Aspartate

Aspartic acid (abbreviated as Asp or D) is an α-amino acid with the chemical formula HO2CCH(NH2)CH2CO2H. The L-isomer is one of the 20 proteinogenic amino acids, i.e. the building blocks of proteins. Its codons are GAU and GAC. It is classified as an acidic amino acid, together with glutamic acid. Aspartic acid is pervasive in biosynthesis. Like all amino acids, the location of acid protons depends on the pH of the solution and the crystallization conditions.

The abbreviation Asx (or B) represent either aspartic acid or asparagine.

Role in biosynthesis of amino acids
Aspartic acid is non-essential in mammals, being produced from oxaloacetate by transamination. In plants and microorganisms, aspartic acid is the precursor to several amino acids, including four that are essential: methionine, threonine, isoleucine, and lysine. The conversion of aspartic acid to these other amino acids begins with reduction of aspartic acid to its "semialdehyde," HO2CCH(NH2)CH2CHO. Asparagine is derived from aspartic acid via transamidation:
 * HO2CCH(NH2)CH2CO2H +  GC(O)NH2   HO2CCH(NH2)CH2CONH2  +  GC(O)OH

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

Other biochemical roles
Aspartic acid 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. Aspartic acid donates one nitrogen atom in the biosynthesis of inositol, the precursor to the purine bases.

Neurotransmitter
Aspartate (the conjugate base of aspartic acid) stimulates NMDA receptors, though not as strongly as the amino acid neurotransmitter glutamate does. It serves as an excitatory neurotransmitter in the brain and is an excitotoxin.

As a neurotransmitter, aspartic acid may provide resistance to fatigue and thus lead to endurance, although the evidence to support this idea is not strong.

Dietary Sources
Aspartic acid 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. Aspartic acid is found in:
 * Animal sources: luncheon meats, sausage meat, wild game,
 * Vegetarian sources: sprouting seeds, oat flakes, avocado, asparagus.

Chemical Synthesis
Racemic aspartic acid can be synthesized from diethyl sodium phthalimidomalonate, (C6H4(CO)2NC(CO2Et)2).