48 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Glycyl-1-tyrosine is readily hydrolysed by trypsin, but not by pepsin, 

 and it therefore serves an excellent compound for determining whether 

 a given proteolytic ferment behaves as a peptic or a tryptic enzyme. 

 For this reason it was employed by Abderhalden and Rona to deter- 

 mine the nature of the enzymes contained in the pyloric and duodenal 



