The preparation of polyene fatty acid membrane probes cis- and trans-parinaric acid and parinaroylphosphatidylcholines and their use in studies of several one- and two- component lipid systems are described. The fluorescence quantum yield of trans-parinaric acid in dipalmitoylphosphatidylcholine at 20 degrees C is approximately 0.3; the quantum yield in aqueous solution is negligibly small. Thermal-phase transitions in single-component phospholipid dispersions are monitored with absorption and fluorescence excitation peak position, fluorescence intensity, lifetime, and polarization. The transition temperatures observed are consistent with previous determinations. Shifts in the absorption peak position are related to the bilayer expansion as it undergoes the gel to liquid-crystalline transition, while fluorescence depolarization provides semiquantitative information concerning molecular motion of the probe in the bilayer. A long fluorescence lifetime component is observed for parinaric acid in the solid phase (up to 50 ns), and a short lifetime component is observed (ca. 5 ns) in the fluid phase of dipalmitoylphosphatidylcholine; both lifetime components are observed in the transition region. In most phospholipids, cis-parinaric acid detects the melting transition at about 1 degree C lower than trans-parinaric acid. Partitioning experiments involving mixed populations of phospholipid vesicles show that trans-parinaric acid preferentially associates with solid-phase lipids, while cis-parinaric acid shows a more equal distribution between solid and fluid lipids. The binding of cis-parinaric acid to dipalmitoylphosphatidylcholine at 25 degrees C is described as partitioning of parinaric acid between lipid vesicles and the aqueous phase with a partition coefficient of 5 X 10(5). Several rates are observed in the binding process which are interpreted as rapid outer monolayer uptake and a much slower process of interlamellar exchange. The phase diagram of the binary lipid mixture dipalmitoylphosphatidylcholine-dipalmitoylphosphatidylethanolamine has also been examined and found to be essentially identical to the one constructed using a nitroxide probe.

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We have studied the transport of newly synthesized cholesterol from the endo: plasmic reticulum to the plasma membrane in Chinese hamster ovary cells using a cell fractionation assay. We found that transport is dependent on metabolic energy, but that the maintenance of the high differential concentration of cholesterol in the plasma membrane is not an energy-requiring process. We have tested a variety of inhibitors for their effect on cholesterol transport and found that cytochalasin B, colchicine, monensin, cycloheximide, and NH4CI did not have any effect. The cholesterol transport process shows a sharp temperature dependence; it ceases at 15 °C, whereas cholesterol synthesis continues. When synthesis occurs at 15°C, the newly synthesized cholesterol accumulates in the endoplasmic reticulum and in a low density, lipid-rich vesicle fraction. These results suggest that cholesterol is transported via a vesicular system.

The function of the £ subunit of the Escherichia coli proton-translocating ATPase has been examined by using a mutant defective in the uncC gene. Strains with a defective uncC gene show a reduction in both growth yield and growth rate that is more severe than for other unc mutants; this deleterious effect is shown to be a result of the ATPase activity of the F1 complex which is missing the £ subunit. In addition, the £-deficient F1 is bound less tightly to the membrane. These data suggest that, in vivo, the £ subunit is capable of inhibiting the ATPase activity of F1 and also functions in the binding of F1 to Fo. The proton-translocating ATPase of Escherichia coli is a complex multimeric enzyme composed of two structural units, Fo and F1. Three subunits, a, b, and c, form the Fo