The reactions of diazonium compounds with amino acids and proteins

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Abstract
Pauly (1915) has shown that the phenolic group of tyrosine and the imidazole group of histidine can react with diazo reagents. In a continuation of this work, reaction with other groups present in proteins was considered and derivatives were prepared with compounds containing certain amino groups and guanidino, sulfhydryl and indolyl groups. From the evidence of other authors it is also concluded that imino and aliphatic hydroxyl groups react, whereas all other groups are inert. Of the aliphatic primary amino compounds investigated, only those containing the grouping -CH2.NH2 yielded triazens. Other types of amino group were deaminated, an aromatic diazoamino compound being produced as the by-product. It is inferred that for amino acids found in proteins, only the epsilon-amino group of lysine and the alpha-amino group of glycine are capable of forming bis(diazo) amino links. The maximum amount of diazotized p-arsanilic acid which can react with four different proteins was determined and the values of the arsenic/nitrogen quotients were obtained by analysis. A comparison of these results with theoretical values calculated on the basis of their known amino acid content has given an indication of the extent of the reaction. It is concluded that reaction occurs between one diazonium radical and each sulfhydryl and indolyl group; between two diazonium radicals and each phenolic, imidazole, epsilon-amino group and alpha-amino group of N-terminal glycine residues; and between three diazonium radicals and each guanidino group. It is also concluded that alpha-amino groups of N-terminal residues other than glycine are deaminated.