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 a n d 0 respectively. A general formula for the antigens is:(where Fuc is fucose, Gal is galactose, GlcNAc is N-acetylglucosamine and Glc is glucose) with values of y2 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(glycosy1)ceramides (formerly megaloglycolipids). Individual poly(glycosy1)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(glycosy1)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-(glycosy1)ceramides. Branches of poly(glycosy1)ceramides originate from 3 and 6 position of galactopyranosyl residues. The number of branches is proportional to the degree of molecular complexity. In poly(glycosy1)ceramides isolated from A and A2 erythrocytes the branches are terminated with the following structures GalNAc CI 1 +3 [Fuc CI 1 '21 Gal; Fuc CI 1 -i2 Gal and Gal (presumably Gal 1 -+4 GlcNAc). In poly(glycosy1)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(glycosy1)ceramides from A2 erythrocytes the corresponding figures are 0.75, 3.5, and 2.1 respectively.Poly(glycosy1)ceramides from 0 cells comprise about 3.8 H-active structures and 1.8 terminal galactopyranosyl residues. In poly(glycosy1)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 P-galactosidase affects I-activity only slightly.

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The composition and structure of neutral and acidic oligoglycosylceramides, polyglycosylceramides and polyglycosylpeptides were determined in erythrocyte membranes of two patients with congenital dyserythropoietic anaemia type II. In keeping with previous studies we found an elevated accumulation in CDA II erythrocytes of LacCer, Lc3Cer and nLc4Cer. Gb4Cer was elevated in erythrocytes of only one of the two patients tested. In addition we found a significant increase of 6IVNeuAcnLc4Cer ganglioside. Polyglycosylceramides were elevated 6-fold but they resembled those of cord erythrocytes with respect to complexity and the number of side chains. Polyglycosylpeptides of CDA II erythrocytes were decreased 7-fold. These glycopeptides were, however, heterogeneous with respect to branching pattern; the minor fraction was highly branched whereas the major one was more linear in structure. Both polyglycosylceramides and polyglycosylpeptides exhibited high I and i antigenicity. We postulate that the accumulation of glycolipids and underglycosylation of glycoproteins in CDA II membranes results from the prolongation of G1 and possibly M phases of the mitotic cycle of the erythroid cells in which glycolipids are preferentially synthesized.

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