Blood-group A and B determinants are located in different polyglycosyl peptides isolated from human erythrocytes of blood-group AB

Abstract

The distribution of blood-group A and B determinants was studied by isolating blood-group ABH-active polyglycosyl peptides from delipidated human blood-group AB erythrocyte membranes after extensive digestion with pronase followed by chromatography on Bandeiraea simplicifolia I (BsI) lectin coupled to Sepharose. 20% of the polyglycosyl peptides were bound to BsI lectin. The glycopeptides bound were further fractionated using the blood-group-A-specific lectin from Vicia cracca (Vc). Approximately half of these were bound to the Vc lectin. The glycopeptides, which were bound to the Vc column, were not bound to the blood-group-B-specific isolectin from B. simplicifolia (BsIB4) whereas the Vc-unbound glycopeptides readily bound. The results indicate that in the polyglycosyl peptides isolated from AB erythrocytes A and B determinants are located in different carbohydrate chains. The polyglycosyl peptides, which did not bind to BsI lectin, were composed on the average of 30 monosaccharide units and those that bound contained on the average 55 monosaccharide units. The sugar composition was similar in both fractions except that N-acetylgalactosamine was found only in the BsI-bound glycopeptides. The substitution patterns of the monosaccharides were quite similar in both fractions except 2,3-O-linked galactose, which was enriched 7.5-fold in the BsI-bound glycopeptides and 3,6-O-linked galactose, which also enriched in the BsI-bound glycopeptides suggesting that these have a more branched structure than the BsI-unbound glycopeptides. Glycopeptides derived from bands 3 and 4.5 were prepared from A1B-blood-group erythrocyte membranes and fractionated as above. 25% of the glycopeptides were bound to BsI-lectin from both samples. 70% of the BsI-bound material from band 3 was bound to Vc lectin and 60% from band 4.5. The results indicate heterogeneity in the glycosylation of these bands.