BLOOD GROUP ANTIGENS 87 



ment of the component parts. In fact, recent evidence suggests that 

 only certain parts of the complex polysaccharide molecules are re- 

 sponsible for the specific serological properties. 



Of all the sugars present in the H blood group substance, for ex- 

 ample, only L-fucose (Fig. 7-1) specifically inhibited the agglutinat- 



Fig. 7-1. 



ing action of an anti-H from eel serum. Similar results were obtained 

 with an anti-H of plant origin, of the seeds of Lotus tetragonolobus. 

 It was also found that anti-H from either of these two sources was 

 inhibited more strongly by a-methyl-L-fucopyranoside than by the 

 yt?-furanoside or by fucose alone. These results suggested that l- 

 fucose is an important part of the H substance molecule ; by analogy 

 with Landsteiner's findings with composite haptens (p. 40), L-fucose 

 is probably the terminal group of the specific part. The fact that the 

 a-methylfucopyranoside inhibited better than the /8-methylpyranoside 

 suggested that the fucose was connected by an alpha linkage to the 

 next residue of the reactive portion of the H molecule. 



The first information concerning the role of a particular sugar in 

 the specificity of the A substance was obtained by tests on anti-A 

 reagents of plant origin (Morgan and Watkins, 1959). Anti-A lectins 

 were specifically inhibited by A^-acetylgalactosamine (Fig. 7-2). 

 Most of the human anti-A reagents tested were not inhibited by this 

 amino sugar but were inhibited by the disaccharide 0-a-A^-acetyl-D- 



H NHCOCH3 



A/- Acetyl - D-galacfosamine 



Fig. 7-2. 



