CARBOHYDRATE CONTENT OF FRAGMENTS AND POLYPEPTIDE CHAINS OF HUMAN GAMMAG-MYELOMA PROTEINS OF DIFFERENT HEAVY-CHAIN SUBCLASSES

The carbohydrate composition and its distribution within the polypeptide chains and enzymatic fragments of γG-myeloma proteins of different subclasses have been determined; 29% of 76 proteins studied had a hexose content higher than 19 moles/ mole of protein compared to values ranging from 9 to 13 moles of hexose/mole of protein in the remaining 71%. No correlation was observed between hexose content and antigenic subclass of heavy- or light-chain type. The excess carbohydrate on the high carbohydrate-containing proteins was localized to the Fab fragment whereas the Fc fragment contained the same amounts of carbohydrate as that found in normal γG-globulin. Detailed analysis of nine proteins with high carbohydrate content localized the Fab carbohydrate to the Fd fragment in three proteins and to the light chains in four proteins, and in two instances both Fd fragment and light chains contained carbohydrate. Comparable amounts of hexose, glucosamine, and fucose were present in the Fab carbohydrate as was present in the Fc carbohydrate, but the sialic acid content was four times as high in the Fab fragment. No evidence was obtained for the presence of a glycopeptide in the F(ab′)2 fragment which was not in the Fab fragment. Starch gel electrophoretic banding of γG-myeloma proteins was not correlated with carbohydrate content. In one case, however, the banding of the isolated light chains was shown to be due to variations in sialic acid content. © 1968, American Chemical Society. All rights reserved.