Глутамин: свойства, функции и источники

|Section6=
|Section7=

Glutamine (symbol Gln or Q) is an α amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge neutral, polar amino acid. It is non essential and conditionally essential in humans, meaning the body can usually synthesize sufficient amounts of it, but in some instances of stress, the body's demand for glutamine increases, and glutamine must be obtained from the diet. It is encoded by the codons CAA and CAG. It is named after glutamic acid, which in turn is named after its discovery in cereal proteins, gluten. In human blood, glutamine is the most abundant free amino acid. The dietary sources of glutamine include especially the protein rich foods like beef, chicken, fish, dairy products, eggs, vegetables like beans, beets, cabbage, spinach, carrots, parsley, vegetable juices and also in wheat, papaya, Brussels sprouts, celery, kale and fermented foods like miso. The one letter symbol Q for glutamine was assigned in alphabetical sequence to N for asparagine, being larger by merely one methylene –CH2– group. Note that P was used for proline, and O was avoided due to similarity with D. The mnemonic Qlutamine was also proposed. Regulation of acid base balance in the kidney by producing ammonium
Cellular energy, as a source, next to glucose
Nitrogen donation for many anabolic processes, including the synthesis of purines
Nontoxic transporter of ammonia in the blood circulation. Integrity of healthy intestinal mucosa, though small randomized trials have shown no benefit in Crohn's disease. Glutamine provides a source of carbon and nitrogen for use in other metabolic processes. Glutamine is present in serum at higher concentrations than other amino acids and is essential for many cellular functions. Examples include the synthesis of nucleotides and non essential amino acids. One of the most important functions of glutamine is its ability to be converted into α KG, which helps to maintain the flow of the tricarboxylic acid cycle, generating ATP via the electron carriers NADH and FADH2. The highest consumption of glutamine occurs in the cells of the intestines, and many cancer cells.

Glutamine is produced industrially using mutants of Brevibacterium flavum, which gives ca. 40 g/L in 2 days using glucose as a carbon source.

Glutamine synthesis from glutamate and ammonia is catalyzed by the enzyme glutamine synthetase. The majority of glutamine production occurs in muscle tissue, accounting for about 90% of all glutamine synthesized. Glutamine is also released, in small amounts, by the lungs and brain. Although the liver is capable of glutamine synthesis, its role in glutamine metabolism is more regulatory than productive, as the liver takes up glutamine derived from the gut via the hepatic portal system. In states where tissue is being built or repaired, like growth of babies, or healing from wounds or severe illness, glutamine becomes conditionally essential. The safety and efficacy of L glutamine oral powder were studied in a randomized trial of subjects ages five to 58 years old with sickle cell disease who had two or more painful crises within the 12 months prior to enrollment in the trial.

Glutamine is safe in adults and in preterm infants. Although glutamine is metabolized to glutamate and ammonia, both of which have neurological effects, their concentrations are not increased much, and no adverse neurological effects were detected. Adverse effects of glutamine have been described for people receiving home parenteral nutrition and those with liver function abnormalities. Although glutamine has no effect on the proliferation of tumor cells, it is still possible that glutamine supplementation may be detrimental in some cancer types. Ceasing glutamine supplementation in people adapted to very high consumption may initiate a withdrawal effect, raising the risk of health problems such as infections or impaired integrity of the intestine.]] Glutamine mouthwash may be useful to prevent oral mucositis in people undergoing chemotherapy but intravenous glutamine does not appear useful to prevent mucositis in the GI tract. Glutamine supplementation was thought to have potential to reduce complications in people who are critically ill or who have had abdominal surgery but this was based on poor quality clinical trials. Supplementation does not appear to be useful in adults or children with Crohn's disease or inflammatory bowel disease, but clinical studies as of 2016 were underpowered. Supplementation does not appear to have an effect in infants with significant problems of the stomach or intestines. Some athletes use L glutamine as supplement. Studies support the positive effects of the chronic oral administration of the supplement on the injury and inflammation induced by intense aerobic and exhaustive exercise, but the effects on muscle recovery from weight training are unclear.