The poly(glycosyl) chains of glycoproteins. Characterisation of a novel type of glycoprotein saccharides from human erythrocyte membrane.

Glycopeptides with complex carbohydrate structure were isolated from delipidated human erythrocyte membranes after digestion with pronase. The poly(glycosyl)peptides isolated (apparent molecular weight 4000--13000) are suggested to contain 20--70 sugar residues in an alkali-stable saccharide chain linked through N-acetylglucosamine to asparagine. The main sugar components are galactose and N-acetylglucosamine, which together account for 80% of total sugars. That the compounds isolated are glycopeptides and not glycolipids is concluded from the following findings: only trace amounts of glucose and fatty acids were present, and no long-chain (sphingosine) bases could be detected; on the other hand, the amounts of mannose and amino acids found are compatible with an N-glycosidic poly(glycosyl)peptide structure. The structure of the poly(glycosyl)peptides was studied using methylation analysis, exoglycosidase treatments, acid hydrolysis of the native as well as the N-deacetylated glycopeptides, and chromium trioxide oxidation. The studies indicate that the poly(glycosyl)peptides contain a repeating-3)galactosyl(beta1-4)N-acetylglucosaminyl(beta1-structure with branch points at the C-6 of the galactose residues. The saccharide chains are terminated in N-acetylglucosaminyl, galactosyl, N-acetylneuraminyl(alpha2-3 and 6)galactosyl and fucosyl(alpha1-2)galactosyl residues, and they also contain blood group A and B determinants.