Nitrites reaction with tryptophan

Satisfactory alternatives to the hydrolytic procedures have been sought for many years. Methods have been tried to produce colored derivatives by exploiting the reactivity of the indole nucleus in the intact protein (135, 353). Sodium hypochlorite, ferric chloride, cupric sulfate, bromine, and sodium nitrite, usually in acid solution, have been found to produce color with tryptophan-containing proteins. Later workers have formed other colored derivatives by reaction with tryptophan-specific reagents, while still others have used the characte-... 

Bonnett, R., and Holleyhead, R., 1974, Reaction of tryptophan derivatives with nitrite, J. Chem. Soc., Perkin I 962. 

Although the reaction of nitrous acid with peptides and proteins has been extensively used for analytical purposes (van Slyke estimation), the nature of the organic products has often been overlooked. Recently, Bonnett and Holleyhead 49) reported that treatment of N-acyl-tryptophan derivatives with sodium nitrite under mildly acidic conditions furnishes nitrosamines with the nitroso group located at the indolic nitrogen. 

The long known reaction of the indole nucleus of tryptophan with aldehydes under strongly acidic conditions to give colored products (135,287,397) was employed by Spies and Chambers (379) in a colorimetric procedure for the determination of tryptophan. In this method, the tryptophan-containing compounds (peptides or proteins) are dissolved in concentrated sulfuric acid containing / -dimethylamino-benzaldehyde (DAB) and a blue color is obtained after a prescribed time by adding sodium nitrite solution. 

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