oxonol-vi and merocyanine-dye

Topics: Animals; Carbocyanines; Carotenoids; Energy Metabolism; In Vitro Techniques; Isoxazoles; Kinetics; Membrane Potentials; Models, Molecular; Molecular Probes; Pyrimidinones

Differential scanning calorimetry (DSC) has been employed to determine the effect of five commonly employed extrinsic potential-sensitive probes on phase transitions of multilamellar suspensions of L-alpha-dimyristoylphosphatidylcholine (DMPC). At mol% values of less than five, the effect of these probes on the excess heat capacity curve in the vicinity of the gel to liquid crystal phase transition can be described by an equation based on the formation of ideal solutions in both phases. Even at up to 4 mol%, these dyes only moderately reduce the enthalpy change associated with this transition, but cause a marked decrease in the size of the cooperative unit parameter. The excess heat capacity profile for diS-C3-(5) is represented by the ideal solution equation, even at 12 mol%, whereas the suspensions with the other probes present at this level have profiles covering large temperature ranges. Multiple peaks appear at the higher levels for the negatively charged oxonols V and VI, and merocyanine 540, a result consistent with the presence of well-defined microdomains or even phase separation. The enthalpy change associated with the transition near 15 degrees C involving packing in the headgroup region is decreased significantly, indicating that the probes probably affect the lipid headgroup conformation, even at low levels. The cyanine probe diS-C3-(5) causes the heat capacity profile of small unilamellar vesicles to be transformed very rapidly into one similar to that of the vortexed lipid preparations, presumably by a dye-mediated vesicle fusion process, enhanced by the surface location of this probe. All our results are consistent with diS-C3-(5) being located on the surface of the bilayer in both phases, but a penetration of the other probes into the hydrocarbon region, at least in the liquid crystal phase.

Topics: Algorithms; Calorimetry, Differential Scanning; Dimyristoylphosphatidylcholine; Isoxazoles; Mathematics; Molecular Probes; Pyrimidinones

The effect of a number of commonly employed potential-sensitive molecular probes on the 31P-NMR properties of dimyristoylphosphatidylcholine vesicles at two field strengths has been investigated in order to obtain information on the location and effect of these probes on the membrane bilayer. In comparison to the control dye-free vesicle spectrum, the probes diS-C3-(5) and diS-C4-(5), when added to a vesicle suspension, cause a substantial broadening of the 31P resonance with no detectable chemical shift within an uncertainty of +/- 0.05 ppm at 24 MHz. The spin-lattice and spin-spin relaxation times are also reduced when the cyanines are present by well over 20% relative to those of the control vesicle preparation. The addition of anionic probes, including several oxonol derivatives and merocyanine 540, causes no chemical shift, line broadening, or changes in the relaxation times. Possible explanations for the failure of the anionic probes to alter the vesicle 31P-NMR properties include charge repulsion between these dyes and the phosphate group that prevents the probes from penetrating the bilayer to a depth sufficient to alter the local motion of the phosphate moiety. The 31P resonance broadening and reduction in the relaxation times caused by the two cyanines is at least in part due to an increase in vesicle size as judged by electron microscopy measurements, although an inhibition of the local phosphate motion as well cannot be completely eliminated. The cyanine-mediated increase in vesicle size appears to be due to an irreversible vesicle-fusion process possibly initiated by the screening of surface charge by these probes. The implications of these observations in relation to functional energy-transducing preparations is discussed.

Topics: Benzothiazoles; Carbocyanines; Dimyristoylphosphatidylcholine; Indicators and Reagents; Isoxazoles; Kinetics; Lipid Bilayers; Magnetic Resonance Spectroscopy; Membrane Potentials; Microscopy, Electron; Oxazoles; Pyrimidinones; Quinolines