THE TRANSMEMBRANE GRADIENT OF THE DIELECTRIC-CONSTANT INFLUENCES THE DPH LIFETIME DISTRIBUTION

The fluorescence Lifetime distribution of 1,6-diphenyl-1,3,5-hexatrien e (DPH) and -(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DP H) in egg-phosphatidylcholine liposomes was measured in normal and hea vy water. The lower dielectric constant (by similar to 12%) of heavy w ater compared with normal water was employed to provide direct evidenc e that the drop of the dielectric constant along the membrane normal s hifts the centers of the distribution of both DPH and TMA-DPH to highe r values and sharpens the widths of the distribution. The profile of t he dielectric constant along the membrane normal was not found to be a linear gradient (in contrast to [1]) but a more complex function. Pre sence of cholesterol in liposomes further shifted the center of the di stributions to higher value and sharpened them. In addition, it result ed in a more gradient-like profile of the dielectric constant (i. e. l inearization) along the normal of the membrane. The effect of the chan ge of dielectric constant on the membrane proteins is discussed.