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asparagine

Posted on 09. Jan, 2011 by .

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Asparagine is a nonessential amino acid, which means that it is manufactured from other amino acids in the liver; it does not have to be obtained directly through the diet.

Asparagine, also known as asparamide, is α-amino acid that is found in many proteins, particularly in plant proteins, such as in asparagus. Asparagine is closely related to the amino acid aspartic acid, into which it is easily hydrolized.

In humans, the L-isomer of asparagine, which is the only form that is involved in protein synthesis, is one of the 20 standard amino acids common in animal proteins and required for normal functioning in humans. However, asparagine is considered to be a “non-essential amino acid” since it does not have to be taken in with the diet, but can be synthesized by the human body from other compounds through chemical reactions—in this case, synthesized easily from aspartic acid.

The production of asparagine (utilizing various enzymes and chemical compounds), the incorporation of asparagine and other amino acids into proteins in a particular arrangement, and the folding of proteins into a precise three-dimensional configuration involves the coordination of a great number of complex steps, revealing the remarkable harmony in the universe.

Asparagine was first isolated in 1806 from asparagus juice, in which it is abundant—hence its name. Asparagine was the first amino acid to be isolated.

A reaction between asparagine and reducing sugars or reactive carbonyls produces acrylamide (acrylic amide) in food when heated to sufficient temperature, i.e. baking temperatures. Acrylamides are a chemical compound that some consider may pose health risks; they occur primarily in baked goods such as french fries, potato chips, and roasted coffee.

Asparagine is the amide of aspartic acid. The amide group does not carry a formal charge under any biologically relevant pH conditions. The amide is rather easily hydrolyzed, converting asparagine to aspartic acid. This process is thought to be one of the factors related to the molecular basis of aging.

Asparagine has a high propensity to hydrogen bond, since the amide group can accept two and donate two hydrogen bonds. It is found on the surface as well as buried within proteins.

Asparagine is a common site for attachment of carbohydrates in glycoproteins.

There is no suggested need for asparagine supplementation presently available in the literature. Asparagine is interrelated with the amino acid aspartic acid. Low levels of asparagine may indicate poor metabolism or synthesis of aspartic acid, which can result in the inability to properly synthesize and excrete urea, which is the major waste product of excess dietary protein. The inability to excrete urea can result in buildup of nitrogen-containing toxic metabolites that can lead to confusion, headaches, depression, irritability, or, in extreme cases, psychosis.

Deficiencies of a nonessential amino acid will not occur if a well-balanced diet is consumed because the intake of proper foods will allow the body to produce exactly the amount of amino acid required to function optimally.

Method of Action

Prior to 1940, amino acids were generally regarded as relatively-stable nutrient building blocks. In the 1940s and 50’s that concept was abandoned when it was found that the nitrogen atom in amino acids such as aspartic and glutamic acids 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 that 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 that 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.

Degradation

Asparagine can be degraded easily into aspartate (aspartic acid), which is a glucogenic amino acid. A glucogenic amino acid is an amino acid that can be converted into glucose through gluconeogenesis. Gluconeogenesis is the process of generating glucose from non-sugar carbon substrates like pyruvate, lactate, glycerol, and glucogenic amino acids.

Essentially, L-asparginase hydrolyzes the amide group of asparagine to form aspartate and ammonium. A transaminase converts the aspartate to oxaloacetate, which can then be metabolized in the citric acid cycle or via gluconeogenesis.

The characteristic smell observed in the urine of individuals after their consumption of asparagus is attributed to various metabolic byproducts of asparagine. In 1891, Marceli Nencki claimed that the substance responsible was methanethiol, and Robert White’s 1975 research indicated that the substances were various thioesters (Adams 1999). Other likely possibilities include asparagine aminosuccinic monoamide. Allison and McWhirter (1956) indicated that some individuals do not produce this odor after asparagus consumption, and that this is autosomal (on a non-sex chromosome); however, a re-examination in 1980 showed that these individuals are, rather, not able to detect the odor.

Uses

There is limited information concerning the use of asparagine inside the human body and more of its metabolic roles need to be studied. Concerning physical and mental health, there are indications that the presence or absence of sufficient asparagine may be of medical significance in some cases.

Asparagine is important for certain specific processes affecting the central nervous system and the amino acid may be of significant use in the maintenance, proper functioning, and overall chemical balance in the tissues making up the human brain. Extreme mood swings seem to be mediated by the presence of asparagine and the amino acid seems to assists the body in the maintenance of mental equilibrium. The presence of asparagine guards the mental from being either too overly anxious or nervous, or being too calm or sedated to the external environment.

Asparagine is also used in the body for physical processes. This amino acid is responsible for major amino acid transformations and all connected biochemical processes occurring inside the liver. The activation of metabolic pathways during the conversion of asparagine back to aspartic acid is probably this agency of biochemical importance. This process generates and releases metabolic energy for the maintenance of such important processes in the human body. Asparagine is additionally one of the major chemical precursor and facilitator involved in the synthesis of RNA, DNA, and the energy compound called ATP. The other biochemical processes that involve asparagine include the performance and functioning of anti-bodies, the bio-chemical conversion of aspartate to maintain cellular functioning and activity, the assembly of collagen and enzymatic activity, as well as cell to cell recognition in important cellular communication pathways.

Sources

Common dietary sources of asparagine include asparagus, dairy products, potatoes, beef, poultry, meat, and eggs

Usual dosage

The possible dosage or intake levels of any of the non-essential amino acids has not been clinically determined as deficiencies rarely occur in the body for this class of amino acids. The clinical estimates made by the U.S. National Academy of Sciences is stated with a recommendation that the majority of healthy people might achieve 0.36 grams of highly bio-available protein for every pound of bodyweight during supplementation – this equals 0.8 grams of protein, per kilogram of bodyweight per person.

thank you and references
http://www.biology.arizona.edu/biochemistry/problem_sets/aa/asparagine.html
http://www.springboard4health.com/notebook/proteins_asparagine.html
http://www.newworldencyclopedia.org/entry/Asparagine
http://www.herbs2000.com/amino_acids/asparagine.htm

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