CARBOHYDRATE HETEROGENEITY OF HUMAN MYELOMA PROTEINS OF THE IGA1 AND IGA2 SUBCLASSES

Comparative studies of the N-linked carbohydrate chains of human myelo ma proteins of the IgA1 and IgA2 subclasses were performed. The N-link ed carbohydrate chains were released by hydrazinolysis from the polype ptide backbone, converted to radioactive oligosaccharides by sodium bo rotritide reduction after N-acetylation and separated into one neutral and two acidic fractions by paper electrophoresis. The acidic oligosa ccharides were completely converted to neutral oligosaccharides by sia lidase treatment, indicating that they were siayl derivatives. The neu tral and sialidase-treated acidic oligosaccharides were further fracti onated by Bio-Gel P-4 column chromatography. Structural studies of eac h oligosaccharide by sequential exoglycosidase digestion and methylati on analysis revealed that human myeloma IgA proteins contained signifi cant amounts of biantennary complex-type carbohydrate chains in additi on to a small amount of the high mannose-type. The results indicated t hat the oligosaccharide structures of human IgA1 and IgA2 display a hi gh degree of heterogeneity not only in the number of carbohydrate chai ns, but also in their composition.