ACTION OF THE ENZYMES. 141 



and with him of EMIL ABDERHALDEN 1 and their pupils, on the 

 chemical synthesis of proteins. Even though no more than 

 perhaps a few of the methods employed by these workers 

 to bring about these syntheses are of a character which we 

 can imagine as possible within living cells, this work must 

 for all time furnish the foundation upon which further ad- 

 vances in the chemistry and physiology of the proteins must 

 build. 



Proceeding on the hypothesis that the protein molecule rep- 

 resents a long series of amino-acids chemically joined to each 

 other in various combinations, EMIL FISCHER showed that it is 

 possible to link two or more amino-acids together and obtain 

 a series of chemically more complex compounds known as 

 peptides. If, for example, one molecule of glycocoll is com- 

 bined with a second molecule of the same substance the 

 dipeptide glycyl-glycin is obtained. In a similar way leucyl- 

 leucin can be obtained through the union of two molecules 

 of leucin, and alanyl-alanin from the union of two of alanin. 

 All these are dipeptides. It is possible, however, to make 

 three, four, five, six, etc., amino-acid molecules enter into 

 chemical combination with each other and so obtain tri-, 

 tetra-, penta-, hexa-, or polypeptides. A large number of 

 such peptides have been prepared, as examples of which the 

 following may be cited : 2 



Dipeptides: Glycyl-alanin, alanyl-glycin, alanyl-leucin, 

 leucyl-glycin, glycyl-ty rosin, leucyl-prolin, etc. 



Tripeptides: Leucyl-glycyl-glycin, leucyl-alanyl-alanin. 



Tetrapeptides : Tetraglycin, dileucyl-glycyl-glycin, dialanyl- 

 cystin. 



Penta peptides : Pentaglycin, leucyl-tetraglycin. 



The means by which such syntheses are accomplished are 

 various, and the number of combinations possible very great. 

 Let us ask now whether they are of more than chemical in- 



1 See ABDERHALDEN'S excellent Lehrbuch d. physiol. Chemie, Berlin, 

 1906, Eiweissstoffe. 



2 ABDERHALDEN: 1. c., p. 196. 



