Glutamine
Description
Glutamine is a nonessential amino acid, which means it is manufactured from other amino acids in the liver; it does not have to be obtained directly through the diet.
Glutamate (glutamic acid) is converted in the liver to glutamine through the addition of ammonia. Therefore, glutamine is important in ammonia detoxification. Glutamine is useful in the brain as a neurotransmitting substance.
Glutamine synthesis and degradation in the kidney help regulate the body's acid-base balance and electrolyte levels. Glutamine levels are higher in the blood than those of many other amino acids and are thought to play an important role in removing ammonia, which is the toxic metabolite from protein of tissues. The interconversion of glutamine and glutamate is dependent upon adequate levels of vitamin B-6.
Low levels of glutamine may be associated with increasing acidity and increased loss from the body of minerals such as calcium, magnesium, sodium, and potassium. Individuals with low levels of glutamine may be more susceptible to "Chinese Restaurant Syndrome" and need enhanced levels of vitamin B-6 to prevent this condition when they eat MSG-laden foods.
Glutamine has been used to treat individuals with certain types of brain biochemical problems, liver problems, and mineral deficiency signs from the loss of potassium, sodium, magnesium, and calcium. Dr. Roger Williams has suggested it may have value in managing alcoholism.
Recommended Dietary Allowances
An RDA has not been established for glutamine because it is a nonessential amino acid. Glutamine is considered a relatively safe amino acid and is consumed in the food daily at levels of several grams. Its therapeutic dose has been 100-1,000mg per day.
Food Sources
Glutamine is a nonessential amino acid, which means it is manufactured from other amino acids in the liver; it does not have to be obtained directly through the diet.
Method of Action
Prior to 1940, amino acids were generally regarded as relatively-stable nutrient building blocks. In the 1940s and '50s that concept was abandoned when it was found the nitrogen atom in amino acids, such as aspartic acid and glutamic acid, could be rapidly converted from one amino acid carbon skeleton to another.
The process by which these nitrogen atoms are exchanged is called transamination and is dependent upon the coenzyme pyridoxal pyrophosphate, which is derived from vitamin B-6. Both aspartic acid and glutamic acid can incorporate ammonia, thereby resulting in the production of asparagine and glutamine, respectively.
It soon became apparent asparagine and glutamine are soluble, nontoxic carriers of additional ammonia in the form of their amid groups. An active enzyme converts aspartate and ammonia to asparagine and glutamate and ammonia to glutamine. The nitrogen in glutamine is used in a great variety of biochemical processes, including the formation of carbamoyl phosphate used in the urea cycle and the production of purines, which are used in DNA and RNA.
Glutamate, glutamine, and aspartate also play central roles in the removal of all nitrogen from organic compounds. The exchange of nitrogen by transamination is reversible so when the body is properly managing glutamate and aspartate, there is the exchange of nitrogen from one source, ultimately, from the urea cycle and the elimination in the urine as urea.
References
Blackburn, G.L., Grant, J.P., Young, V.R., ed. Amino Acids Metabolism and Medical Applications.
Munro, H.N. & Crim, M.C. The Proteins and Amino Acids. Modern Nutrition in Health and Disease, eds. R.S. Goodhart & M.E. Shils, 6 ed., Philadelphia: Lea and Febiger, 1980.
Olney J., Labruyere, J., & DeGubareff T. Brain Damage in Mice from Voluntary Ingestion of Glutamate and Aspartate. Neurobehav. Toxicol., 2:125-9, 1980.
Windmueller & Spaeth. Metabolism of Absorbed Aspartate, Asparagine & Arginine by Rat Small Intestine In Vivo. Arch. Biochem. Biophys., 175:670-6, 1976.
Windmueller, H.G. & Spaeth, A.E. Intestinal Metabolism of Glutamine and Glutamate from the Lumen as Compared to Glutamine from Blood. Arch. Biochem. Biophys., 171:662-72, 1975.
Young, V.R., Meguid, M., Meredith, D.E., & Bier, D.M. Recent Developments in Knowledge of Human Amino Acid Requirements. Nitrogen Metabolism in Man, eds: J.C. Waterlow & J.M.L. Stephen, London: Applied Science Publishers, 1981.
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