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Aspartate

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Aspartate

Aspartic acid
Identifiers
CAS number 617-45-8 YesY
56-84-8 (L-isomer)
1783-96-6 (D-isomer)
PubChem 424
ChemSpider 411 YesY
UNII 28XF4669EP YesY
EC-number 200-291-6
KEGG C16433 YesY
ChEBI CHEBI:22660 YesY
Jmol-3D images Image 2
Properties
Molecular formula C4H7NO4
Molar mass 133.10 g mol−1
Appearance colourless crystals
Density 1.7 g/cm3
Melting point

270°C

Boiling point

324°C (decomposes)

Solubility in water 4.5 g/L [2]
Acidity (pKa) 3.9
Hazards
MSDS External MSDS
EU Index not listed
NFPA 704
1
1
0
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Aspartic acid (abbreviated as D-AA, Asp, or D)[3] is an α-amino acid with the chemical formula HOOCCH(NH2)CH2COOH. The carboxylate anion, salt, or ester of aspartic acid is known as aspartate. The L-isomer of aspartate is one of the 20 proteinogenic amino acids, i.e., the building blocks of proteins. Its codons are GAU and GAC.

Aspartic acid is, together with glutamic acid, classified as an acidic amino acid with a pKa of 3.9, however in a peptide the pKa is highly dependent on the local environment. A pKa as high as 14 is not at all uncommon. Aspartate is pervasive in biosynthesis. As with all amino acids, the presence of acid protons depends on the residue's local chemical environment and the pH of the solution.

Discovery

Aspartic acid was first discovered in 1827 by Plisson, derived from asparagine, which had been isolated from asparagus juice in 1806, by boiling with a base.[4]

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.[3] 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.

Role in biosynthesis of amino acids

Aspartate is non-essential in mammals, being produced from oxaloacetate by transamination. It can also be generated from ornithine and citrulline in the urea cycle. 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.[5] 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)

Other biochemical roles

Aspartate is also 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 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 glutamate does.[6]

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. Aspartic acid is found in:

Chemical synthesis

Racemic aspartic acid can be synthesized from diethyl sodium phthalimidomalonate, (C6H4(CO)2NC(CO2Et)2).[7]

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. Aspartic acid is made synthetically using ammonium fumarate and aspartase from E.coli, E.coli usually breaks down the aspartic acid as a nitrogen source but using excess amounts of ammonium fumarate a reversal of the enzyme's job is possible, and so aspartic acid is made to very high yields, 98.7 mM from 1 M.

See also

References

External links

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