Isolation and Characterization of Poly(glycosyl)ceramides (Megaloglycolipids) with A, H and I Blood‐Group Activities

Abstract

Very complex glycosphingolipids with A, H and I blood‐group activities were isolated from human erythrocyte membranes. The membranes were obtained from erythrocytes of blood group A, A 2 and O respectively. A general formula for the antigens is: (Fuc)3–4(Gal)n(GlcNAc)n–2(Glc)1(Sphingosine)1 (where Fuc is fucose, Gal is galactose, GlcNAc is N‐acetylglucosamine and Glc is glucose) with values of n ranging from 10–27. A‐active preparations contain additionally 2–3 residues of N‐acetyl‐galactosamine. In view of the unusual complexity of these compounds they were designated poly(glycosyl)ceramides (formerly megaloglycolipids). Individual poly(glycosyl)ceramide fractions were isolated from A erythrocytes and were found to differ by about 8 glycosyl residues per molecule forming a series of compounds with 22, 30, 38, 51 and 59 glycosyl residues per mole. Structural studies indicate that the main sequence of poly(glycosyl)ceramides consists of the residues of galactopyranose and 2‐deoxy‐2‐acetamidoglucopyranose substituted at 3 and 4 position respectively. These residues are probably alternating. N‐Acetylglucosamine substituted at 3 position was not found in poly‐(glycosyl)ceramides. Branches of poly(glycosyl)ceramides originate from 3 and 6 position of galacto‐pyranosyl residues. The number of branches is proportional to the degree of molecular complexity. In poly(glycosyl)ceramides isolated from A and A 2 erythrocytes the branches are terminated with the following structures GalNAc α 1→3 [Fuc α 1→2] Gal; Fuc α 1→2 Gal and Gal (presumably Gal β 1→4 GlcNAc). In poly(glycosyl)ceramides from A cells the total number of A and H‐active structures per average molecule of 30–35 glycosyl residues amounts to 2.1 and 1.2 respectively while the number of terminal galactose structures is 1.8. For poly(glycosyl)ceramides from A 2 erythrocytes the corresponding figures are 0.75, 3.5, and 2.1 respectively. Poly(glycosyl)ceramides from O cells comprise about 3.8 H‐active structures and 1.8 terminal galactopyranosyl residues. In poly(glycosyl)ceramides with high “n” values the number of terminal galactose structures is increased. These fractions display high blood‐group I activity. However, the removal of terminal galactose with β‐galactosidase affects I‐activity only slightly.