The fidelity of response by 1-[4-(trimethylammonio)phenyl]-6-phenyl-1,3,5-hexatriene in time-resolved fluorescence anisotropy measurements on lipid vesicles

Abstract

Time-resolved fluorescence anisotropy measurements on 1-[4-(tri-methylammonio)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) molecules in lipid vesicles of palmitoyloleoylphosphatidylcholine (POPC), PC extracted from egg yolk (EggPC), dioleoyl-PC (DOPC), dilinoleoyl-PC (DLPC), phosphatidylglycerol extracted from egg yolk (EggPG), dioleoyl-PG (DOPG), sulfoquinovosyldiacylglycerol (SQDG) and digalactosyl-DG (DGDG) with and without cholesterol are presented. The observed intensity decay curves are analyzed simultaneously in terms of the Brownian rotational diffusion model. The analysis thus yields the isotropic fluorescence decay, the initial anisotropy r (0), the order parameters mean value of P2 and mean value of P4 as well as the diffusion coefficient of the long molecular axis. It is shown that increasing unsaturation in the acyl chains of the PC lipids results in an increase in the rotational diffusion rates of the probes and a decrease in the order parameter mean value of P2. However, the value of mean value of P4 remains unchanged. The corresponding orientational distribution function of the probes is bimodal, with fractions lying preferentially parallel and perpendicular to the local vesicle surface. Surprisingly, the fraction of probe molecules lying with their long axes parallel to the bilayer surface increases with increasing unsaturation with a concomitant narrowing in the width of the distribution of the fraction lying perpendicular to it. As expected, cholesterol is found to increase the order parameters in all the systems and to suppress the tendency of the molecules to lie parallel to the bilayer surface. Furthermore, the rotational diffusion coefficients of the probes is found to increase in all the systems except for DLPC. Interestingly, the effects of unsaturation on the reorientational dynamics of TMA-DPH molecules in the vesicle systems are opposite to those found in the corresponding planar multibilayers (Deinum et al. 1988), whereas the same cholesterol effect is observed for the two systems. Nevertheless, the TMA-DPH molecules exhibit higher diffusion coefficients in the vesicle than in the planar multibilayer systems. In addition, a unimodal distribution of the probe molecules is found in the multibilayer systems. The differences between the two systems are ascribed to the differences in the radius of curvature and the hydration of the bilayers. Lastly we rationalize the bimodal distribution of the TMA-DPH molecules in the vesicles in terms of their observed partition between the lipid and aqueous phases.

Correlation of membrane order and dynamics derived from time-resolved fluorescence measurements with solute permeability

“…For TMA‐DPH, an increasing tendency of D ⊥ was apparent upon addition of chol or DMPC in concentrations of up to 20% to POPC bilayers. This is in agreement with the results of other groups who also observed an increase of D ⊥ when chol was added to POPC bilayers 31,38. At the highest chol concentration of 30%, however, a sharp decline of D ⊥ was found.…”

“…A single set of values for the adjustable parameters was obtained from this simultaneous fitting of $I_{{\rm VV}}^{{\rm Bkg}} (t)$ and $I_{{\rm VH}}^{{\rm Bkg}} (t)$ . The ratio of the two α‐values was fixed to α 1 = 3*α 2 31 to reduce correlation between the parameters. Varying this ratio within a wide range was found to have no effect on the quality of the fit or on the resulting values of the parameters describing the anisotropy decay.…”

Diphenylhexatriene membrane probes DPH and TMA-DPH: A comparative molecular dynamics simulation study

“…Additionally, the calculated limiting anisotropies are close to those measured in DPPC (~0.05 and 0.14 for DPH and TMA-DPH, respectively [9]) and DMPC (~0.06 and 0.14 for DPH and TMA-DPH, respectively [88]) vesicles both above their phase transition temperatures (at 45°C and 25°C, respectively). Turning our attention to the systems with cholesterol, our values are in reasonable accordance (though somewhat higher) with the experimental data of Mitchell and Litman [89] for DPH in POPC/30 mol% cholesterol (0.738 at 20°C, 0.674 at 30°C) and with those of van Langen et al [87] for TMA-DPH in POPC/25 wt.% cholesterol (0.67 at~20°C).…”

“…The estimated probe order parameters in the absence of cholesterol agree reasonably well with experimental values measured by Prendergast et al [9] at~300 K (0.33 and 0.59 for DPH and TMA-DPH, respectively), as well as with those obtained by Mitchell and Litman [13] for DPH (0.346 at 20°C, 0.262 at 30°C) and van Langen et al [87] for TMA-DPH (0.54 at~20°C), all in POPC bilayers. Our higher values for DPH probably reflect increased ordering induced by the larger probe concentration in our simulations (if we only considered the 2 DPH system in this calculation, S = 0.36 would be obtained, closer to the experimental values).…”

Glucosylceramide Contained in Koji Mold-Cultured Cereal Confers Membrane and Flavor Modification and Stress Tolerance to Saccharomyces cerevisiae during Coculture Fermentation

“…Indeed, sphingolipids interact with sterols through van der Waals interactions and form specific membrane regions called "rafts" (41). The physicochemical status of the membrane is also affected by the length of the fatty acids through the lateral packing of lipid molecules (42)(43)(44)(45). The length of the fatty acids in GlcCers from plants and fungi is C 16 to C 20 (21,22,30), whereas the length of those in the phosphodiester-linked complex sphingolipids of yeast is usually C 26 (46,47).…”