Primary structure of N‐glycosidically linked asialoglycans of secretory immunoglobulins from human milk

The asialoglycopeptides obtained from secretory immunoglobulins A from human milk have been separated by gel filtration and affinity chromatography on Concanavalin A‐Sepharose and Lens culinaris agglutinin‐Sepharose columns. Their structures have been determined by sugar analysis, methylation studies including mass spectrometry and 500‐MHz 1H‐NMR spectroscopy. The glycans are of the biantennary N‐acetyllactosamine type differing in their degree of extension by fucosyl‐N‐acetyllactosamine residues. The overall structures of the glycopeptides are as follows: Most of the asialoglycospeptide structures possess an intersecting GlcNAc residue; they are suggested to be located on the α chain of the secretory immunoglobulins A of human milk. The non‐interesected structures probably occur on the secretory piece. The methodology applied to the structural analysis adequately coped with the exteremely high degree of heterogeneity shown by the structures.