52 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



+ 20 



1-leucyl-glycyl-d-alanine 



It was observed 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. 



The tripeptide glycyl-d-alanyl-glycine was also investigated and the 

 point of first attack determined. The rotations of the various com- 

 pounds are : 



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< ^N 



glycyl-d-alanyl-glycine 



In the experiment 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. 



Further experiments were shortly afterwards made upon the com- 

 pounds, 



+ 30 + 22-4 



j- _ *- _ 



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



but here yeast endotryptase was also employed. By this enzyme 

 hydrolysis was effected in such a way that the rotation in both cases 

 gradually decreased which showed that d-alanine was first separated. 



The action of trypsin upon d-alanyl-glycyl-glycine was also deter- 

 mined. The hydrolysis took place differently ; the rotation decreased 

 a little, increased considerably and then again decreased. This shows 

 that glycine is first separated by trypsin, with the formation of d-alanyl- 

 glycine, whereas endotryptase first split off d-alanine. 



On account of this extraordinary difference the action of endotryptase 

 upon 1-leucyl-glycyl-alanine was examined. The rotation decreased and 

 became negative, which showed that this tripeptide was completely 



