Glycoproteins of Cell Surfaces

Abstract The glycoproteins of three different cell surface membranes of the rat have been investigated by acrylamide gel electrophoresis with the use of discontinuous buffers in the presence of sodium dodecyl sulfate (SDS). Liver, kidney brush border, and erythrocyte ghost membranes are solubilized in SDS and after brief exposure to dilute base are reduced with βmercaptoethanol. The gels, after washing free of SDS, are Schiff-stained, and it is demonstrated, by the use of glycoproteins of known molecular weight and subunit composition, that the stained patterns represent size separations of glycoprotein subunits. Each membrane is found to have an identifiable glycoprotein subunit pattern composed of at least 6 to 11 different sized subunits. Most of the staining intensity is present in one to three subunits. Although each membrane has its own unique pattern, liver and kidney brush border have four identically sized subunits. These subunits have molecular weights of 250,000, 195,000, 130,000, and 96,000 when estimated by interpolations of relative mobilities between protein markers. The erythrocyte ghost also contains a 96,000 molecular weight glycoprotein subunit. Sialic acid determinations made on cut gel slices show that all prominent Schiff-positive glycoproteins contain sialic acid.