134 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Tryptophane. 



The isolation of tryptophane by Hopkins and Cole in 1902 from 

 the mixture of products formed in the tryptic digestion of caseinogen 

 by precipitation in sulphuric acid solution with mercuric sulphate, 

 besides adding to our list of foundation-stones or units of the protein 

 molecule, gave us the explanation of three phenomena long known in 

 connection with the chemistry of the proteins; namely (i) of the reddish- 

 violet colour produced when chlorine or bromine water is added to a 

 tryptic digest ; (2) of the Adamkiewicz reaction ; (3) of the origin of 

 indole, skatole and related substances occurring in putrefaction. 



The first of these phenomena was described in 1826 by Tiedemann 

 and Gmelin. They observed that a reddish-violet colour was produced 

 on adding chlorine water to an extract of dog's pancreas. Cl. Bernard, 

 in 1856, showed that this reaction was given by a trypsin digest of 

 caseinogen, and Kiihne, in 1875, found that bromine water gave a better 

 reaction than chlorine water, whilst iodine did not produce the colour. 

 Kiihne showed also that this reaction was given by a pure trypsin 

 digest in presence of chloroform, i.e., without the intervention of micro- 

 organisms, and was, in fact, the first to point out the difference between 

 soluble ferments or enzymes, as he called them, and living ferments or 

 bacteria. Stadelmann called the then unknown substance proteino- 

 chromogen and the coloured body proteinochrome, whereas Neu- 

 meister, who showed that the reaction was obtained with any deep- 

 seated decomposition of protein, whether by trypsin, baryta water or 

 dilute sulphuric acid, gave the substance the name of tryptophane. This 

 name Hopkins and Cole gave to their crystalline substance as it gave 

 this reaction ; its presence in the digest causes the reaction. 



Shortly before Hopkins and Cole isolated tryptophane, they studied 

 the Adamkiewicz reaction the production of a violet colour when 

 concentrated sulphuric acid is added to a protein dissolved in glacial 

 acetic acid and found that it was caused by the presence of glyoxylic 

 acid in the glacial acetic acid, from which it arose by the action of sun- 

 light. On applying the glyoxylic reaction to tryptophane a very intense 

 colour was produced, and hence the presence of tryptophane in the 

 protein molecule is the cause of this reaction. 



According to Cole, the Liebermann reaction an intense blue colour 

 when proteins are precipitated by alcohol and washed with ether and 

 then heated with concentrated hydrochloric acid is also due to the 

 presence of tryptophane in the protein and to glyoxylic acid in the 



