| Summary: | The effects of vitamin E on the activity of membrane-dependent enzymes suggest that it acts indirectly by modifying some properties of the lipid host. The effects of α-tocopherol (α-T) and α-tocopherol hemisuccinate (α-THS) on phospholipid monolayer structure, curvature, and bending elasticity were examined using X-ray diffraction and the osmotic stress method. These ligands were mixed with the hexagonal phase-forming lipid, dioleoylphosphatidylethanolamine (DOPE). Increasing levels up to 50 mol% α-T in DOPE in excess water result in a systematic decrease in the lattice dimension. Analysis of the structural changes imposed by α-T shows that it contributes a spontaneous radius of curvature of −13.7 Å. This unusually negative value is comparable to diacylglycerols. α-T does not affect the bending elasticity of these monolayers. α-THS in its charged form decreases membrane curvature, but in its undissociated neutral form has a qualitatively similar but reduced effect on monolayer curvature, as does α-T.We discuss these results in terms of the local stresses such ligands would produce in the vicinity of a membrane protein, and how one might expect proteins to respond to such stress.
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