LOCATION OF UBIQUINONE HOMOLOGS IN LIPOSOME MEMBRANES STUDIED BY FLUORESCENCE ANISOTROPY OF DIPHENYL-HEXATRIENE AND TRIMETHYLAMMONIUM-DIPHENYL-HEXATRIENE

The measurements of diphenyl-hexatriene (DPH) and trimethylammonium-di phenyl-hexatriene (TMA-DPH) fluorescence anisotropy in dipalmitoylphos phatidylcholine (DPPC) and egg yolk lecithin (EYL) liposomes containin g different concentrations of various ubiquinone (UQ) homologues have been performed. UQ-4 induced the highest DPH anisotropy increase in DP PC liposomes, whereas for higher UQ homologues the anisotropy was lowe red with the increase of UQ side-chain length. These differences were less pronounced in EYL liposomes. It was concluded that at a higher co ntent in the membranes (3-4 mol%), the short-chain ubiquinones are arr anged parallel to lipid fatty acid chains, whereas long-chain homologu es are progressively removed from the lipid acyl chains into the midpl ane region of the membrane. At the lower (1-2 mol%) concentrations, lo ng-chain quinones seem to be evenly distributed within the membrane, e specially in EYL membranes. UQ-10 in EYL liposomes perturbed TMA-DPH t o a similar extend as the short-chain ubiquinones indicating that UQ-1 0 penetrates the interface regions of the membrane where its redox rea ctions occur. The localization and physical state of UQ-10 in native m embranes is discussed.