The protein-mediated phospholipid exchange between small unilamellar vesicles was investigated by fluorescence polarization measurements with diphenylhexatriene as optical probe. Thermotropic phase-transition measurements were taken after mixing two vesicle preparations of distinct and different phase-transition temperatures or having different states of charge. From the heights of each phase-transition step, we were able to follow the lipid-exchange process in the presence, as well as in the absence (natural exchange), of so-called transfer protein isolated from beef liver. A strong enhancement of the lipid transfer was observed at the corresponding lipid-phase-transition temperature, which is explained by the presence of fluctuating fluid and ordered domains co-existing at the lipid-phase-transition temperature. A unidirectional lipid transfer of the neutral component was observed between negatively charged phosphatidic acid and neutral phosphatidylcholine vesicles. Fluorescence polarization measurements showed the disappearance of the phosphatidylcholine phase transition, whereas the phosphatidic acid phase transition broadened and its phase transition temperature became lower.
In this paper, 4, 4’-Azobisphenol was synthesized with three methods which were high temperature reduction, Pb-reduction and diazotize-coupling, and diazotize-coupling was the best way. 4, 4’-Azobisphenol derivatives-1, 2- bis(4-(alloxy/hexyloxy)phenyl) diazene were synthesized through etherification. The structures of these compounds were characterized by the methods of 1H-NMR and FTIR. Phase-transition temperature was measured by DSC, and the phase behaviors were studied by the polarizing microscope. In those derivatives, only1, 2- bis(4-(hexyloxy)phenyl) diazene had mesomorphic phase and mosaic texture. Its mesomorphic phase temperature ranged from 89.3°C to101°C.
1H-NM R studies on DPPC vesicles labelled with the spin label (1,14) have been performed below (34 °C) and above (52 °C) the phase transition temperature. At both temperatures, the spin label, located at the apolar end of the CH2 chain, affects the whole structure of the lipids. Structural and functional investigations of membranes using spin labels have to consider always the effect described.
A low membrane lipid phase transition temperature is associated with a high cryotolerance of Lactobacillus delbrueckii subspecies bulgaricus CFL1