Erythroglycan, a High Molecular Weight Glycopeptide with the Repeating Structure [galactosyl-(1 Leads to 4)-2-deoxy-2-acetamido-glucosyl(1 Leads to 3)] Comprising More Than One-third of the Protein-bound Carbohydrate of Human Erythrocyte Stroma

Glycopeptides of molecualr weight range 7,000 to 11,000, unusual in size and structure, have been partially purified from pronase digests of lipid-free human erythrocyte ghosts; we term this fraction "erythroglycan." These substances comprise about one-third of the galactose and glucosamine of the ghost. Methylation analysis of erythroglycan yields mainly 4-linked glucosamine, 3-linked galactose, and 3,6-linked galactose, along with mannose and fucose derivatives. Hydrazinolysis and nitrous acid deamination degrade erythroglycan to galactosyl-2,5-anhydromannose, indicating a repeating structure of galactosyl, (1 leads to 4)-2deoxy-2-acetamidoglucosyl (1 leads to 3). Digestion with the endo-beta-galactosidase from Escherichia freundii gives only partial cleavage of the erythroglycan, probably because of the arborized structure indicated by the branched galactose. Since sphingosine is not detectable after methanolysis by chemical ionization mass spectrometry, and since amino acids are present, we conclude that these substances are probably glycopeptidic in origin and are not "macroglycolipids." Erythroglycan may have the same type of keratan-like core structure as the long chain blood group glycolipids from human erythrocytes and could be a protein-bound carrier of the ABO determinants.