[Electrophoretic Analysis of Abnormal Data on Serum Protein Electrophoresis]

We recently demonstrated glycation of monoclonal IgA and the presence of IgA-albumin complexes, but the significance of the complexes was not clear. We describe a non-diabetic patient with IgA type M-protein whose serum fructosamine and glycoalbumin levels were elevated. On electrophoresis of the serum protein of the patient, the albumin band shifted to the cathode side. The abnormal precipitin arc of IgA-albumin complexes was detected by immunoelectrophoresis. To elucidate the mechanism of IgA-albumin complexes, we analyzed their properties using immunoelectrophoresis, Western blotting, and two-dimensional gel electrophoresis. The macromolecularized albumin spots were demonstrated by two-dimensional Western blotting with antiserum to human albumin of the patient's serum. Moreover, the IgA-albumin complexes were dissociated on treatment with 2-mercaptoethanol. It can be considered that albumin is bound to the monoclonal IgA molecule by covalent disulfide bonds, and that the albumin binding site is located near the hinge region (311Cys) of the IgA molecule and involves the free SH group, thought to be present in the α-chain.