The carbohydrate units of asialo-ovomucoid: structural features

The structural features of a heterogeneous glycopeptide fraction from asialo-ovomucoid have been investigated by methylation analysis of the fraction and of products obtained at each stage of its sequential degradation with exo-glycosidases. All glycopeptides in the fraction had a common core-structure beta-D-GlcpNAc-(1 leads to 4)-[beta-D-GlcpNAc-(1 leads to 2)]-alpha-D-Manp-(1 leads to 3)-[beta-D-GlcpNAc-(1 leads to 4)]-[beta-D-GlcpNAc-(1 leads to 2)-alpha-D-Manp-(1 leads to 6)]-beta-D-Manp-(1 leads to 4)-beta-D-GlcpNAc-(1 leads to 4)-beta-D-GlcpNAc leads to Asn. Heterogeneity in the fraction arose from variation in the amount of terminal galactose attached via a hexosaminyl residue to the alpha-D-Manp-(1 leads to 3) residue, and from limited variation in the number of terminal hexosaminyl groups attached to the alpha-D-Manp-(1 leads to 6) residue. One glycopeptide in the fraction contained the unusual feature of two different, triply-substituted mannosyl residues. Other structural features of the glycopeptide are discussed.