glutamine

glutamine, 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.

One of the nonessential amino acids, closely related to glutamic acid. It is especially important in the cellular metabolism of animals as the only amino acid capable of readily crossing the blood-brain barrier. It is used in medicine and biochemical research and as a feed additive.

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Glutamine (abbreviated as Gln or Q; the abbreviation Glx or Z represents either glutamate or glutamic acid) is one of the 20 amino acids encoded by the standard genetic code. Its side chain is an amide formed by replacing the side-chain hydroxyl of glutamic acid with an amine functional group. It can therefore be considered the amide of the acidic amino acid glutamic acid. Its codons are CAA and CAG.

Nutrition

Occurrences in nature

Glutamine is the most abundant naturally occurring, non-essential amino acid in the human body and one of the only amino acids which directly crosses the blood-brain barrier. In the body it is found circulating in the blood as well as stored in the skeletal muscles. It becomes conditionally essential (requiring intake from food or supplements) in states of illness or injury.

Dietary sources

Dietary sources of L-glutamine include beef, chicken, fish, eggs, milk, dairy products, cabbage, beets, beans, spinach, and parsley. Small amounts of free L-glutamine are also found in vegetable juices and fermented foods, such as miso.

Functions

Glutamine has a variety of biochemical functions including:

1. A substrate for DNA synthesis
2. Major role in protein synthesis
3. Primary source of fuel for enterocytes (cells lining the inside of the small intestine).
4. Precursor for rapidly dividing immune cells, thus aiding in immune function
5. Regulation of acid-base balance in the kidney by producing ammonium
6. Alternative source of fuel for the brain and helps to block cortisol-induced protein catabolism
7. As a form of fixed nitogen by heterocysts, exchanged for photosynthate from undifferentiated cyanobacterial cells

Use

In catabolic states of injury and illness, GLN becomes conditionally-essential (requiring intake from food or supplements). Glutamine has been studied extensively over the past 10-15 years and has been shown to be useful in treatment of serious illnesses, injury, trauma, burns, cancer and its treatment related side-effects as well as in wound healing for postoperative patients. That is why it is now also classified as a nutraceutical. Glutamine is also marketed as a supplement used for muscle growth in weightlifting, bodybuilding, endurance and other sports.

Glutamine has also been taken to enhance brain function as it fuels two of the brain's most important neurotransmitters: glutamic acid and gamma-aminobutyric acid (GABA). It also assists in nitrogen transportation and reduces toxic build up of ammonia in the brain (though is contra-indicated for those with Reye's Syndrome). Hence, it has been used to aid memory, increase IQ in those with mental retardation, used to support those with schizophrenia and senility.

It has also been used in the treatment of ADHD, anxiety. and depression

It has also been used in recovery programs to break sugar craving cycles in alcoholics (although is contra-indicated for those with cirrhosis of the liver or kidney disease)and assist people in the management of sugar craving in diabetes.

It is also used as an anti-inflammatory in the treatment of autoimmune diseases and preserves Glutathione (important for detoxification and immune support) levels in the liver.

Glutamine is contraindicated for those with Reye's Disease, cirrhosis of the liver and kidney disease.

Aiding gastrointestinal function

In recent studies, glutamine-enriched diets have been linked with intestinal effects including maintenance of gut barrier function, intestinal cell proliferation, and differentiation. It may be used in recovery after gut surgery or in the treatment of gut damage, the treatment of sepsis, and irritable bowel syndrome. This may relate to the fact that the intestinal extraction rate of glutamine is higher than that for other amino acids, and is therefore thought to be the most viable option when attempting to alleviate conditions relating to the gastrointestinal tract.

These conditions were discovered after comparing plasma concentration within the gut between glutamine-enriched and non glutamine-enriched diets. However, even though glutamine is thought to have "cleansing" properties and effects, it is unknown to what extent glutamine has clinical benefits, due to the varied concentrations of glutamine in varieties of food.

Aiding recovery after surgery

It is also known that glutamine has various effects in reducing healing time after operations. Hospital-stay times after abdominal surgery can be reduced by providing parenteral nutrition regimes containing high amounts of glutamine to patients. Clinical trials have revealed that patients on supplementation regimes containing glutamine have improved nitrogen balances, generation of cysteinyl-leukotrienes from polymorphonuclear neutrophil granulocytes and improved lymphocyte recovery and intestinal permeability (in postoperative patients) - in comparison to those who had no glutamine within their dietary regime; all without any side-effects.

References

External links

• Nutrients and HIV: Part Three
• Supplemental uses