A unique IgG myeloma immunoglobulin molecular weight and other properties

Abstract Molecular weight and some other physicochemical properties of a unique myeloma immunoglobulin, designated IgG(Ud) are presented in the paper. The experiments were performed in a comparative way taking IgG as the standard protein. Molecular weight was determined by ultracentrifugation, Sephadex gel filtration and disc electrophoresis in sodium dodecyl sulphate solution. Molecular weight of IgG(Ud), and fragments F(ab′) 2 Ud and Fab Ud was found to be higher than that of IgG and its corresponding fragments, and for IgG(Ud) appeared to be approx. 176 000. The entire difference was accounted for solely by the Fab Ud fragment, which differs from Fab of IgG by about 8000. Both the light chain and Fd portion appeared to participate equally in the increment of molecular weight. Assuming correct interpretation of the experiments, the increment of molecular weight may be attributed to longer L chain and Fd portion. Amino acid analysis of IgG(Ud) showed higher content of tyrosine, lysine, glutamic acid and valine, and lower content of proline and phenylalanine. The elongation of polypeptide chain, as well as the difference in amino acid composition were supposed to result from unequal crossing-over.