Heterogeneity of asparagine-linked oligosaccharides of five glycosylation sites on immunoglobulin M heavy chain from mineral oil plasmacytoma 104E.

Mouse myeloma immunoglobulin IgM heavy chains were cleaved with cyanogen bromide into nine peptide fragments, four of which contain asparagine-linked sites of glycosylation. Three of these glycopeptides contain a single site located at asparagines 171, 403, and 563 in the sequence of the intact heavy chain. Another glycopeptide contains two sites of glycosylation at asparagines 332 and 364. All sites contain multiple oligosaccharide structures with a trend towards increased processing from the COOH to the NH2 terminus. Structures present at asparagine 563, located only exclusively high mannose oligosaccharides. Asparagine 403, located penultimate to the COOH terminus, has a major component that is of a complex nature but is incompletely processed. Other sites contain predominantly complex structures consisting of biantennary or triantennary branches. The unusual structure found at asparagine 403 contains fucose even though only one branch has been processed to a terminal galactose. These studies suggest that each site has a unique set of heterogeneous oligosaccharides derived from a complex processing system which utilizes a combination of "position completeness" and polypeptide structure to determine final carbohydrate structure.