THE NITROUS 



ACID-NAPHTHYLETHYLENEDIAMINE 



REACTION FOR THE HISTOCHEMICAL 



DEMONSTRATION OF INDOLES 



L. E. THOMAS 



Biochemistry Research Department Good Samaritan Hospital, Portiand, 



Oregon (U. S. A.) 



When the histochemical procédure using nitrous acid and N-(l-naphthyl) 

 ethylenedi aminé for the démonstration of the tryptophan and other indoles 

 was introduced, it was proposed that the action of the nitrous acid led to 

 the formation of a N-nitroso compound. Meanwhile certain findings hâve 

 led to a différent proposai. The formation of a C-nitroso compound is propo- 

 sed. This reaction is discussed. It is proposed that further action of the 

 nitrous acid and an excess of hydrochloric acid reduces the nitroso com- 

 pound and couverts it to a diazonium compound. This is similar to the 

 reaction of tyrosine and certain other phénols with nitrous acid. 



The product of the action of nitrous acid on tryptophan (the diazonium 

 derivative) will couple with naphthylene derivatives other than N-(l-na- 

 phthyl) ethylenediamine under suitable conditions and the diazonium deri- 

 vative formed from tyrosine will couple with N-(l-naphthyl) ethylenediamine 

 in acid solution, Tyrosine does not, however, interfère with the original 

 tryptophan procédure because it forms a diazonium derivative much slower 

 than does tryptophan. The diazonium compound formed from tyrosine and 

 that formed from tryptophan are light-sensitive, the former being more 

 sensitive than the latter. Previous treatment of tryptophan with excess 

 formaldehyde blocks the reaction. The product of the reaction of thèse two 

 compounds has been reported to be a derivative of 3-carboline. 



The chemistry of the varions reactions and their significance in the 

 histochemical démonstration of indoles is discussed. 



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