18 THE AMINO ACIDS 



Proline was first isolated by Fischer from casein. Its pres- 

 ence in various other proteins was soon shown. 



Oxyproline. 



This amino acid was prepared from gelatin in 1902 by 

 Fischer. Its structure is not yet definitely established although 

 it undoubtedly possesses one of the following formulas. 



HO.CH - CH 2 CH2 - CH.OH 



II II 



CH 2 CH.COOH or CH 2 CH.COOH 



Tryptophane. /3-indole-a-amino-propionic acid. 

 C.CH 2 .CH.NH 2 .COOH 



NH' 



It was shown in 1826 by Tiedemann and Gmelin that when 

 chlorine or bromine water is added to a tryptic digestion 

 mixture a violet color is produced. Stadelmann named the 

 substance giving this reaction proteinochromogen and Neu- 

 meister proved that any severe treatment of protein would 

 cause the production of this compound to which he gave the 

 name tryptophane. Hopkins and Cole in 1902 isolated from 

 a tryptic digestion of casein a substance which gave all the 

 reactions of tryptophane, namely, the violet coloration with 

 bromine or chlorine, the Adamkiewicz reaction, and the pro- 

 duction of indole and skatole as a result of putrefaction. In 

 this manner the origin of the substances characteristic of 

 putrefaction was made clear. The structure of tryptophane 

 was regarded by Nencki as indole amino acetic acid. Ellinger, 

 however, showed it to be an indole amino propionic acid. 



Caseinic Acid, or diamino-trioxy-dodecanic acid. This 

 compound has been isolated by Skraup from casein only. Its 

 structure is still unknown. 



