Argininic acid is an α-amino acid that is used in the biosynthesis of proteins. In Vitro: Argininic acid (Arginine) contains an α-amino group, an α-carboxylic acid group, and a side chain consisting of a 3-carbon aliphatic straight chain ending in a guanidino group. In humans, arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health status of the individual.