56 MICROSCOPIC TECHNIQUES 



PROTEIN REACTIONS 



Many of the tests for proteins are poorly adapted to histochemical 

 work because the strong acid or alkaU that they require has too 

 great a disintegrative eifect on the cellular structure. Tests which 

 particularly fall into this group are the biuret reaction for com- 

 ponent peptides, the xanthoproteic reaction for phenolic constitu- 

 ents, Millon's tyrosine reaction, Romieu's tryptophane test, the 

 tryptophane reaction of Voisenet-Flirth, and the diazo reaction for 

 histidine and tyrosine. Serra's arginine test, which is much less 

 drastic, and Berg's ninhydrin reaction for a-amino acid groups, 

 which uses no corrosive reagents although heating is required, will 

 both be described as well as two of the previous group, Millon and 

 Romieu reactions. 



ARGININE AND ARGININE-CONTAINING PROTEINS 



In another of those coincidences that occasionally turn up, Serra 

 at the University of Coimbra, Portugal, and Thomas at the Univer- 

 sity of Missouri, independently, and without knowledge of the other's 

 work, adapted the Sakaguchi (1925) reaction for arginine to its 

 histochemical identification. The reaction is based on the develop- 

 ment of an orange-red color with arginine when a-naphthol and 

 hypobromite or hypochlorite react with it in an alkaline medium. 



The first description of the method by Serra (1944a,b) was fol- 

 lowed by a report of Serra and Queiroz Lopes ( 1944) , who empha- 

 sized the usefulness of the reaction for the visualization of the basic 

 proteins such as those contained in cell nuclei. Subsequently, Serra 

 (1946) summarized the work of his group on the arginine reaction 

 in the course of a more general article dealing with histochemical 

 tests for proteins and amino acids. Serra pointed out that a positive 

 reaction is found only with arginine and the rather rare compounds 

 glycocyamine, gelegine, and agmatine, negative reactions being given 

 by guanidine, urea, ornithine, creatine, creatinine, asparagine, histi- 

 dine, and other amino acids. The reaction is specific for guanidine 

 derivatives in which one hydrogen atom of one or both amino groups 

 is substituted by an alkyl, fatty acid, or cyano radical. Substitution 

 of other radicals has not been tested, while guanidine derivatives in 

 which both hydrogen atoms of one amino group are substituted do 

 not give the color (Thomas, 1946) . 



