Asparagine

Asparagine (abbreviated as Asn or N) is one of the 20 amino acids encoded in the genetic code. It has a carboxamide group as its side chain or functional group. In humans it is not an essential amino acid. The codons that code for it are AAU and AAC.

A reaction between asparagine and a reactive carbonyl or reducing sugar produces acrylamide (acrylic amide) in food when heated to a high enough temperature. These products are present in fried foods, such as straw potatoes, flakes, and roasted coffee.

History

Asparagine was isolated for the first time in 1805 by the French chemist Pierre Robiquet, who analyzed it in 1806 together with Louis-Nicolas Vauquelin, from asparagus juice, in which it is abundant, becoming the first amino acid to be isolated. The characteristic odor of the urine of individuals after consumption of asparagus is attributed to various metabolic byproducts of asparagine.

The name asparagine comes from the Greek (ἀσπάραγος) + -īn(a) quím. 'substance'.

Structural function in proteins

Because the asparagine side chain can form hydrogen bonds with the peptide backbone, asparagine residues are often found at the beginning and end of the alpha-helical structure, and in loops in beta sheets. Its role is believed to be to hog the hydrogen bonding interactions that would otherwise be satisfied by the polypeptide backbone. Glutamine, with an extra methylene group, has higher conformational entropy and is therefore less useful in this regard.

Asparagine also provides key sites for N-glycosylation, a modification of the protein chain with the addition of carbohydrate chains.

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Dietary sources

Asparagine is not an essential amino acid, which means that it can be synthesized from major metabolic pathway intermediates in humans and is not required in the diet. Asparagine is found in:

• Animal sources: dairy products and dairy serum, beef, poultry, eggs, fish and seafood.
• Vegetable sources: asparagus, potatoes, legumes (including soy), nuts and seeds.

Biosynthesis

The precursor of asparagine is oxaloacetate. Oxaloacetate is converted to aspartate by a transaminase enzyme. The enzyme transfers the amino group from glutamate to oxaloacetate, producing α-ketoglutaramate and aspartate. The enzyme asparagine synthetase produces asparagine, AMP, glutamate, and pyrophosphate from aspartate, glutamine, and ATP. In the asparagine synthetase reaction, ATP is used to activate aspartate, forming β-aspartyl-AMP. Glutamine donates an ammonium group, which reacts with β-aspartyl-AMP to form asparagine and three AMPs.

Degradation

Aspartate is a glucogenic amino acid. L-asparaginase hydrolyzes the amide group to form aspartate and ammonium. A transaminase converts aspartate to oxaloacetate, which can then be metabolized in the citric acid cycle or gluconeogenesis.

Deficit

Its deficiency can cause a series of disorders in the organism, among them alterations in the nervous system, metabolic alterations and alterations in brain functions.