Cryptic A‐Like Receptor Sites in Human Erythrocyte Glycoproteins: Proposed Nature of Tn‐Antigen

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Abstract
Periodate oxidation and Smith degradation of desialized human erythrocyte glycoproteins lead to an almost complete destruction of galactose and some loss of galactosamine and glucosamine. Neutral sugar and hexosamine content of native MN substances are only slightly influenced by periodate oxidation. Destruction of galactose is accompanied by an uncovering of A‐like receptor sites detectable by agglutinins from plants and snails, which are directed against terminal N‐acetylgalactosamine. From the specificity of these antibody‐like substances, it is deduced that the amino sugar functioning as receptor is α‐glycosidically linked. Destruction of the receptor sites by subsequent alkaline borohydride treatment suggests that the N‐acetylgalactosamine is unmasked by degradation of the alkali‐labile tetrasaccharide of human erythrocyte glycoproteins. Periodate‐oxidized and Smith‐degraded NANA‐free erythrocyte and ovarian cyst glycoproteins treated by acetolysis are potent inhibitors of anti‐Tn from man, animals, and plants, suggesting that Tn‐antigen is represented by terminal, α‐glycosidic, peptide‐bound N‐acetylgalactosamine. It is concluded that Tn‐antigen is probably a cryptic determinant of the alkali‐labile tetrasaccharide, which has been isolated from human erythrocyte glycopeptides.