D-Aspartic acid

Aspartic acid (abbreviated as Asp or D; encoded by the codons [GAU and GAC]) is an ɑ-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated -+NH3 form under biological conditions), an α-carboxylic acid group (which is in the deprotonated –COO- form under biological conditions), and a side chain CH2COOH, classifying it as a charged(at physiological pH), aliphatic amino acid. It is semi-essential in humans, meaning the body can synthesize it from oxaloacetate.

Asp's L-isomer is one of the 23 proteinogenic amino acids, i.e., the building blocks of proteins. Asp (and glutamic acid) is classified as acidic, with a pKa of 3.9, however in a peptide this is highly dependent on the local environment (as with all amino acids), and could be as high as 14. Asp is pervasive in biosynthesis.