ANTIGENS 



47 



(4) 

 G1(1-6)G1(1-6)G1(1-6)G1(1-6)G1 



G1(1-6)G1(1-6)G1(1-6)G1(1-4)G1 

 (6) 



Fig. 3-8. Suggested structure of dextran. 



apparent that isomaltose (two glucose units) is distinctly better than 

 glucose as an inhibitor but that isomaltotriose is much better than 

 either, suggesting that the antibody determinant corresponds to an 

 antigenic determinant of at least three glucose units. Actually, the 

 data suggest that the antibodies can distinguish even isomaltohexaose 

 (six glucose units) from any smaller antigenic determinant, but the 

 difference between the pentaose and the hexaose is not great. Kabat 

 suggests that the hexaose is the largest group capable of entering the 

 cavity in the anti-dextran antibody molecule. 



If the hexasaccharide is accepted as the largest group which can 

 totally combine with the combining site of the antibody, the contri- 

 bution of each glucose residue, starting with the terminal unit, to 

 the total free binding energy between antibody and antigen can be 

 computed. Such calculations are shown in Table 3-5, taken from 



::::-s 



GIGIGI 

 (Isomaltotriose) 



GIGIGIGI 

 (Isomaltotetroose) 



GIGIGIGIGI 

 (Isomoltopentaose) 



GIGIGIGIGIGI 

 (Isomaltohexoose) 



Fig. 3-9. Relative inhibitory power of oligosaccharides for anti-dextran serum 

 acting on dextran. (Redrawn from data of Kabat, 1957.) 



