44 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Those Hydrolysed. Those not Hydrolysed. 



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



* Alanyl-leucyl-glycine. Valyl-glycine. 

 Dialanyl-cystine. Glycyl-phenylalanine. 

 Dileucyl-cystine. Leucyl-proline. 

 Tetraglycyl-glycine. Diglycyl-glycine. 

 Triglycyl-glycine ester (Curtius' biuret Triglycyl-glycine. 



base). Dileucyl-glycyl-glycine. 



To which were added in 1907 the following optically active dipeptides : 



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



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



1-leucyl-l-leucine. 1-leucyl-glycine. 



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



d-leucyl-1-leucine. 



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 cystine, 

 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 vacuo and can be characterised by the methods pre- 

 viously described ; those of the dipeptides are not volatile and are 

 characterised by conversion into their diketopiperazines or anhydrides 

 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 

 hydrolysis 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. 



An examination of the results of hydrolysis by trypsin shows that 

 several factors have an important influence : 



i . The Structure of the Molecule. 



Glycyl-alanine, NH 2 . CH 2 . CO NH . CH(CH 3 ) . COOH, was not 

 hydrolysed, but the isomeric alanyl-glycine, NH 2 . CH(CH 3 ) . CO - 

 NH . CH 2 . COOH, was hydrolysed ; again, alanyl-leucine A was hydro- 

 lysed, but not leucyl-alanine. 



The order in which the amino acids are combined together in the 

 molecule has therefore a very marked effect. Thus, when alanine is 

 * These are racemic compounds. 



