Monosaccharide composition of human monoclonal (18) and normal (8) IGM immunoglobulins: proposed structural models for their glycan chains.

The carbohydrate composition of 18 monoclonal IgM (Waldenström macroglobulinemia) was determined by gas-liquid chromatography. Two populations occurred with mean sugar contents of 7.3% (12 IgM and 10% (6 IgM). A value of 7.2% was obtained for 8 IgM prepared from 8 normal sera. On the basis of mean molar ratios established for each monosaccharide residue, structural models for oligosaccharide units are proposed. The number of complex glycan chains (N-acetyllactosaminic type) is higher in the 10% population, which would correspond to IgM with a mean sedimentation constant of 18.3So20, W. On the other hand, the 7.3% population has a lower content of "mature" chains and its sedimentation constant would be inferior: 17S)20, W.