POLYPEPTIDES 75 



nature of the enzymes in yeast juice (endotryptase), in papain and in 

 the juice of nepenthes. The two former hydrolysed it and consequently 

 they contain tryptic enzymes ; the last had no action upon it, and the 

 enzyme of nepenthes is therefore like pepsin in its action. These re- 

 sults confirm the observations of other investigators, and the confusion 

 concerning the nature of these enzymes would appear to be now settled 

 with certainty. 



Glycyl-1-tyrosine serves only for distinguishing between a peptic 

 and a tryptic enzyme ; it is not possible to differentiate or compare 

 the activities of the tryptic enzymes, such as pancreatic trypsin, yeast 

 endotryptase, autolytic enzymes, etc., by its use even when the change 

 in rotation is observed as it is hydrolysed rapidly by all these enzymes 

 though the rates are slightly different. 



For this purpose the optically active dipeptides, d-alanyl-d-alanine 

 and d-alanyl-1-leucine were employed by Abderhalden and Koelker. 

 By observing the change in rotation they were able to determine the 

 rate at which these dipeptides were hydrolysed. They found that yeast 

 endotryptase was the most active, erepsin attacked the dipeptide more 

 slowly, and trypsin had scarcely hydrolysed them at all in forty-eight 

 hours. The differences were not sufficiently great to allow of a 

 differentiation. 



Optically active dipeptides were also of no value for the purpose of 

 distinguishing between the cells of normal organs, of organs in cases of 

 cancer, and of the actual tumours ; dl-leucyl-glycine, which was used as 

 substrate and compared with glycyl-1-tyrosine and 1-leucyl-diglycyl-gly- 

 cine, was in all cases hydrolysed most rapidly and in all cases 1-leucyl- 

 diglycyl-glycine was most slowly hydrolysed. The same products 

 were also formed ; the dl-leucyl-glycine was split asymmetrically with 

 the formation of d-leucyl-glycine, 1-leucine and glycine. 



In the cases of a tripeptide, tetrapeptide, etc., the point at which 

 the compound is first attacked may be different, and by choosing 

 a suitable substrate the change in rotation will show at which junction 

 hydrolysis first occurs. The first experiments in this direction were 

 made by Abderhalden and Koelker in 1 908. 



The specific rotation of 1-leucyl-glycyl-d-alanine is +20, that of 

 1-leucyl-glycine is +85, and that of glycyl-d-alanine is - 50. An in- 

 crease in rotation would show that d-alanine was first separated and 

 1-leucyl-glycine formed ; a decrease in rotation would point to a 

 separation of 1-leucine and the formation of glycyl-d-alanine according 

 to the following scheme : 



