The carbohydrate units of ovalbumin: Complete structures of three glycopeptides

Three glycopeptides, obtained in quantity from ovalbumin by exhaustive digestion with Pronase and purified by ion-exchange chromatography and gel filtration, had mannose-2-acetamido-2-deoxyglucose-aspartic acid ratios of 5:4:1, 6:2:1, and 5:2:1. The structures of the glycopeptides have been investigated by sequential digestion with purified exo-glycosidases, Smith degradation, and selective acetolysis, and by methylation analysis of the glycopeptides and their degradation products. The resulting data indicated the structures to be α-d-Manp-(1→6)-α-d- Manp-(1→3)]-α-d-Manp-(1→6)-β-d-GlcNAcp-(1→4)]-β-d-GlcNAcp-(1→2)-α-d- Manp-(1→3)]-β-d-Manp-(1→4)-β-d-GlcNAcp-(1→4)-β-d-GlcNAcp→Asn, α-d- Manp-(1→6)-α-d-Manp-(1→3)]-α-d-Manp-(1→6)-α-d-Manp-(1→2)-α-d-Manp- (1→3)]-β-d-Manp-(1→4)-β-d-GlcNAcp-(1→4)-β-d-GlcNAcp→Asn, and α-d-Manp- (1→6)-α-d-Manp-(1→3)]-α-d-Manp-(1→6)-α-d-Manp-(1→3)]-β-d-Manp-(1→4)- β-d-GlcNAcp-(1→4)-β-d-GlcNAcp→Asn. The glycopeptides had a common-core structure consisting of five mannose and two hexosamine residues, but the two larger glycopeptides were not homologous.