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glutamine [key], organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer occurs in mammalian protein. Its structure is identical to that of glutamic acid, except that the acidic side-chain carboxyl group of glutamine has been coupled with ammonia, yielding an amide. The glutamic acid-glutamine interconversion is of central importance to the regulation of the levels of toxic ammonia in the body, and it is thus not surprising that when the concentrations of the amino acids of blood plasma are measured, glutamine is found to have the highest of all. Glutamine can donate the ammonia on its side chain to the formation of urea (for eventual excretion by the kidneys) and to purines (necessary for the synthesis of genetic material). Once glutamine is incorporated into proteins, its relatively unreactive side-chain amide participates in very few reactions. Glutamine is not essential to the human diet, since it can be synthesized in the body from glutamic acid. Glutamine was isolated from beet juice in 1883, but was not isolated from a protein until 1932; it was chemically synthesized in 1933.
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