340 



IMMUNOLOGY 



NH, 



NH, 



I 



c=o 



I 



N— H 



I 

 H— C— COOH 



I 



I 

 c=o 



N— H 



I 

 HOOC— C— H 



Here the mere difference in relative positions of a hydrogen atom 

 and a earboxyl group suffices to alter the serological reactivity. 



Ijandsteiner also succeeded in obtaining immune sera which 

 differentiated sharply the three antigens obtained by coupling 

 dextro-, levo- and meso-tartaric acids to proteins such as horse 

 serum through diazotization of the corresponding p-aminotar- 

 tranilic acids, formulae for which are shown below: 



-NH. 



Position Isomers. — Landsteiner also says that the relative posi- 

 tions of groups are quite important in determining specificity. An 

 example may be seen in a consideration of glycyl-alanine and 

 alanyl-glycine. It would be difficult to differentiate them chemi- 

 cally but they should be biologically unlike since their position 

 relationship.s are different. The glycyl-alanine is formed as fol- 

 lows : 



