POLYPEPTIDES 63 



The Action of Enzymes. 



/. Trypsin. 



One of the best proofs that the protein molecule is built up of 

 amino acids coupled together by the methods devised by E. Fischer 

 is given by the action of the various enzymes upon the synthetical 

 polypeptides. 



In 1903, soon after the synthesis of a few of the simple dipeptides 

 and their derivatives had been effected, Fischer and Bergell investigated 

 the action of an extract of pancreas upon them, and they found that 



glycyl-glytine 



0-naphthalenesulphonylglycyl-d-alanine 



0-naphthalenesulphonyl-d-alanyl-glycine 



di-3-naphthalenesulphonyltyroeyl-dl-leucine 



/3-naphthalenesulphonylglycyl-l-tyrosine 



/3-naphthalenesulphonylglycyl-dl-leutine 



carbethoxyl-glycyl-dl-leucine 



glycyl-1-tyrosine 

 leucyl-alanine 

 alanyl-leucine 

 leucyl-leutine 



were hydrolysed 



from which it was obvious that several factors conditioned the hydro- 

 lysis by the enzymes of the pancreas, such as the nature of the dipeptide 

 and its configuration : e.g., the racemic compounds were hydrolysed 

 asymmetrically, the natural component, such as 1-leucine being split off 

 from carbethoxyl-glycyl-dl-leucine, the remainder not being acted upon. 

 The results coincide with the facts known with regard to the rapid 

 separation of leucine and tyrosine from proteins by the action of 

 trypsin ; the other amino acids, such as glycine and alanine, are not 

 obtained during the early stages of digestion. 



Fischer and Abderhalden, in 1905, extended these observations by 

 investigating the effect of pancreatic juice prepared by Pawlow from a 

 pancreatic fistula and activated by enterokinase from duodenal juice, 

 i.e., by the action of pure trypsin upon a larger number of polypeptides, 

 and they were able to divide the polypeptides into two distinct 

 classes : 



Those Hydrolysed. Those not Hydrolysed. 



* Alanyl-glycine. Glycyl-alanine. 



* Alanyl-alanine. Glycyl-glycine. 



* Alanyl-leucine A. Alanyl-leucine B. 



* Leucyl-isoserine A. Leucyl-alanine. 

 Glycyl-1-tyrosine. Leucyl-glycine. 



* These are racemic compounds. 



