Phosphatidylcholines quenching

Solubilization of an active H,K-ATPase is also a prerequisite for reconstitution of the enzyme into liposomes. With these H,K-ATPase proteoliposomes it is then possible to study the transport characteristics of pure H,K-ATPase, without the interference of residual protein contamination that is usually present in native vesicular H,K-ATPase preparations. Rabon et al. [118] first reported the reconstitution of choleate or n-octylglucoside solubilized H,K-ATPase into phosphatidylcholine-cholesterol liposomes. The enzyme was reconstituted asymmetrically into the proteoliposomes with 70% of the pump molecules having the cytoplasmic side extravesicular. In the presence of intravesicular K, the proteoliposomes exhibited an Mg-ATP-dependent H transport, as monitored by acridine orange fluorescence quenching. Moreover, as seen with native H,K-ATPase vesicles, reconstituted H,K-... 

Cantrell et al. (2003) studied the quenching of 02 by several dietary carotenoids in dipalmitoyl phosphatidylcholine (DPPC) unilamellar liposomes. These workers used water soluble and lipid soluble 02 sensitizers so that a comparison of the efficiencies of quenching 02 generated within and outside the membrane model could be made. Perhaps surprisingly there was little difference in the efficiency of quenching in either situation. Typical results are presented in Table 14.3 (taken from Cantrell et al. (2003 and 2006)). 

Plots of t0/t for varying [Q]T are first otained for different concentrations of lipid. Then, form the slope and intercept of a plot of k pp against am, the value of the partition coefficient is obtained. This method has been applied to the partitioning of lindane into lipid bilayers.(102 103) An example is shown in Figure 5.4 for the quenching of DPH by 5-DOXYL-decane in dimyristoyl-phosphatidylcholine vesicles(104) the increase in the partition coefficient as the... 

Figure 5.4. EfTect of the phase transition on the partition coefficient of 5-DOXYL-decane calculated on the basis of its ability to quench the fluorescence of DPH in dimyristoyl-phosphatidylcholine vesicles. The fluorescence anisotropy of the DPH is also shown. (From Ref. 104, with permission.)...

M. Caffrey and G. W. Feigenson, Fluorescence quenching in model membranes. 3. Relationship between calcium adenosinetriphosphatase enzyme activity and the affinity of the protein for phosphatidylcholines with different acyl chain characteristics, Biochemistry 20, 1949-1961 (1981). 

P. L.-G. Chong and T. E. Thompson, Oxygen quenching of pyrene-lipid fluorescence in phosphatidylcholine vesicles, Biophys. J. 47, 613-621 (1985). 

The quenching mechanism of Vitamin E (21) toward hydroperoxides is depicted in equation 11 (Section II.A.2.d). The structure of products 38 obtained when quenching hydroperoxides from phosphatidylcholines (155) was elucidated by the usual MS and NMR techniques. ... 

Figure 3 shows a freeze-fracture microphotograph of a 50 50 binary mixture of (II) and (IV) quenched from a temperature ( 25°C) where roughly equal proportions of solid and fluid phases are expected to coexist. The banded region corresponds to the crystalline, monoclinic P solid solution phase and the nonbanded region to the fluid phase. For a recent crystallographic study of the P phase of phosphatidylcholines, see Ref. 22. For a freeze-fracture study of this phase, see Ref. 28. 

Because the dynamics of phospholipid membranes have been well characterized using AF probes [8-13], fluorescence results obtained with hydrated human SC were compared to aqueous suspensions of unilamellar distearoyl-phosphatidylcholine (DSPC) vesicles. DSPC was also used because its phase transition temperature (55°C) is close to that of SC lipids (65 C). The microenvironment inside DSPC and SC membranes was studied by measuring fluorescence lifetimes, and shifts in emission maxima were compared to excitation maxima (Stokes shifts), along with quenching of a series of AF probes by iodide. Stokes shifts (Av) [6] were calculated as ... 

Non-Forster fluorescence quenching of trans-etiochlorin by magnesium oc-taethylporphine in phosphatidylcholine vesicles gives evidence for a statistical pair energy trap. Energy transfer also occurs in the excited singlet manifold of chlorophyll. " The photophysics of bis(chlorophyll)-cyclophanes, models of photosynthetic reaction centres, have been explored for use in artificial photosynthesis.Picosecond time-resolved energy transfer in phycobilosomes have also been studied with a tunable laser. The effect of pH on photoreaction cycles of bacteriorhodopsin, " the fluorescence polarization spectra of cells, chromatophores, and chromatophore fractions of Rhodospirillum rubrum, and a brief review of the mechanism and application of artifical photosynthesis are all relevant to the subject of this Chapter. 

---