Human pathologic IgM glycopeptides. Evidence for a very high mannose content glycopeptide

Calorimetric study of the binding reaction of concanavalin A with immunoglublins

The thermal effects associated with the binding reaction of concanavalin A and immunoglobulins have been measured by calorimetry. IgG solutions do not generate heat on mixing with concanavalin A, confirming the low reactivity of IgG for the lectin molecule. IgM solutions, on the other hand, show a substantial enthalpic contribution of delta H = -24 +/- 1kJ/site for the binding reaction between the polysaccharide chains of human IgM macroglobulin and concanavalin. A stoichiometry is 10 monovalent concanavalin A molecules per intact macroglobulin and two bivalent concanavalin A molecules per two sites on the heavy chain of the reduced macroglobulin subunit.

Localization and overall structure of a mannose-rich glycopeptide from a pathologic immunoglobulin

The structure of a mannose-rich glycopeptide from a human pathological IgM has been investigated. It belongs to the group I (simple) glycopeptides and contains only mannose and N-acetylglucosamine residues in a molar ratio of 10:2. The structures of its oligosaccharide moiety and peptide chain have been determined: its molecular localization is specified and the relation between its biosynthesis and the oligosaccharide structure determine is discussed. Based on the alpha- and beta-mannosidase digestions and permethylation studies for the oligosaccharide moiety, and on the results obtained after sequential analysis of the peptide chain, the following structure is proposed for the mannose-rich IgM Du glycopeptide: (Formula: see text). The recovery of one molecule of this glycopeptide per molecule of heavy chain and the determination of the amino acid sequence have led us to locate this glycopeptide on asparagine 402 of the Fc portion of the heavy chain mu of IgM Du.