Glycophorin A was purified from the erythrocyte membranes of blood group Cad, Sd(a+) and Sd(a-) donors and the oligosaccharide alditols, obtained after alkaline borohydride degradation, separated by h.p.l.c. on an alkylamine silica gel column, were characterized by sugar analysis. Structure determination of the major acid components by methylation analysis, g.l.c.-m.s. and 1H-n.m.r. indicated that the three blood group Cad red cells under study (samples Cad., Bui. and Des.) carry the same pentasaccharide GalNAc(beta 1-4)[NeuAc(alpha 2-3)]Gal(beta 1-3)[NeuAc(alpha 2-6)]GalNAc -ol(Cad determinant) but in different amounts. This pentasaccharide, however, was absent from glycophorin A of Sd(a+) and Sd (a-) donors, suggesting that the Sda determinant is not associated with glycophorins. It was calculated that glycophorin A from the original Cad donor (Cad.) carries about 12 O-glycosidically linked pentasaccharide chains per molecule whereas only 2-3 of these chains were present in the samples from the two other unrelated Cad individuals (Bui. and Des.) It is well known from quantitative agglutination studies that the proportion of red cells which can be agglutinated by the Dolichos biflorus lectin varies from one Cad blood sample to another. Some are completely agglutinated (Cad. donor) whereas others are only partially agglutinated (Bui. and Des. donors) suggesting that some red cells might not carry the Cad determinants. From the results presented above and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis studies it is suggested that Cad red cells from Bui. and Des. do not carry a mixture of glycophorin A molecules with or without the Cad pentasaccharides but a spectrum of glycoprotein molecules with varying amounts of Cad determinants.

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