Comparison of alkal-labile oligosaccharide chains of M and N blood-group glycopeptides from human erythrocyte membrane

Abstract

Alkali-borohydride degradation of M or N blood-group active, tryptic glycopeptides and glycoproteins was performed under conditions giving the reduced oligosaccharides in a yield significantly improved over that reported earlier. Degradation of desialosylated glycoproteins yielded beta-D-Galp-(1 leads to 3)-D-GalNAcol, D-GalNA-col, and Galol in a ratio of approximately 30:1:1. GalNAc was shown to be alpha-D-linked to the polypeptide chain. Degradation of the glycopeptides gave the tetrasaccharide, NeuAc-(2 leads to 3)-beta-D-Galp-(leads to 3)-[NeuAc-(2 leads to 6)]-D-GalNAcol, and two trisaccharides, NeuAc-(2 leads to 3)-beta-D-Galp-(1 leads to 3)-D-GalNAcol and beta-D-Galp-(1 leads to 3)-[NeuAc-(2 leads to 6)]-D-GalNAcol, in a molar ratio of approximately 8:3:1. These oligosaccharides were accompanied by minor amounts of unidentified compounds showing identical electrophoretic mobility when derived from M and N glycopeptides. During isolation of the reduced oligosaccharides, the release of sialic acid did not exceed 5.5%, indicating that only a part of the trisaccharide portion might have arisen as a result of desialosylation of the tetrasaccharide. No differences between the degradation products derived from M and N glycoproteins were found, and the presence of significant amounts of larger, alkali-labile oligosaccharides was not observed.