title: Possible association of segregated lipid domains of Mycoplasma gallisepticum membranes with cell resistance to osmotic lysis.
abstract: Freeze-fracturing of cholesterol-rich Mycoplasma gallisepticum membranes from cells grown in a medium containing horse serum revealed particle-free patches. The patches appeared in cells quenched from either 4 or 37 degrees C. Particle-free patches also occurred in membranes of cells grown in a serum-free medium supplemented with egg-phosphatidylcholine but not in membranes of cells grown with dioleoylphosphatidylcholine. The appearance of particle-free patches was attributed to the presence of disaturated phosphatidylcholine (PC) molecules in M. gallisepticum membranes, which were synthesized by the insertion of a saturated fatty acid at position 2 of lysophosphatidylcholine derived from exogenous PC present in the growth medium. Consequences of the synthesis of the disaturated PC also included a decrease in osmotic fragility and the ability of the cells to be permeated by K+. Electron paramagnetic resonance and fluorescence polarization measurements revealed that the fluidity of the lipid domain in the protein-rich M. gallisepticum membranes was almost identical to that of an aqueous dispersion of M. gallisepticum membrane lipids. Furthermore, the electron paramagnetic resonance spectra of the membranes were single-component spectra showing no indication of immobilized regions. The possibility that the osmotic resistance of M. gallisepticum cells is associated with the particle-free patches rather than with a restricted membrane fluidity caused by membrane proteins is discussed.
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis / Q000502:physiology; D002462:Cell Membrane / Q000648:ultrastructure; D008560:Membrane Fluidity; D008563:Membrane Lipids / Q000032:analysis / Q000502:physiology*; D008565:Membrane Proteins / Q000032:analysis / Q000502:physiology; D009174:Mycoplasma / Q000032:analysis / Q000502:physiology* / Q000648:ultrastructure; D009996:Osmotic Fragility; D010713:Phosphatidylcholines / Q000502:physiology*; D014783:Viscosity
chemical_list: D001426:Bacterial Proteins; D008563:Membrane Lipids; D008565:Membrane Proteins; D010713:Phosphatidylcholines