title: Regular surface layer of Azotobacter vinelandii.
abstract: Washing Azotobacter vinelandii UW1 with Burk buffer or heating cells at 42 degrees C exposed a regular surface layer which was effectively visualized by freeze-etch electron microscopy. This layer was composed of tetragonally arranged subunits separated by a center-to-center spacing of approximately 10 nm. Cells washed with distilled water to remove an acidic major outer membrane protein with a molecular weight of 65,000 did not possess the regular surface layer. This protein, designated the S protein, specifically reattached to the surface of distilled-water-washed cells in the presence of the divalent calcium, magnesium, strontium, or beryllium cations. All of these cations except beryllium supported reassembly of the S protein into a regular tetragonal array. Although the surface localization of the S protein has been demonstrated, radioiodination of exposed envelope proteins in whole cells did not confirm this. The labeling behavior of the S protein could be explained on the basis of varying accessibilities of different tyrosine residues to iodination.
mesh_terms: D001395:Azotobacter / Q000648:ultrastructure*; D002413:Cations, Divalent; D002458:Cell Fractionation; D002462:Cell Membrane / Q000648:ultrastructure; D004591:Electrophoresis, Polyacrylamide Gel; D005613:Freeze Etching; D007700:Kinetics; D008565:Membrane Proteins / Q000032:analysis*; D008854:Microscopy, Electron; D008970:Molecular Weight; D009994:Osmolar Concentration; D011485:Protein Binding
chemical_list: D002413:Cations, Divalent; D008565:Membrane Proteins