Investigations on the oligosaccharide units of an A myeloma globulin

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Abstract
The carbohydrate content of an A myeloma globulin was investigated. The carbohydrate content was unchanged when the protein was isolated from the patient over a period of 18 months. The various polymeric forms of the protein contained similar proportions of carbohydrate. The A myeloma globulin contained approximately 2 residues of 6-deoxy-L-galactose (L-fucose), 14-15 of D-mannose, 12-13 ofD-galactose, 12-13 of 2-acetamido-2-deoxy-D-glucose (N-acetyl-D-glucosamine), 6 of 2-acetamido-2-deoxy-Dgalactose (N-acetyl-D-galactosamine) and 5 of N-acetylneuraminic acid (sialic acid), and these were distributed between 6 oligosaccharide units all of which were present on the heavy polypeptide chains. The oligosaccharide units showed 2 kinds of heterogeneity, termed central and peripheral. Central heterogeneity was shown by the presence of 3 completely different core units, which had the following compositions: 3 residues of D-galactose and 3 of 2-acetamido-2-deoxy-D-galactose, joined to protein by an O-glycosidic linkage between acetamidohexose and serine; 3 residues of D-mannose, 2 of -galactose and 3 of 2-acetamido-2-deoxy-D-glucose, joined to protein by an N-glycosidic linkage between acetamidohexose and aspartic acid; 4 residues of D-mannose and 3 of 2-acetamido-2-deoxy-D-glucose with a linkage similar to that in (the 2nd core unit). The core oligosaccharide units showed peripheral heterogeneity in the attachment of 6-deoxy-L-galactose, 2-acetamido-2-deoxy-D-glucose and N-acetylneuraminic acid. Tentative structures are proposed for these various types of oligosaccharide unit. Glycopeptides were isolated in which the sialic acid content exceeded that of D-galactose. Explanations are given for the electrophoretic mobility and staining characteristics of the various glycopeptides.