88 INTRODUCTION TO IMMUNOCHEMICAL SPFXIFICITY 



galactosylaminoyl-(1^3)-D-galactose (Fig. 7-Z). This suggests that 

 this disaccharide must be very similar to, or possibly identical 

 with, the terminal disaccharide portion of the specific part of the 

 human A substance. (Morgan and Watkins, 1959). 



H,OH 



o-cf-ZV- Acetyl- D-galactosylaminoyI- (I -^3) - D -galactose 

 Fig. 7-Z. 



Kabat and co-workers (1956), also using the inhibition technique, 

 found evidence bearing on the structure of the specific part of the B 

 antigen. Of the monosaccharides present in the molecule, D-galactose 

 was the best inhibitor of anti-B antibodies, but the galactose-containing 

 disaccharide melibiose, the trisaccharide raffinose, and the tetrasac- 

 charide stachyose (Fig. 7-4) inhibited even better than galactose 

 alone (Fig. 7-5). This would have been expected if the specific part 

 of the B antigen consisted of a terminal nonreducing galactose unit 

 joined by an alpha linkage to another sugar unit. That the linkage 

 is alpha is pretty well shown by the fact that a-methylgalactoside 

 inhibits better than galactose, but the /;?-galactoside inhibits not as 

 well (Fig. 7-5). 



Kabat was also able to draw some conclusions about the sugar 

 residue next to galactose in the specific side chain of the B antigen. 

 It could not be glucose, for glucose is not a part of the B molecule. 

 It was not likely to be another galactose, for, if it were, stachyose, 

 which contains a terminal galactose bound by a l-»6 alpha linkage to 

 another galactose, would be a better inhibitor than melibiose or 

 rafBnose, where the sugar next to galactose is glucose. But stachyose 

 is no better an inhibitor than melibiose or raffinose. According to 

 Kabat, A'^-acetylglucosamine is the only remaining possibility for the 

 next-to-terminal sugar in the specific side chain of B antigen. 



