24 INTRODUCTION TO IMMUNOCHEMICAL SPECIFICITY 



As long as we remember that such projections must not be taken out 

 of the plane of the paper, no incorrect conclusions will be drawn from 

 their use. 



Organic compounds differing in the spatial arrangement of the 

 four different groups attached to a carbon atom have the same chemi- 

 cal and physical properties but differ in their effect on polarized light. 

 Therefore, they are said to be optical isomers. An example of such 

 an optically isomeric compound is aminobenzoylphenylaminoacetic 

 acid, which exists in two forms. One, the d form, rotates the plane 

 of polarized light to the right. The other, the / form, rotates it to the 

 left (Fig. 2-8). 



H COOH 



Hon/ \— conhc— / \ h.n/ \— conhc— / \ 



COOH H 



rf-/)-aminobenzoylphenylamino- /-/)-aminobenzoylphenylamino- 



acetic acid acetic acid 



Fig. 2-8. 



Containing an aromatic amino group, these compounds can be 

 diazotized, coupled to proteins, and made to function as haptens. 

 Since optical isomerism plays a very important role in biochemistry, 

 we would expect that antibodies would be able to distinguish these 

 two isomeric haptens. In fact, Landsteiner and van der Scheer (1928) 

 found that, although the undiluted antigens gave some cross-reaction, 

 they reacted quite specificially when diluted one to one hundred 

 (1:100). 



In later work Landsteiner and van der Scheer (1929) showed that 

 D- and L-tartaric acid (Table 2-4), where two asymmetric carbon 

 atoms are involved, could be differentiated by the appropriate anti- 

 bodies and that both were distinguishable from the "internally com- 

 pensated" mesotartaric acid. 



Next to proteins, polysaccharides are the most important natural 

 antigens. It was therefore logical to ask if isomers of sugars which 

 differ in the configuration of one or more carbon atoms and are not 

 necessarily optical antipodes could be distinguished by antibodies. 

 Goebel and Avery (1929) showed that the monosascharides D-glucose 

 and D-galactose, which differ only in the configuration of the fourth 



