Topographical Distribution of Complex Carbohydrates in the Erythrocyte Membrane

Abstract

Abstract Human red blood cell membranes treated with galactose oxidase were specifically labeled in galactose and N-acetylgalactosamine residues by reduction with tritiated borohydride. Ceramide tri- and tetrahexosides were the most intensely reactive lipid species. Several labeled polypeptide peaks were resolved by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. While some of the radioactivity appeared to correspond to known, principal glycoproteins, a major part of the label was distributed in regions of the gel bearing only weakly stained protein and glycoprotein components. The pattern of labeling was essentially the same for intact erythrocytes and unsealed ghosts. Preparations of sealed, inside-out vesicles showed very little labeling, all of which could be attributed to small amounts of contamination from accessible outer surface. On this basis, all of the glycoprotein and glycolipid sugars reactive with galactose oxidase plus tritiated borohydride can be assigned to the external surface of the membrane.