66 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



the ester of triglycyl-glycine, or the biuret base of Curtius, which had 

 been previously examined by Schwarzschild. The length of the glycine 

 chain is therefore of importance, but an alteration in the carboxyl group 

 may have an influence ; it is worth noting that Warburg observed that 

 leucine ester was hydrolysed by pancreatic juice, but whether this was 

 due to the trypsin or the lipase in the juice was not determined. 



The hydrolysis of leucyl-glycyl-glycine but not of the more com- 

 plex dileucyl-glycyl-glycine was probably due to the configuration of 

 the dileucyl group. 



4. The Nature of the Enzyme. 



In the earlier experiments by Fischer and Bergell it was found that 

 leucyl-alanine was hydrolysed by an extract of pancreas ; it was not, 

 however, hydrolysed by pure pancreatic juice. Such extracts probably 

 contain other enzymes, more especially the autolytic enzyme which 

 produces the hydrolysis ; the later work of Abderhalden and his co- 

 workers upon the action of enzymes from various organs also show that 

 polypeptides not hydrolysed by pure trypsin are attacked by these 

 enzymes (see table, p. 68). 



II. Pepsin. 



Amino acids have been described by various authors as occurring 

 together with the proteoses and peptones in a pepsin digest of proteins. 

 One might have expected that pepsin would act upon certain of the 

 synthetical compounds, especially those most easily hydrolysed by tryp- 

 sin. Pure pepsin, prepared by Pawlow, had no action upon glycyl-1- 

 tyrosine, leucyl-alanine, leucyl-leucine, dialanyl-cystine, and leucyl- 

 glycine. Fischer concluded that the chain of amino acids was not 

 sufficiently long to allow of attack by pepsin. The amino acids 

 obtained by the digestion of proteins probably arise by the action of 

 other enzymes contained in the enzyme solution employed. 



Another explanation of the non-hydrolysis by pepsin may be that it 

 acts upon combinations of amino acids in the form of anhydrides. 



///. Other Enzymes. 



Not only are the synthetical polypeptides hydrolysed by the en- 

 zyme of the pancreas, but they are also hydrolysed by the enzymes 

 occurring in other parts of the animal body. 



It was found by Abderhalden and Bergell, in 1903, that glycyl-gly- 

 cine when subcutaneously introduced into a rabbit was converted into 

 glycine which appeared in the urine, whereas glycine, if administered 

 in a similar way, was completely burnt up and was not excreted. 

 Abderhalden and Rona subsequently showed that glycyl-1-tyrosine was 



