AskDefine | Define asparagine

Dictionary Definition

asparagine n : a crystalline amino acid found in proteins and in many plants (e.g., asparagus)

User Contributed Dictionary

English

Alternative spellings

Noun

  1. A nonessential amino acid C4H8N2O3 found in plants such as asparagus.

Translations

nonessential amino acid C4H8N2O3
  • Spanish: asparagina

Extensive Definition

For other articles using the abbreviation or acronym asn see ASN.
Asparagine (abbreviated as Asn or N; Asx or B represent either asparagine or aspartic acid) is one of the 20 most common natural amino acids on Earth. It has carboxamide as the side chain's functional group. It is not an essential amino acid. Its codons are AAU and AAC.
A reaction between asparagine and reducing sugars or reactive carbonyls produces acrylamide (acrylic amide) in food when heated to sufficient temperature. These products occur in baked goods such as french fries, potato chips, and roasted coffee.

History

Asparagine was first isolated in 1806 from asparagus juice, in which it is abundant -- hence its name -- becoming the first amino acid to be isolated. The characteristic smell observed in the urine of individuals after their consumption of asparagus is attributed to various metabolic byproducts of asparagine.

Structural function in proteins

Since the asparagine side chain can form hydrogen bond interactions with the peptide backbone, asparagine residues are often found near the beginning and the end of alpha-helices, and in turn motifs in beta sheets. Its role can be thought as "capping" the hydrogen bond interactions which would otherwise be satisfied by the polypeptide backbone. Glutamines, with an extra methylene group, have more conformational entropy and thus are less useful in this regard.
Asparagine also provides key sites for N-linked glycosylation, modification of the protein chain with the addition of carbohydrate chains.

Sources

Dietary Sources

Asparagine is not an essential amino acid, which means that it can be synthesized from central metabolic pathway intermediates in humans and is not required in the diet. Asparagine is found in:
  • Animal sources: dairy, whey, beef, poultry, eggs, fish, lactalbumin, seafood
  • Vegetarian sources: asparagus, potatoes, legumes, nuts, seeds, soy, whole grains

Biosynthesis

The precursor to asparagine is oxaloacetate. Oxaloacetate is converted to aspartate using a transaminase enzyme. The enzyme transfers the amino group from glutamate to oxaloacetate producing α-ketoglutarate 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 free AMP.

Degradation

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

Function

The nervous system requires asparagine. It also plays an important role in the synthesis of ammonia.
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asparagine in Czech: Asparagin
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asparagine in Spanish: Asparagina
asparagine in Esperanto: Asparagino
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asparagine in Russian: Аспарагин
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asparagine in Ukrainian: Аспарагін
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asparagine in Slovak: Asparagín
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