Fluorescence probe studies of the interaction of ubiquinone-10 and ubiquinol-10 with phosphatidylcholine bilayers.

Ubiquinone-10 and ubiquinol-10 were incorporated into dipalmitoylphosphatidylcholine vesicles and their interaction with the phospholipids was monitored by fluorescence measurements of diphenylhexatriene used as a probe. It was found that ubiquinone-10 did not perturb the phospholipid thermotropic pretransition but ubiquinol-10 was able to do so. Although, in ethanolic solution, ubiquinone-10 was a better quencher of diphenylhexatriene than ubiquinol-10, when incorporated into phospholipid multibilayers and at temperatures above Tc, ubiquinone-10 produced a smaller decrease in the intensity of the fluorescence probe than ubiquinol-10. Furthermore, the fluorescence anisotropy of the probe was significantly increased by ubiquinol-10 but not by ubiquinone-10. It was concluded that both forms of coenzyme Q have different localizations in the phospholipid bilayer.