1. Discovery

2. Forms and nomenclature

3. Biosynthesis
     Chemical synthesis  

4. Metabolism

5. Participation in the urea cycle

6. Other biochemical roles
    Interactive pathway map  Neurotransmitter 

7. Applications & market
    Superabsorbent polymers  Additional uses 

8. Sources
    Dietary sources 

9. See also

10. References

11. External links

Aspartic acid (symbol Asp or D;^[4] the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins.^[5] Similar to all other amino acids it contains an amino group and a carboxylic acid. Its α-amino group is in the protonated –NH{{su|b=3|p=+}} form under physiological conditions, while its α-carboxylic acid group is deprotonated −COO⁻ under physiological conditions. Aspartic acid has an acidic side chain (CH₂COOH) which reacts with other amino acids, enzymes and proteins in the body.^[5] Under physiological conditions (pH 7.4) in proteins the side chain usually occurs as the negatively charged aspartate form, −COO⁻.^[5] It is a non-essential amino acid in humans, meaning the body can synthesize it as needed. It is encoded by all the codons GAU and GAC.

D-Aspartate is one of two D-amino acids commonly found in mammals.^[3]

In proteins aspartate sidechains are often hydrogen bonded to form asx turns or asx motifs, which frequently occur at the N-termini of alpha helices.

The L-isomer of Asp is one of the 22 proteinogenic amino acids, i.e., the building blocks of proteins. Aspartic acid, like glutamic acid, is classified as an acidic amino acid, with a pK_a of 3.9, however in a peptide this is highly dependent on the local environment, and could be as high as 14. Asp is pervasive in biosynthesis.

Discovery

Aspartic acid was first discovered in 1827 by Auguste-Arthur Plisson and Étienne Ossian Henry^[6] by hydrolysis of asparagine, which had been isolated from asparagus juice in 1806.^[7] Their original method used lead hydroxide, but various other acids or bases are more commonly used instead.

Forms and nomenclature

There are two forms or enantiomers of aspartic acid. The name "aspartic acid" can refer to either enantiomer or a mixture of two.^[8] Of these two forms, only one, "L-aspartic acid", is directly incorporated into proteins. The biological roles of its counterpart, "D-aspartic acid" are more limited. Where enzymatic synthesis will produce one or the other, most chemical syntheses will produce both forms, "DL-aspartic acid", known as a racemic mixture.

Biosynthesis

Because Aspartate can be synthesized by the body it is classified as a non-essential amino acid. In the human body, aspartate is most frequently synthesized through the transamination of oxaloacetate. The biosynthesis of aspartate is facilitated by an aminotransferase enzyme: the transfer of an amine group from another molecule such as alanine or glutamine yields aspartate and an alpha-keto acid.^[5]

Aspartate also plays an important role in the urea cycle.

Chemical synthesis

Racemic aspartic acid can be synthesized from diethyl sodium phthalimidomalonate,

(C₆H₄(CO)₂NC(CO₂Et)₂).^[9]

The major disadvantage of the above technique is that equimolar amounts of each enantiomer are made. Using biotechnology it is now possible to use immobilised enzymes to create just one type of enantiomer owing to their stereospecificity.

Metabolism

In plants and microorganisms, aspartate is the precursor to several amino acids, including four that are essential for humans: methionine, threonine, isoleucine, and lysine. The conversion of aspartate to these other amino acids begins with reduction of aspartate to its "semialdehyde", O₂CCH(NH₂)CH₂CHO.^[10] Asparagine is derived from aspartate via transamidation:

-O₂CCH(NH₂)CH₂CO₂- + GC(O)NH₃+ O₂CCH(NH₂)CH₂CONH₃+ + GC(O)O

(where GC(O)NH₂ and GC(O)OH are glutamine and glutamic acid, respectively)

Participation in the urea cycle

In the urea cycle, aspartate and ammonia donate amino groups leading to the formation of urea.

Other biochemical roles

Aspartate has many other biochemical roles. It is a metabolite in the urea cycle and participates in gluconeogenesis. It carries reducing equivalents in the malate-aspartate shuttle, which utilizes the ready interconversion of aspartate and oxaloacetate, which is the oxidized (dehydrogenated) derivative of malic acid. Aspartate donates one nitrogen atom in the biosynthesis of inosine, the precursor to the purine bases. In addition, aspartic acid acts as a hydrogen acceptor in a chain of ATP synthase.

Interactive pathway map

Neurotransmitter

Aspartate (the conjugate base of aspartic acid) stimulates NMDA receptors, though not as strongly as the amino acid neurotransmitter L-glutamate does.^[11]

Applications & market

As of 2014, the global market for aspartic acid is $117MM annually (50-60K MT/Yr)^[12] with potential areas of growth accounting for an {{clarify|text=addressable market|reason=Is this Total addressable market or Serviceable available market?|date=March 2017}} of $8.78BB.^[13] The three largest market segments include the U.S., Western Europe, and China. Current applications include biodegradable polymers (polyaspartic acid), low calorie sweeteners (aspartame), scale and corrosion inhibitors, and resins.

Nearly all aspartic acid is manufactured in China.

Superabsorbent polymers

One area of aspartic acid market growth is biodegradable superabsorbent polymers (SAP).{{synthesis inline|date=March 2017}} The superabsorbent polymers market is anticipated to grow at a CAGR{{clarify|date=March 2017}} of 5.5% from 2014 to 2019 to reach a value of $8.78BB globally.^[13] Around 75% of superabsorbent polymers are used in disposable diapers and an additional 20% is used for adult incontinence and feminine hygiene products. Polyaspartic acid, the polymerization product of aspartic acid, is a biodegradable substitute to polyacrylate.^[14] The polyaspartate market comprises a small fraction (est. < 1%) of the total SAP market.

Additional uses

In addition to SAP, aspartic acid has applications in the $19B fertilizer industry, where polyaspartate improves water retention and nitrogen uptake;^[15] the $1.1B (2020) concrete floor coatings market, where polyaspartic is a low VOC, low energy alternative to traditional epoxy resins;^[16] and lastly the >$5B scale and corrosion inhibitors market.^[17]

Sources

Dietary sources

Aspartic acid is not an essential amino acid, which means that it can be synthesized from central metabolic pathway intermediates in humans. However, aspartic acid is found in:

• Animal sources: oysters, luncheon meats, sausage meat, wild game
• Vegetable sources: sprouting seeds, oat flakes, avocado,^[18] asparagus,^[19] young sugarcane, and molasses from sugar beets.^[1]
• Dietary supplements, either as aspartic acid itself or salts (such as magnesium aspartate)
• The sweetener aspartame, an aspartic acid, phenylalanine, formaldehyde trimer (brands: NutraSweet, Equal, Canderel, etc.)

See also

• Aspartate transaminase
• Polyaspartic acid
• Sodium poly(aspartate), a synthetic polyamide

References

External links

• GMD MS Spectrum
• {{cite web |url=https://www.sciencedaily.com/releases/2010/04/100421121501.htm |title=Ancestral Eve' Crystal May Explain Origin of Life's Left-Handedness |author=American Chemical Society |date=21 April 2010 |website= |publisher=ScienceDaily |accessdate=2010-04-21| archiveurl= https://web.archive.org/web/20100423002752/https://www.sciencedaily.com/releases/2010/04/100421121501.htm| archivedate= 23 April 2010 | deadurl= no}}

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