76 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



1-leucyl-glycyl-d-alanine 



+ 10 o + 2-4 



It was observed, with pancreatic extract and intestinal extract 

 together, that the rotation at first increased to an extent of about 40 

 per cent, and under these conditions 1-leucyl-glycine must be first formed 

 and alanine separated off. Later the rotation decreased, which was due 

 to the hydrolysis of 1-leucyl-glycine. Glycyl-d-alanine was apparently 

 not formed at all in the process of hydrolysis. With yeast extract the 

 rotation decreased, which showed that 1-leucine was first separated. 



The tripeptides glycyl-d-alanyl-glycine and d-alanyl-glycyl-glycine 

 were also investigated and the point of first attack determined. The 

 rotations of the various compounds are : 



- 64 + 3 



glycyl-d-alanyl-glycine and d-alanyl-glycyl-glycine 



- 50 + 50 + 50 



o + 2-4 o 2-4 o 



In the case of glycyl-d-alanyl-glycine, with both pancreatic extract 

 and yeast extract, the rotation decreased at first, was reversed in direc- 

 tion and then again decreased in amount Glycine and d-alanyl-glycine 

 must therefore have been formed first and the d-alanyl-glycine must 

 then have been subsequently hydrolysed. 



d-Alanyl-glycyl-glycine was hydrolysed by yeast extract, intestinal 

 extract and the juices of normal tissues in such a way that the rotation 

 gradually decreased showing that d-alanine was first separated. In the 

 case of a cancer tumour the reverse was observed : the initial rise in 

 rotation was followed by a fall which pointed to the separation of 

 glycine at the commencement of the attack. Trypsin had been 

 previously observed to effect the hydrolysis in the same way. 



The action of endotryptase and of pancreatic extract upon 1-leucyl- 

 glycyl-d-alanine was next examined. With the yeast extract the rota- 

 tion decreased and became negative, which showed that this tripeptide 

 was completely split open between the leucine and the glycine. With 

 trypsin 1-leucyl-glycine was first formed and d-alanine split off. 



The same differences were noted with the tetrapeptide, 



+ 22-4 



d-alanyl-glycyl-glycyl-glycine 



+ 30 ^"7"" 



