 Its α-amino group is in the protonated –NH form under physiological conditions, while its α-carboxylic acid group is deprotonated −COO− under physiological conditions.Aspartic acid has an acidic side chain (CH2COOH) which reacts with other amino acids, enzymes and proteins in the body.Under physiological conditions (pH 7.4) in proteins the side chain usually occurs as the negatively charged aspartate form, −COO−.