Carbonic anhydrase is a crucial enzyme that operates in animal cells, plant cells, and in the environment to stabilize carbon dioxide concentrations. Without this enzyme, the conversion from carbon dioxide to bicarbonate, and vice versa, would be extremely slow, and it would be nearly impossible to carry out life processes, such as photosynthesis in plants and people exhaling carbon dioxide during respiration. Although it performs a lot of beneficial functions, it can also damage the human body as well, even causing some forms of cancer.
Carbon dioxide is produced as waste from breaking down sugars and fats and in respiration, so it has to be transported through the body to the lungs. Carbonic anhydrase converts CO2 to carbonic acid as it's transported by blood cells, before being converted back to carbon dioxide. As many bodily functions are dependent on a certain pH, carbonic anhydrase adjusts the acidity of the chemical environment to prevent damage to the body.
Like animal cells, plant cells transport carbon dioxide gas as bicarbonate before converting it back to use it in photosynthesis to generate nutrition for the plant. One difference is that plant cells obtain carbon dioxide from air and soil instead of producing it. The structure can be almost completely different since it has a different amino acid sequence, and uses a zinc metal ion, which interacts with the oxygen atoms, also in a different mechanism from that of humans and animals. The plant version is found in the liquid part of the cell, while the animal version is found in cell mitochondria.
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In the Ocean
Atmospheric CO2 is taken up in the ocean by carbonic anhydrase and converted to carbonic acid, lowering the overall pH of the ocean over time. As more and more carbon dioxide is released and then removed from the atmosphere, the ocean becomes more acidic, having potential damaging effects for marine life. Marine algae then take up dissolved bicarbonate ions and convert them to carbon dioxide.
Stopping Carbonic Anhydrase
Although the enzyme is beneficial in many cases, it also catalyzes negative impacts on the body, and a special type of drug, called a carbonic anhydrase inhibitor, is available to counter this activity. A disease caused by this enzyme's activity, but not the enzyme itself, is glaucoma, in which pressure from acidic fluid buildup decreases eyesight over time. Some forms of cancer are also accelerated by carbonic anhydrase as well, including ovarian, breast, colon and kidney cancers.