title: Transbilayer mapping of membrane proteins using membranes isolated on polylysine-coated polyacrylamide beads.
abstract: Erythrocyte and HeLa cell plasma membranes were isolated on polylysine-coated polyacrylamide beads and the transbilayer disposition of their proteins was investigated. When membranes of intact erythrocytes were isolated on beads and then labelled by lactoperoxidase-catalysed iodination, their labelling pattern was similar to that of inside-out vesicles in solution. When the membranes of intact HeLa cells were isolated on beads and then labelled by galactose oxidase-[3H]borohydride treatment, no glycoprotein or glycolipid sugars were accessible. On the other hand, when the HeLa cell membranes were isolated on beads and then labelled by the lactoperoxidase-catalysed iodination, all of the major membrane proteins were iodinated. These experiments confirmed for HeLa cell membranes what had previously been shown for erythrocyte membranes: when the membranes of intact cells are isolated on beads, the accessibility of their surfaces to enzymatic probes is the same as would be expected of inside-out vesicles in suspension. Double-label experiments, in which the HeLa cell membranes were labelled first on the intact HeLa cells and again after isolation on beads, identified several proteins which may span the membrane.
mesh_terms: D001894:Borohydrides; D002462:Cell Membrane / Q000032:analysis; D004910:Erythrocyte Membrane / Q000032:analysis*; D004912:Erythrocytes / Q000032:analysis*; D005692:Galactose Oxidase; D006367:HeLa Cells / Q000032:analysis*; D006801:Humans; D007553:Isotope Labeling; D008051:Lipid Bilayers; D008565:Membrane Proteins / Q000032:analysis* / Q000097:blood; D011107:Polylysine; D014316:Tritium
chemical_list: D001894:Borohydrides; D008051:Lipid Bilayers; D008565:Membrane Proteins; D014316:Tritium; D011107:Polylysine; D005692:Galactose Oxidase