296 Biological Chemistry. 



have prepared synthetically a large number of polypeptides 

 of smaller complexity than the proteins ; on these the 

 action of various proteoclastic enzymes has been investi- 

 gated. As some of the amino-acids contain an asymmetric 

 carbon atom, they can be obtained in optically active 

 forms, and it has been found that the stereochemieal con- 

 figuration of the acids is by no means a matter of 

 indifference as regards the action of the enzymes on the 

 polypeptides formed from them. In the following table 

 are given the results of the action of trypsin on some 

 examples of the synthetically-obtained polypeptides : 



Those Hydrolyzed. Those Not Hydrolyzed. 



Alanyl-glycine. Glycyl-alanine. 



Alanyl-leucine. Glycyl-glycine. 



(Racemic) Alanyl-leucine A. (Racemic) Alanyl-leucine B. 



Glycyl-Z-tyrorine. Leucyl-glycine. 



c?-Alanyl-c?-alanine. c?-Alanyl-7-alanine. 



Z-Leucyl-Meucine. Z-Leucyl-c-leucine. 



c?-Leucyl-Weuciiie. 



It will be seen from the above table that some substances, 

 which are chemically very similar, behave in different 

 manner as regards the action of trypsin. Glycyl-alanine, 

 NH 2 -CH 2 -CO NH-CH(CH 3 )-COOH, for example, is not 

 hydrolyzed, whereas the isomeric form alanyl-glycine, 

 NH 2 -CH(CH 3 )-CO NH-CH 2 -COOH, is. Two racemic 

 forms of alanyl-leucine are known. These are 



c?-alanyl-Z-leucine \ d / Z-alanyl--leucine 



Z-alanyl-cMeucine j ( c/-alanyl-c?-leucine 



both of which should be inactive by external compensation. 

 It is noteworthy that these two substances behave differ- 

 ently towards trypsin. The effect of the trypsin is in all 

 cases where it acts to hydrolyze the polypeptide into the 

 mixture of amino-acids ; thus glycyl-alanine and alanyl- 



