Studies on Immunoglobulins by Ultra-high Resolution Scanning Electron Microscopy

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The development of an ultrahigh resolution scanning electron microscope (UHS-Tl) enabled the observation of biological macromolecules. By the SEM immunoglobulin G (IgG) was clearly observed by use of the carbon plate method. The IgG molecules consisted of three spherical bodies which were divided into two parts respectively. The central body corresponded to Fc- fragment and two side bodies were regarded as Fab-fragments.Although the IgG was clearly observed by the carbon plate method, immunoglobulin M (IgM) was very difficult to be observed, because it had very low contrast and was damaged by electron beam very rapidly. For enhancing specimen contrast and avoiding beam damage we developed a heavy metal impregnation method with phosphotungstic acid, uranyl acetate or osmium tetroxide mordanted by tannic acid. By this method IgM was successfully observed. The molecules consisted of a central plate and radially arranged five units which were Y-shaped.In addition, the morphology of IgG conjugated with colloidal goid particles were studied, which were very often used for immunocytochemistry. The IgG appeared sometimes as comlexes of three units and sometimes as V- shaped filamentous structures on the surface of the gold particles.Thus ultrahigh resolution SEM seemed to play an important role for studying immunoglobulins.