arginine, organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer participates in the biosynthesis of proteins. Its basic side chain adds a positive charge and hence a greater degree of water-solubility to proteins in neutral solution. Although arginine can be synthesized from cellular metabolites, it is usually considered essential to the diet of children for the maintenance of normal rates of growth. Arginine is the direct metabolic precursor of urea, the dominant nitrogenous waste product of most mammals. It was discovered in protein in 1895.

One of the essential amino acids, particularly abundant in histones and other proteins associated with nucleic acids. It plays an important metabolic role in the synthesis of urea, the principal form in which mammals excrete nitrogen compounds. Arginine is used in medicine and biochemical research, in pharmaceuticals, and as a dietary supplement.

Learn more about arginine with a free trial on Britannica.com.