Use of Rotofor in two‐dimensional electrophoretic analysis: Identification of a 100 kDa monoclonal IgG heavy chain in myeloma serum

After preparative nondenaturing isoelectric focusing in a Rotofor of 1 mL human serum which showed on two‐dimensional electrophoresis a monoclonal kappa light chain p I < 5.0, the monoclonal kappa light chain was identified in the tubes with pH 7.29 – pH 6.96, indicating that the chain was not free and was most likely part of an immunoglobulin molecule. The combined fractions of the Rotofor were concentrated back to 1 mL and aliquots were separated by two‐dimensional electrophoresis, followed by Western blotting. Enzyme immunoassay of the blot with A′ human IgG (γ chain specific) revealed a monoclonal heavy chain at a molecular size of approximately 100 kDa. Diffuse areas at 50 kDa (the attributed size of γ heavy chain), 100 kDa, and 150 kDa were stained also, but the strong, restricted (picket fence) bands indicating a monoclonal pattern were at 100 kDa. The monoclonal light chain appears to be part of a large or dimeric IgG molecule.