ELECTRON MICROSCOPIC LOCALIZATION OF MACROMOLECULES ON MEMBRANE SURFACES*

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Abstract
Summary: 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.