Fluorescence depolarization studies of phase transition and fluidity in lecithin liposomes containing .ALPHA.-tocopherol.

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  • FUKUZAWA Kenji
    Faculty of Pharmaceutical Sciences, University of Tokushima
  • CHIDA Hisako
    Faculty of Pharmaceutical Sciences, University of Tokushima
  • SUZUKI Asahi
    Department of Applied Chemistry, Faculty of Engineering, University of Tokushima

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  • Fluorescence Dipolarization Studies of Phase Transition and Fluidity in Lecithin Liposomes Containing α-Tocopherol
  • Fluorescence Dipolarization Studies of

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The effects of α-tocopherol and related compounds on the membrane fluidity of liposomes composed of dipalmitoyl-lecithin or egg lecithin were studied by measuring the fluorescence polarization of DPH (1, 6-diphenyl-1, 3, 5-hexatriene), a hydrophobic fluorescent probe distributed in the hydrocarbon region of lipid bilayers. The transition temperature of dipalmitoyl-lecithin liposomes was lowered on incorporation of α-tocopherol into the membranes. A similar effect was observed on incorporation of phytol or phytanic acid into liposomes, but not on incorporation of 2, 2, 5, 7, 8-pentamethyl-l-hydroxychroman as an α-tocopherol model compound (TMC) which lacks an isoprenoid side chain. Above the phase-transition temperatures, incorporation of α-tocopherol or TMC dose-dependently increased the polarization values of DPH in dipalmitoyl-lecithin and egg lecithin liposomes, while incorporation of phytol or phytanic acid had little effect or slightly lowered the polarization. These results suggest that the effect of α-tocopherol in lowering the phase-transition temperature depends on its hydrophobic side chain, and that its effect in decreasing the membrane fluidity above the phase-transition temperature depends on its hydrophylic chroman ring portion. Cholesterol had an effect similar to α-tocopherol on membrane fluidity, αTocopherol and cholesterol had independent effects in increasing the polarization of DPH above the phase-transition temperature when the two compounds were incorporated together into liposomes.

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