94 



A. I. RINGER 



CH 2 NH 2 



I 



H CH 3 



\ I 

 CO N CH 



COOH 

 Glycyl-alanin 



CH 3 

 CHNH 2 



H 



\ 

 CO N CH 2 



COOH 

 Alanyl-glycin 



That there is a difference between these two compounds we know from 

 the fact that they behave differently -in their physical property of rotating 

 the plane of polarized light. Glycyl-alanin rotates the plane of polarized 

 light 50 to the left, whereas alanyl-glycin rotates it 50 to the right 

 (Abderhalden and Fodor, 1912). 



In the union of glycocoll, alanin and leucin, we have six different pos- 

 sible combinations, depending upon the position each amino acid occupies 

 in the molecule with reference to the 'other amino acids. That there is 

 a difference between these compounds we know from the fact that they all 

 have a different power of rotating the plane of polarized light : Thus : 



I. Glycyl-alanyl-leucin 



II. Glycyl-leucyl-alanin 



III. Alanyl-glycyl-leucin 



IV. Alanyl-leucyl-glycin 



V. Leucyl-alanyl-glycin 



VI. Leucyl-glycyl-alanin 



20 

 D 



90 

 -60 

 -11 

 -30 

 -17 

 20 



With the increase in the number of amino acids the number of isomers 

 increases tremendously, as the following table taken from Abderhalden 

 shows : 



Number of amino acids 



2 

 3 

 4 

 5 

 6 

 7 

 8 

 9 



Number of possible compounds 



2 

 6 



24 



120 



720 



5,040 



40,320 



362,880 



