ELECTRON MICROSCOPIC LOCALIZATION OF MACROMOLECULES ON MEMBRANE SURFACES

Ferritin-conjugated antibodies and ferritin-conjugated plant agglutinins can be used as specific stains to localize macromolecular antigens and specific saccharide residues, respectively, on membranes. In conjunction with a new procedure for preparing membrane specimens by cytolysis at an air-water interface, specific ferritin-conjugated antibodies have been used to determine the distribution of the Rh₀(D) antigen on human erythrocyte membranes, and of the H-2 histocompatibility alloantigens on murine erythrocytes. Over a period of time these distributions are random, lending support to the lipid-globular protein mosaic model of membrane structure. With ferritin-conjugated plant agglutinins, it has been found, for several types of saccharide residues and several varieties of plasma membranes, that the membrane-bound oligosaccharides are exclusively located on the outer surfaces of the membranes; none is found on the inner cytoplasmic surface. These results strongly suggest that the glycoproteins of membranes do not rotate from the outer to the inner surface at a significant rate under physiological conditions.