THE SYNTHESIS OF THE PROTEINS 43 



The Action of Enzymes upon the Polypeptides. 

 L The Action of 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 poly- 

 peptides. 



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-glycine -\ 



/3-naphthalenesulphoglycyl-d-alanine 



/J-naphthalenesulpho-d-alanyl-glycine j w 



Di-j8-naphthalenesulphotyrosyl-dl-leucine J 



j8-naphthalenesulphoglycyl-l-tyrosine ) 



j8-naphthaleneglycyl-dl-leucine 



Carbethoxyl-glycyl-dl-leucine 



Glycyl-1-tyrosine } were hydrolysed 



Leucyl-alanine 



Alanyl-leucine 



Leucyl-leucine 



from which it was obvious that several factors conditioned the hydrolysis 

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

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

 metrically, 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. 

 Leucyl-1-tyrosine. Leucyl-leucine. 



* Alanyl-glycyl-glycine. Aminobutyryl-glycine. 



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



* These are racemic compounds. 



