Subzero temperature study of the inner mitochondrial membrane and related phospholipid membrane systems with the fluorescent probe, trans-parinaric acid

Apolipoprotein A-I localization and dipalmitoylphosphatidylcholine dynamics in reconstituted high density lipoproteins

The structure and molecular dynamics of recombinant high density lipoproteins (rHDL) were studied by non-radiative energy transfer (NRET), fluorescence anisotropy and intensity measurements. The rHDL particles contained human plasma apolipoprotein (apo) A-I and dipalmitoylphosphatidylcholine (DPPC). Fluorescent cis- and trans-parinaric acids were used both as probes of molecular motion in the particle lipid phase and as acceptors in the Forster's energy transfer from apo A-I tryptophan residues to determine particle dimensions, apolipoprotein localization and lipid dynamics. The probes are sensitive to thermal wobbling (macromobility) and conformational deformations (micromobility) of phospholipid acyl chains. The experimental data fitted to various models of the particle structure are compatible with the following: (a) at T < Tt the particles appeared as lens-like discs with a radius of the lipid phase of 5 nm and a mean thickness of 4 nm, the value being more by 20% in the particle centre, the alpha-helices of about 1 nm thickness were located around the edge of the lipid core. Compared to liposomes, both macro- and micromobility of DPPC molecules in rHDL were more rapid due to a significant disorder of the boundary lipid molecules close to the apo A-I molecule. This disorder led to the increase of the specific surface area per one lipid molecule, S(o). The lipid phase can be divided into three regions: (i) zone I of the most tightly packed lipid (0-1.7 nm from the disc axis) with a S(o) value small as 0.5 nm2; (ii) intermediate zone II (from 1.7 to 4.0 nm); and (iii) boundary lipid zone III (4-5 nm) of significantly disordered lipid with a S(o) value large as 0.65 nm2. (b) at T> Tt the S(o) heterogeneity disappeared, the radius of the lipid phase did not increase significantly, not exceeding 5.2-5.4 nm, but protein-induced immobilization of lipid molecules which affected about half or more of the total lipid, became remarkable. The overall effect was the suppression of the transition amplitude in rHDL compared to liposomes. The structural inhomogeneity might underlie the function of the native plasma HDL as the key component of the transport and metabolism of plasma lipids.

Changes in chemical structure and function in Escherichia coli cell membranes caused by freeze-thawing. I. Change of lipid state in bilayer vesicles and in the original membrane fragments depending on rate of freezing

The effect of different rates of freezing on the character of lipids in unilamellar lipid bilayer vesicles and in the original membrane fragments of Escherichia coli B cells was investigated by measuring the temperature-dependent fluorescence polarization ratio changes of cis- and trans-parinaric acids. In lipid bilayer vesicles, both slow and rapid freezing brought about significant alterations in fluorescence polarization ratios in the specimens derived from both logarithmic and stationary-phase cells. In the original membrane fragments derived from logarithmic-phase cells, slow freezing gave rise to a similar alteration in fluorescence polarization ratio change, but no such alteration was found in the case of rapid freezing. Logarithmic-phase cells suffered from a membrane permeability change during slow freezing, which subsequently resulted in low cell viability. The cells suffered only slight impairment in membrane function during rapid freezing, and maintained higher viability. These results suggest that the primary site of damage due to freezing of the cells is the cellular membranes, and this destruction is due to a lipid state change in the membranes brought about by freezing.

Fluorescence polarization studies on Escherichia coli membrane stability and its relation to the resistance of the cell to freeze-thawing. II. Stabilization of the membranes by polyamines

The effects of polyamines, spermine, spermidine and putrescine on the stabilization of the membrane organization of Escherichia coli cells were studied using measurements of fluorescence polarization change of extrinsic fluorescence probes in membrane specimens as a function of temperature. The effects of the polyamines on the restoration of the cell viability after freeze-thawing were also investigated. In logarithmic-phase membrane specimens, polyamines depressed the polarization ratio increase below the transition temperatures in a dose-dependent manner. The physiologically relevant concentration of polyamines repressed the ratios to the same levels as are obtained with the stationary-phase specimens. In the stationary-phase specimens, no effect of polyamines on repression of the polarization increase was observed. A preliminary exposure of logarithmic-phase cells to polyamines protected the cells from the reduction of viability in freeze-thawing. However, a considerably high concentration and a certain length of preincubation time were required in order to an effect to be exerted. These results indicate that the intracellular polyamines could stabilize the membrane organization of logarithmic-phase cells to the same extent as in the stationary-phase cell membranes. It is conjectured that the membrane stability which is mediated by the polyamines results in cellular resistance to freeze-thawing, as it is attained by increasing the growth phase of the cells.

