Aspartic acid (abbreviated as Asp or D; Asx or B represent either aspartic acid or asparagine) is an α-amino acid with the chemical formula HOOCCH(NH2)CH2COOH. The carboxylate anion 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 4.0. 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.
Aspartic acid was first discovered in 1827 by Plisson, synthesized by boiling asparagine (discovered in 1806) with a base.
Forms and nomenclature
The term "aspartic acid" refers to either of two forms or a mixture of two. Of these two forms, only one, "L-aspartic acid", is directly incorporated into amino acids. 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. 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. Asparagine is derived from aspartate via transamidation:
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