74 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



tion. A control should be made of the optical changes occurring in 

 the enzyme solution under the same conditions. 



The change in rotation of the glycyl-1-tyrosine or silk peptone 

 solution may be observed as well as the separation of tyrosine. In 

 testing for enzymes in various bacteria Abderhalden, Pincussohn and 

 Walther used not only silk peptone, but peptones prepared in the 

 same way from edestin, gelatin and egg albumin as substrate, observing 

 the change in rotation as the means of detection. Though the results 

 were in general the same certain differences could be observed. 



Koelker has used racemic alanyl-glycine as substrate for testing the 

 activity of a yeast extract in an attempt to separate out the proteoclastic 

 enzyme 



Kober, who has found that alkali precipitates copper hydrate from 

 the copper salts of amino acids, suggests that this reaction might be 

 used for detecting proteoclastic enzymes, as dipeptides, etc., do not 

 form salts. The mixture of polypeptide and amino acid is boiled 

 with copper oxide and filtered : the blue solution, if amino acids be 

 present, is then treated with alkali and the copper oxide collected and 

 weighed. 



//. Differentiation of Enzymes. 



Glycyl-1-tyrosine is readily hydrolysed by trypsin but not by pep- 

 sin. It therefore serves as an excellent compound for determining 

 whether a given proteoclastic ferment behaves as a peptic or as a tryptic 

 enzyme. 



For this reason it was employed by Abderhalden and Rona to 

 ascertain the nature of the enzymes contained in the pyloric and 

 duodenal juices. Since neither of these juices acted upon glycyl-1- 

 tyrosine they must be regarded as peptic in their nature. 



Normally pancreatic juice never enters the stomach, but on a diet 

 rich in fat bile and pancreatic enzymes may pass back into this cavity. 

 The detection of trypsin under these conditions has been a matter of 

 difficulty, but Abderhalden and Medigreceanu have been able to 

 demonstrate its presence in the juice flowing from a pyloric fistula in a 

 dog, when it was fed with oil. The juice was immediately neutralised 

 and tested with glycyl-1-tyrosine. Tyrosine was split off. The pres- 

 ence of trypsin in the gastric contents in human subjects after a diet 

 containing plentiful fat can also be demonstrated in this way if the 

 contents are neutralised with magnesia (Abderhalden and Schitten- 

 helm). 



Abderhalden and Teruuchi used glycyl-1-tyrosine to determine the 



