Visualization of Charged Groups on the Surface of Rat Liver Nuclei

Anionic groups on the outer surfaces of isolated rat liver nuclei were rendered visible in the electron microscope by staining with colloidal iron hydroxide at different pH values. At pH 1.8 the nuclei did not adsorb particles of stain, although plasma membranes left in the same preparation showed heavy labelling. After pretreatment with neuraminidase at pH 6 the plasma membranes were no longer stained. At pH 3.0 the nuclear surfaces also stained intensely. The staining pattern acquired at this pH did not appear to be changed by neuraminidase pre-treatment. With the staining method used, rat liver nuclear surfaces seemed to have no exposed sialic acid under isolation conditions which preserve the nuclear membranes and leave the ribosomes attached to the nuclear surface. However, at higher pH values other anionic groups seem to become dissociated and are stained with colloidal iron hydroxide.