| Abstract | Natural, 2R,4′R,8′R-α-tocopherol (vitamin E), labelled selectively with 13C in the methyl group at position 5, was incorporated into unilamellar vesicles of egg phosphatidylcholine. The vesicles are impermeable to the shift reagent Pr3+ and, in the presence of this reagent, separate 13C resonances due to labelled α-tocopherol in the outer and inner monolayers could be observed with relative intensities, 2:1. Subsequent addition of the relaxation reagent Gd2+ causes broadening and greatly shortened spin-lattice relaxation times for the resonance due to α-tocopherol in the outer monolayer only. These data confirm that α-tocopherol is located in both halves of the bilayers with its more hydrophilic chroman moiety very near the lipid-water interface, and indicate that the methyl group at position 5 of the α-tocopherol in the inner monolayer must be at least 40 Å from the aqueous interface of the outer monolayer. © 1985. |
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