64 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Those Hydrolysed. Those not Hydrolysed. 



Leucyl-1-tyrosine. Leucyl-leucine. 



Alanyl-glycyl-glycine. Aminobutyryl-glycine. 



Leucyl-glycyl-glycine. Aminobutyryl-aminobutyric acid A. 



Glycyl-leucyl-alanine. Aminobutyryl-aminobutyric acid B. 



Alanyl-leucyl-glycine. Valyl-glycine. 

 Dialanyl-cystine. Glycyl-phenylalanine. 

 Dileucyl-cystine. Diglycyl-glycine. 

 Tetraglycyl-glycine. Triglycyl-glycine. 

 Triglycyl-glycine ester (Curtius* biuret Dileucyl-glycyl-glycine. 



base). 



To which were added in 1907 and later years the following optically 

 active polypeptides : 



d-alanyl-d-alanine. d-alanyl-1-alanine. 



d-alanyl-1-leucine. 1-alanyl-d-alanine. 



d-alanyl-1-tyrosine. 1-leucyl-glycine. 



1-leucyl-l-leucine. 1-leucyl-d-leucine. 



I-leucyl-d-glutamic acid. d-leucyi-1-leucine. 



1-leucyl-l-tyrosine. 

 1-prolyl-l-phenylalanine. 

 d-alanyl-diglycyl-glycine. 



The hydrolysis of these compounds by the enzyme was determined 

 by the isolation of the individual substances. The isolation of the 

 amino acids soluble with difficulty in water, namely, tyrosine and cys- 

 tine, presented no great difficulty, since those compounds crystallised 

 out during the process of hydrolysis, but in the other cases the amino 

 acids required separation from unchanged dipeptide. The ester method 

 here again proved its usefulness ; the esters of the simple monoamino 

 acids are easily volatile in vacua and can be characterised by the 

 methods previously described ; those of the dipeptides are not volatile 

 and are characterised by conversion into their diketopiperazines or an- 

 hydrides by the action of ammonia, which compounds are less soluble 

 than the dipeptides themselves and are thus capable of separation by 

 filtration. 



By simply determining the change in rotation, especially when 

 optically active polypeptides were investigated, an indication that hy- 

 drolysis was occurring was obtained ; as soon as the rotatory power 

 became constant it was assumed that complete hydrolysis had taken 

 place and the solution was examined for the products of hydrolysis. 



In all cases the activity of the ferment was first proved, and freedom 

 from bacterial infection was specially guarded against and certified by 

 control experiments. 



* These are raccmic compounds. 



