Portal de Periódicos da CAPES

Diazotization of Proteins

1936; SAGE Publishing; Volume: 34; Issue: 1 Linguagem: Inglês

10.3181/00379727-34-8490c

1535-3702

Harry Eagle,

bioluminescence and chemiluminescence research

Proteins treated with nitrous acid are said to be “diazotized” insofar as, like true diazonium compounds, they couple in alkaline reaction with substances containing an aromatic OH or NH2 group, often forming a colored compound resembling the azo dyes. This reactivity of proteins is puzzling, since there is no known primary aromatic amine in protein which would react with HNO2 to form a diazonium compound. Flick contended that the reactivity of wool treated with HNO2 was due to the formation of a nitroso rather than a diazonium compound. More recently, Morel and Sisley, confirming previous work by Landsteiner with salicylic acid, have reported that tyrosine treated with nitrous acid forms a diazonium compound which couples with naphthol to form azo dyes. They therefore ascribed the reactivity of diazotized protein to its tyrosine content. Their contention remains plausible even if tyrosine forms a nitrosophenol instead of a diazonium compound on treatment with HNO2, as found in the case of phenol by Baeyer and Caro; for nitroso compounds might also couple with phenols and aromatic amines. The following data, however, indicate that tyrosine is not the only constituent of protein responsible for its diazotization. Instead, there is reason to believe that tryptophane is also responsible for the fact that protein treated with HNO2 couples with aromatic amines and hydroxyls. When tryptophane (or indole) was treated with nitrous acid in the cold, under the same conditions which lead to the “diazotization” of protein, a highly reactive compound was formed which gave a brilliant red color when added to α-naphthol in alkaline reaction (Table I). The HNO2, probably reacted with the indole NH to form a nitrosamine.