aspartic acid, organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer participates in the biosynthesis of proteins. Its acidic side chain adds a negative charge and hence a greater degree of water-solubility to proteins in neutral solution and has been shown to be near the active sites of some enzymes (see pepsin). Aspartic acid is not essential to the human diet. It was discovered in protein in 1868.

One of the nonessential amino acids, found in many proteins and closely related to asparagine. It is used in medical and biochemical research, as an organic intermediate, and in various industrial applications. It is one of the two components of aspartame.

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