Isolation and characterization of poly(glycosyl)ceramides (megaloglycolipids) with A, H and I blood-group activities.

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, A2 and O respectively. A general formula for the antigens is: (Fuc)3-4(Gal)n(LlcNAc)n-2(Glc)1(Sphingosine)1(where Fus 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-acetylgalactosamine. 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-Acdtylglucosamine substituted at 3 position was not found in poly(glycosyl)ceramides. Brances of poly(glycosyl)ceramides originate from 3 and 6 position of galactopyranosyl residues. The number of branches is proportional to the degree of molecular complexity. In poly(glycosyl)ceramides isolated from A and A2 erythrocytes the branches are terminated with the following structures GalNAc alpha 1 leads to 3 [Fuc alpha 1 leads to 2] Gal; Fuc alpha 1 leads to 2 Gal and Gal (presumably Gal beta 1 leads to 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 A2 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 beta-galactosidase affects I-activity only slightly.