Chemistry of human erythrocyte polylactosamine glycopeptides (erythroglycans) as related to ABH blood group antigenic determinants.
Human erythrocytes bear carbohydrates linked to both proteins and lipids. The majority of the carbohydrates is carried on two proteins: 1) Band 3 (which carries a high molecular weight polylactosamine, variously termed "Erythroglycan", "poly(glycosyl)peptide" or "lactosaminoglycan" and 2) Glycophorin A (which carries 15 O-linked tetrasaccharides and 1 triantennary N-linked structure). The remainder of carbohydrates are carried mainly by a few other glycoproteins (glycophorins B,C, the glucose transporter and others) with a minor amount carried by glycosphingolipids. This report concerns the Band 3 carbohydrate and its content of potential ABH-active sites. We have determined that an average number of two [Fuc1----2Ga11----4GlcNAc] sequences are carried by each "erythroglycan", polylactosamine N-linked oligosaccharide. One such large oligosaccharide occurs on each molecule of Band 3 polypeptide of which there are 1,000,000 copies per erythrocyte. Therefore, about 2,000,000 possible ABH sites are borne by Band 3 on each erythrocyte. This approximates the number of immunologically estimated ABH sites on human erythrocytes. Thus, Band 3 carbohydrate probably carries the majority of ABH substance on human red cells, while other glycoproteins and glycosphingolipids carry a minor fraction.