General Features
Abbreviated: Asp or D
Molecular Formula: C4H7NO4
pKa: 2.10 (caboxyl), 9.82 (amino), 3.86(side chain)
Physiological Roles
Aspartate, also called aspartic acid, is an α-amino acid. Its codons are GAU and GAC. It is among the twenty amino acids that is proteinigenic, a building block for proteins. As told in the name it has acidic properties due to its side chain. There are two forms of aspartic acid, L-aspartic acid being the far more common and the form that is proteinigenic. It is a nonessential amino acid meaning that humans have pathways of synthesis for it.
Aspartic acid helps in the formation purines and pyrimidines which are key in DNA synthesis. In eukaryotes it is also plays an important role in the urea cycle in the form of argininosuccinic acid. One of the more interesting roles of aspartic acid in the human body is its role as a neurotransmittor. D-Aspartic acid has been found in the central nervous system of both vertebrates (rats) and invertebrates (mollusks) (D’Abuello et.al). High concentrations of D-Aspartate were found in synaptic vesicles of axon terminals. When nerve endings with high D-aspartate are stimulated, signal transduction is triggered by increasing the levels of the secondary messenger cAMP.
In bacteria aspartate plays an important role in chemotaxis. The chemotactic responses of bacteria such as Escherichia coli and Salmonella typhimurium are mediated by phosphorylation of the CheY protein. In the CheY protein there are two highly conserved residue of aspartate, Asp57, Asp13 (Lukat et al). The actual site of CheY phosphorilation is Asp57.
Aspartate biosynthesis is fairly straightforward. Oxaloacetate is converted to aspartate using a transaminase. The reaction can be revered so that aspartate can be converted back to oxaloacetate using an aspartate aminotransterase and ultimately end up in the citric acid cycle.
AST catalyzes the reversible transfer of an α-amino group between aspartate and glutamate and, as such, is an important enzyme in amino acid metabolism. AST is found in the liver, heart, skeletal muscle, aspartate transaminase
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