The Chemistry Book by Derek B Lowe

Author:Derek B Lowe
Language: eng
Format: epub
Publisher: Sterling

A Hubble Space Telescope image showing a portion of the Small Magellanic Cloud, a dwarf galaxy roughly 210,000 light-years from our own. Astronomers continue to use deuterium as a tracer for star and galaxy evolution.

1932

Carbonic Anhydrase

William C. Stadie (1886–1959), Francis John Worsley Roughton (1899–1972), Norman Urquhart Meldrum (1907–1933)

When carbon dioxide dissolves in water, it can also react to form carbonic acid, which, in turn, can revert into water and carbon dioxide. That’s not a particularly fast reaction in either direction—which is one reason that carbonated drinks don’t just suddenly blow off all their CO2 and go flat—but it becomes a speedy “diffusion controlled” reaction (with a rate that matches the time it takes for the individual molecules to get in and out of the enzyme’s active site) in the presence of carbonic anhydrase, one of the fastest enzymes known. British chemists Norman Urquhart Meldrum and Francis John Worsley Roughton and American chemists William C. Stadie and Helen O’Brien discovered the enzyme almost simultaneously in 1932, solving a longstanding mystery about how carbon dioxide behaves in the blood. How could it be circulated and then released so quickly for exhalation by the lungs?

The answer to this mystery was in the extreme speed and versatility of carbonic anhydrase, which is present in large amounts in red blood cells. If there’s a high concentration of carbon dioxide in the blood, the enzyme will produce bicarbonate, and if there’s a lot of bicarbonate, the enzyme will turn it back into carbon dioxide gas. In addition to exchanging the gas into the lungs, both reactions help cells regulate pH (among many other functions), and its role in respiration has led to inhibitor drugs for it being prescribed for altitude sickness.

But carbonic anhydrase is well liked by chemical biologists and enzyme engineers for other reasons. It’s easily (and cheaply) available in pure form and very stable on storage. Its structure has been thoroughly mapped out by X-ray crystallography, and its mechanism of action is very well understood. A zinc atom in the active site plays a key role, which made carbonic anhydrase the first confirmed “metalloenzyme,” a very important class of proteins. A huge variety of inhibitor compounds are available, with many of their binding modes also determined by X-ray studies.

SEE ALSO Carbon Dioxide (1754), Amino Acids (1806), X-Ray Crystallography (1912), Sulfanilamide (1932), Protein Crystallography (1965), Enzyme Stereochemistry (1975), Engineered Enzymes (2010)

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