Location and dynamics of alpha-tocopherol in model phospholipid membranes with different charges.
Studies were made on the position and dynamics of the OH-group of alpha-tocopherol in phospholipid membranes. There was no difference in the spin-lattice (T1) relaxation times at the 5a-position of alpha-tocopherol labeled with 13C- or C19F3-determined from the nuclear magnetic resonance (NMR) spectra of liposomes positively charged with stearylamine (SA) and negatively charged with dicetylphosphate (DCP). The zeta-potentials of egg yolk phosphatidylcholine (EYPC) liposomes with and without SA or DCP were not affected by incorporation of 20 mol% alpha-tocopherol, though incorporation of 10 mol% ascorbyl-palmitate decreased the zeta-potentials of EYPC and EYPC-SA liposomes. The P==O stretching band (1235 cm-1) of the phosphate group and C==O stretching band (1734 cm-1) of the acyl ester linkage in dimyristoylphosphatidylcholine (DMPC) liposomes, measured by Fourier transform-infrared (FT-IR) spectroscopy, were not changed by incorporation of alpha-tocopherol. These results suggest that no specific interaction occurred between the OH-group of alpha-tocopherol and the polar interfacial region of the bilayer. The dynamic quenching effects of n-(N-oxy-4,4'-dimethyloxazolidine-2-yl)stearic acids (n-NSs) on the intrinsic fluorescence of alpha-tocopherol were in the order 5-NS > 7-NS = 12-NS > 16-NS. Acrylamide, a water-soluble fluorescence quencher with a very low capacity to penetrate through phospholipid bilayers, had very low quenching efficiency. These results indicate that the bulk of the chromanol moiety of alpha-tocopherol is located in a position close to that occupied by the nitroxide group of 5-NS in the membranes and is poorly exposed at the membrane surface.(ABSTRACT TRUNCATED AT 250 WORDS)
Fukuzawa
K
K
Faculty of Pharmaceutical Sciences, Tokushima University, Japan.
Ikebata
W
W
Shibata
A
A
Kumadaki
I
I
Sakanaka
T
T
Urano
S
S
D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D016166:Free Radical Scavengers; D008081:Liposomes; D009682:Magnetic Resonance Spectroscopy; D008564:Membrane Potentials; D008567:Membranes, Artificial; D010084:Oxidation-Reduction; D010743:Phospholipids / Q000737:chemistry*; D013113:Spin Labels; D014810:Vitamin E / Q000737:chemistry*
D016166:Free Radical Scavengers; D008081:Liposomes; D008567:Membranes, Artificial; D010743:Phospholipids; D013113:Spin Labels; D014810:Vitamin E