct classes called alpha, beta and gamma carbonic anhydrase. Members of these different classes share very little sequence or structural similarity, yet they all perform the same function and require a zinc ion at the active site. Carbonic anhydrase from mammals belong to the alpha class, the plant enzymes belong to the beta class, while the enzyme from methane-producing bacteria that grow in hot springs forms the gamma class.

Thus it is apparent that these enzyme classes have evolved independently to create a similar enzyme active site. PDB entries 1ca2 , 1ddz and 1thj , shown here from top to bottom, are examples of the alpha, beta and gamma carbonic anhydrase enzymes, respectively. The zinc ions in the active site are colored blue in these figures.

Note that the alpha enzyme is a monomer, while the gamma enzyme is trimeric. Although the beta enzyme shown here is a dimer, there are four zinc ions bound to the structure indicating four possible enzyme active sites.

Other members of this class form tetramers, hexamers or octamers, suggesting that dimer is probably a building block for this class. Mammalian carbonic anhydrases occur in about 10 slightly different forms depending upon the tissue or cellular compartment they are located in. These isozymes have some sequence variations leading to specific differences in their activity.

Thus isozymes found in some muscle fibers have low enzyme activity compared to that secreted by salivary glands. While most carbonic anhydrase isozymes are soluble and secreted, some are bound to the membranes of specific epithelial cells.

For a deeper look at carbonic anhydrase from a genomic perspective, please visit the Protein of the Month feature at the European Bioinformatics Institute. Inhibitor green bound in the active site of carbonic anhydrase. Since this enzyme produces and uses protons and bicarbonate ions, carbonic anhydrase plays a key role in the regulation of pH and fluid balance in different parts of our body.

In our stomach lining it plays a role in secreting acid, while the same enzyme helps to make pancreatic juices alkaline and our saliva neutral. The transport of the protons and bicarbonate ions produced in our kidney and eyes influence the water content of the cells at these locations. Thus carbonic anhydrase isozymes perform different functions at their specific locations, and their absence or malfunction can lead to diseased states, ranging from the loss of acid production in the stomach to kidney failure.

When there is a build up of fluid that maintains the shape of our eyes, the fluid often presses on the optic nerve in the eye and may damage it. This condition is called glaucoma. In recent years, inhibitors of carbonic anhydrase are being used to treat glaucoma.

CO 2 produced within skeletal muscle has to leave the body finally via ventilation by the lung. To get there, CO 2 diffuses from the intracellular space into the convective transport medium blood with the two compartments, plasma and erythrocytes.

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