Fluorescence polarization studies on Escherichia coli membrane stability and its relation to the resistance of the cell to freeze-thawing. I. Membrane stability in cells of differing growth phase

Physical properties of Escherichia coli membrane lipids in logarithmic- and stationary-phase cells were studied by measuring the fluorescence polarization change of cis- and trans-parinaric acid as a function of temperature. In aqueous dispersions of phospholipids extracted from cytoplasmic and outer membranes of cells of differing growth phase, a similar polarization increase was observed over the range from physiological temperature to below 0 degrees C, and nearly the same transition ratios were obtained in all samples. The cytoplasmic membrane of both of the growth-phase cells showed a higher polarization ratio above the transition temperatures, compared to that in the aqueous dispersion of phospholipids. The polarization ratios below the transition temperatures of these specimens were lower than the value obtained with the lipids, especially in the stationary-phase specimens. The outer membrane specimens showed a similar polarization change but the transition temperature ranges were considerably higher both in the logarithmic- and the stationary-phase specimens, compared to those in the cytoplasmic membrane specimens. Freeze-thawing of logarithmic-phase cells showed the emergence of activity of certain enzymes which are known to be located in the membranes. The stationary-phase cells did not suffer from any such deleterious effect and maintained a high level of cell viability in a similar treatment. These results indicate that in the stationary-phase cell membranes lipids are in a highly ordered state, and the lipid state causes a membrane stability which results in the high resistance of the cell to freeze-thawing.

Static and time-resolved fluorescence studies of fluorescent phosphatidylcholine bound to the phosphatidylcholine transfer protein of bovine liver

Phosphatidylcholine analogues containing a cis- parinaroyl chain at the sn-1, sn-2, or both sn-1 and sn-2 positions (1-PnA-PC, 2-PnA-PC, and diPnA -PC, respectively) have been used to investigate the lipid binding site of the phosphatidylcholine transfer protein (PC-TP) from bovine liver by fluorometric techniques. Binding of these fluorescent lipids to the protein was registered by measuring the enhancement of parinaroyl fluorescence and the quenching of the tryptophanyl fluorescence. The fluorescence intensity of 1-PnA-, 2-PnA- and diPnA -PC bound to PC-TP was proportional to the chromophore content. The energy-transfer efficiency between the tryptophan residues and the bound chromophores was approximately 40% for 1-PnA- and 2-PnA-PC and 60% for diPnA -PC. Quenching of the tryptophanyl fluorescence was, in part, accounted for by a decrease of the fluorescence lifetimes. The orientation of the 1 and 2 fatty acyl chains of the PnA-PC analogues on the transfer protein was analyzed by time-resolved fluorescence anisotropy measurements. The fluorescence anisotropy decayed according to a single exponential function yielding a rotational correlation time of 26 ns for 1-PnA-PC, 11 ns for 2-PnA-PC, and 15 ns for diPnA -PC. These correlation times indicate that both fatty acyl chains are immobilized at different positions on the protein. From the difference in correlation time we propose that the shape of the phosphatidylcholine transfer protein is ellipsoidal (axial ratio congruent to 2.5) with the 1 fatty acyl chain oriented parallel to the long symmetry axis and having an angle of 60-90 degrees with the 2 fatty acyl chain.

Escherichia coli B membrane stability related to cell growth phase. Measurement of temperature dependent physical state change of the membrane over a wide range

Escherichia coli B cytoplasmic and outer membrane from cells in different growth phases showed different chemical compositions. In freezing, logarithmic phase cells showed a marked permeability increase in the outer as well as the cytoplasmic membrane. Whereas, in the stationary phase cells no such change in membrane permeability was observed. Cooling of phospholipids and lipopolysaccharides with trans-parinaric acid showed a distinct fluorescence increase from room temperature to far below 0 degrees C. In the outer membrane the fluorescence similar to that of lipopolysaccharides was shown. The outer membranes of cells in different growth phases showed similar temperature-dependent fluorescence changes. The cytoplasmic membrane inhibited a temperature-dependent fluorescence similar to that of the phospholipids. The onset temperature of the increase in fluorescence differed with the cells at different growth phases. The presence of EDTA and MgCl2 modified the fluorescence changes in the membranes from cells in logarithmic phase. Whereas, in the membranes from cells in stationary phase no such effect was observed. These results suggest that the organizational stability of the membranes from cells in stationary phase is a fundamental basis of the membrane's resistance to the freezing damage.

Studies on fluorescence polarization of 1-acyl-2-cis- or trans-parinaroyl sn-3-glycerophosphorylcholines in model systems and microsomal membranes

Fluorescent lecithin probes containing cis- or trans-parinaric acid (PnA) at the 2-position cis-parinaroylphosphatidylcholine (cis-PnPC) and trans-parinaroyl phosphatidylcholine (trans-PnPC)) showed similar behavior to that of the free cis- or trans-parinaric acids (cis-PnA or trans-PnA) in bilayer vesicles of synthetic saturated lecithins. Transition temperatures detected by cis-PnPC were about 1 degree C than those observed with trans-PnPC. In mixed lecithin vesicles, the trans-PnPC probe monitored a higher temperature melting component than did the cis-probe. Both probes were readily incorporated into microsomal membranes and into sonicated vesicles prepared from the microsomal phospholipids. With either cis- or trans-PnPC no change in polarization ratio was observed for microsomal membranes between 40 degrees C and 0 degrees C but this ratio increased with decreasing temperature between 0 degrees C and -5 degrees C. However, vesicles of extracted phospholipids showed a continuous increase in polarization ratio with decreasing temperature between 20 degrees C and -15 degrees C with trans-PnPC and between 5 degrees C and -15 degrees C with cis-PnPC. These results suggest that the two lecithin probes monitor different environments in the membranes and phospholipid vesicles prepared from them.