Aspartic Acid

Aspartic acid (abbreviated as Asp or D) 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 -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 pK_a of 3.9, however in a peptide the pK_a is highly dependent on the local environment. A pK_a 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.