Biochemical characterization of a human spermatozoal sialoglycoprotein with respect to antigenicity masking by its sialic acid moieties.

Four O-glycosidic oligosaccharides (I, II, III, IV) were purified from a human spermatozoal sialoglycoprotein antigen following quantitative beta-elimination and reduction of the linkage sugar by KHB4+. The four oligosaccharides showed a similar carbohydrate composition consisting of sialic acids, galactose, fucose, galactosamine and N-acetylgalactosamine, except for the lack of fucose in II. The linkage sugar was identified as N-acetylgalactosamine at a molar ratio of 23.8 to 1 glycoprotein. The sialic acid moieties of the oligosaccharides were tentatively identified by gas-liquid chromatography following trimethylsilylation. A biological function for these sialic acids is suggested by a significantly increased antibody binding after desialization, as compared to the intact sialoglycoprotein molecule. This masking effect of the sialic acids could raise important questions about the etiology of the naturally occurring antispermatozoal antibodies in sera of sterile man, about which is little known.