Primary structure of two sialylated triantennary glycans from human serotransferrin

Glycopeptides obtained from human serotransferrin by pronase digestion were separated into two fractions by affinity chromatography on Con A-Sepharose. The retarded fraction (85% of total glycopeptides) contained sialylated biantennary glycans of the N-acetyllactosaminic type, the primary structure of which has been previously determined. The non-retained fraction (15% of total glycopeptides) consisted of two isomeric triantennary glycans of the N-acetyllactosaminic type. The primary structure have been elucidated by methylation analysis and 500 MHz 1H-NMR spectroscopy. Both contain an additional NeuAc(alpha2 ¨ 3)Gal(beta ¨ 4)GlcNAc antenna. The latter is linked to C-4 of the (alpha1¨3) bound Man residue in 45% of the glycans in the non-retained fraction but to C-6 of the (alpha1 ¨ 6) bound Man residue, in the remaining 55% of the glycans in this fraction