PROTEINS. 73 



It has recently been claimed that cystine occurs in two forms, 

 i. e. } stone-cystine and protein-cystine and that these two forms are 

 distinct in their properties. This view is incorrect. 



CYSTINE. 



For a discussion of cystine sediments in urine see Chapter XX. 



Tryptophane, C 11 H 12 N 2 O 2 , According to Ellinger, tryptophane 

 is indol-amino-propiomc add. Recently Ellinger and Flamand have 

 shown that it possesses the following formula: 



C-CH 2 .CH(NH 2 )-COOH 



NH 



Tryptophane is the mother-substance of indole, skatole, skatole 

 acetic acid and skatole carboxylic add, all of which are formed as 

 secondary decomposition products of proteins. Its presence in 

 protein substances may be shown by means of the Adamkiewicz 

 reaction or the Hopkins-Cole reaction (see page 91). It may be 

 detected in a tryptic digestion mixture through its property of giving 

 a violet color-reaction with bromine water. Tryptophane is yielded 

 by nearly all proteins but has been shown to be entirely absent from 

 zein, the prolamin (alcohol-soluble protein) of maize. 



Solutions of tryptophane in sodium hydroxide are dextro-rotatory. 

 Upon being heated to 266 C. tryptophane decomposes with the evo- 

 lution of gas. 



