Microheterogeneity of serum myeloma immunoglobulins revealed by a technique of high resolution two-dimensional electrophoresis

A simplified technique of high resolution two‐dimensional electrophoresis has been used to investigate heterogeneity of human serum myeloma proteins. Three types of microheterogeneity have been detected. The heavy chains of IgA, IgM and IgD myeloma proteins demonstrate charge heterogeneity which is far less extensive following neuraminidase treatment and is therefore largely due to sialic acid. The underlying charge heterogeneity, which is apparently resistant to neuraminidase, resembles the charge heterogeneity demonstrated by the heavy chains of IgG myeloma proteins which show no response to neuraminidase treatment. The third type of microheterogeneity is most clearly demonstrated by the heavy chains of IgD myeloma proteins which exhibit heterogeneity with respect to small variations (∼︁3000) in molecular weight. This type of heterogeneity has also been observed, to a lesser extent, in the heavy chain of IgM and IgA myeloma proteins.