CHEMISTRY OF VIRUS RECEPTORS 



57 



small amounts of galactose (0.7 %), mannose (0.2 %), fucose (0.7 %), and 

 jV-acetylglucosamine (1.0 %) are present (Gottschalk and Ada, 1956; 

 Heimer and Meyer, 1956). By very gentle alkali treatment, Gottschalk (1957c) 

 has detached a disaccharide from BSM. This reducing disaccharide was 

 recently obtained in an analytically pure state; its formula is C 19 H 32 14 N 2 

 and it consists of NANA linked ketosidically to C 6 of iV-acetylgalacto- 

 samine (NAGal), as shown in Fig. 2. The viral enzyme and RDE split the 

 disaccharide into NANA and A T -acetylgalactosamine. (Gottschalk and Graham, 



NHAc 



Neuraminidase 



6-«<-D-N-Acetylneuraminyl-N-acetylQalactosanninc 



Fig. 2. 



1958). By this action the enzyme is characterized as an O-glycosidase 

 (ketosidase). Since both the viral enzyme and RDE invariably release from 

 their substrates a terminal, ketosidically linked, acylated neuraminic acid, 

 the enzyme has been termed "neuraminidase" (Gottschalk, 1957b). 



From the evidence presented it would appear that the soluble influenza 

 virus receptors (hemagglutinin inhibitors) are conjugated proteins with 

 oligosaccharides as prosthetic groups. The size of the oligosaccharide may 

 vary with the type of mucoprotein, and so may vary the number of prosthetic 

 groups. Acetylated neuraminic acid residues are terminal units of the 

 oligosaccharides; these terminal units are joined through a neuraminidase- 

 susceptible glycosidic linkage to an adjacent sugar residue. There is every 



