[Function of arginine in enzymes].

The average arginine content of proteins is 3.9%. Its frequency among the 20 amino acids of the proteins (13th position) is far lower than would be anticipated from the fact that 6 of the 61 codons for amino acids in the genetic code are arginine codons. Possible explanations for the relatively low frequency of arginine in proteins are discussed. The chemical and physicochemical properties of arginine, which are determined by the guanido group, and the method for chemical modification of arginine residues in proteins are described. The most important function of arginine residues in enzymes seems to be the recognition, binding, and orientation of anionic substrates and cofactors. This function is illustrated by numerous examples.