A theory of fluorescence depolarization in membranes

Orientational distribution of DPH in lipid membranes: a comparison of molecular dynamics calculations and experimental time-resolved anisotropy experiments

The behavior of the fluorescent probe diphenylhexatriene (DPH) in different lipid phases is investigated. The rotational autocorrelation functions are calculated in order to model the time-resolved fluorescence anisotropy decay. The role of the order parameters is discussed.

Orientation distribution functions based upon both (P1), (P3) order parameters and upon the four (P1) up to (P4) values: application to an electrically poled nonlinear optical azopolymer film

The most probable orientational distribution functions of rod-like polar molecules contained in a noncentrosymmetric uniaxial system are established using the first-rank and third-rank Legendre polynomials, (P1(cos theta)) and (P3(cos theta)) order parameters, and the maximum entropy method. Emphasis is put on the different domains of existence in the ((P1), (P3)) plane for the various shapes of the distributions: it is thus shown that, for any positive (P1(cos theta)) value and for decreasing (P3(cos theta)) values, the distribution function may exhibit either a distorted oblate form with an intense maximum at 0 degrees, or a three-leaved rose curve with maxima at 60 degrees, 180 degrees, and 300 degrees, and finally another markedly oblate shape with a strong maximum at 180 degrees. As an illustrative example, we have considered the azobenzene molecular orientations in an electrically poled p(DR1M) homopolymer thin film after a thermal process and several relaxation periods. We have made use not only of the (P1) and (P3) parameters determined from polarized second-harmonic generation (SHG) measurements, but also of the (P2) values extracted from UV-visible spectra and of the (P4) values adjusted according to the information entropy theory. In such a thin film with very large nonlinear properties (d33 coefficients were varying from 437.0 to 117.0 pm/V at 1064 nm) it is evidenced that a strong polar order is maintained even after a long relaxation period of 42 days. So, the distribution functions demonstrate that the poling treatment was quite efficient and they emphasize the importance in the determination of both couples of odd and even order parameters in such uniaxially oriented optical elements.

Changes of mitochondrial properties in maize seedlings associated with selection for germination at low temperature. Fatty acid composition, cytochrome c oxidase, and adenine nucleotide translocase activities

Mitochondria are affected by low temperature during seedling establishment in maize (Zea mays L.). We evaluated the associated changes in the mitochondrial properties of populations selected for high (C4-H) and low (C4-L) germination levels at 9.5 degreesC. When seedlings of the two populations were grown at 14 degreesC (near the lower growth limit), the mitochondrial inner membranes of C4-H showed a higher percentage of 18-carbon unsaturated fatty acids, a higher fluidity, and a higher activity of cytochrome c oxidase. We found a positive relationship between these properties and the activity of a mitochondrial peroxidase, allowing C4-H to reduce lipid peroxidation relative to C4-L. The specific activity of reconstituted ATP/ADP translocase was positively associated with this peroxidase activity, suggesting that translocase activity is also affected by chilling. The level of oxidative stress and defense mechanisms are differently expressed in tolerant and susceptible populations when seedlings are grown at a temperature near the lower growth limit. Thus, the interaction between membrane lipids and cytochrome c oxidase seems to play a key role in maize chilling tolerance. Furthermore, the divergent-recurrent selection procedure apparently affects the allelic frequencies of genes controlling such an interaction.

Mitochondrial respiratory chain features after gamma-irradiation

Radiation provokes damage to DNA but also to membrane and protein structure. Radiolysis is a tool used very often in the study of free radical biological effects and of scavenger molecules effectiveness. Nitroimidazoles have been demonstrated to enhance the radiation effects on biological structures. The studies we have performed on isolated mitochondria irradiated, with and without nitroimidazoles, at a radiation dose equal to LD90, indicate that this treatment is not able to affect the structural and functional features investigated (ubiquinone-10, fatty acids, respiratory cytochrome levels or membrane fluidity and respiratory enzymatic activities), suggesting that an involvement of such externally produced radicals on membrane damage is unlikely. Moreover it was ascertained that the mitochondrial redox activities do not take part into the intracellular nitroimidazole reduction.

Fluorescence decay of DPH in lipid membranes: influence of the external refractive index

The radiative decay rate of a fluorescent probe in an optically thin layer is known to depend on the orientation of the probe and on the refractive indices inside and outside the layer (W. Lukosz, Phys. Rev. B 22 (1980) 3030). Fluorescent probes in phospholipid bilayer membranes approximate such a system. The natural lifetime is expected to vary with the refractive index of the medium surrounding the bilayer. The lifetime variation with the refractive index depends on the orientation of the fluorescent probe. This can be used to retrieve the second-rank orientational order parameter, <P2>. The fluorescence decay of all-trans 1,6-diphenyl-1,3,5-hexatriene in L-alpha-dipalmitoyl-phosphatidylcholine large unilamellar vesicles (LUVs) was measured at a temperature well below that of the phase transition. The refractive index of the medium was varied by addition of glycerol or sucrose. The observed change of decay time with the refractive index followed the theoretical prediction. The value of the order parameter, <P2>, recovered is significantly lower than that obtained from fluorescence polarization data. Possible reasons for this disagreement are discussed.

Use of fluorescent probes to monitor molecular order and motions within liposome bilayers

This article reviews the use of fluorescent probes to monitor the order and dynamics within the acyl chain region of liposome lipid bilayers. Fluorescence anisotropy is first defined and the theoretical framework that allows interpretation of steady-state or dynamic measurements in terms of molecular details is reviewed. The general advantages and/or limitations of fluorescent versus other methods of monitoring membrane order and dynamics are discussed. The properties of two classes of fluorescence probes are then described. The linear probes 1,6-diphenyl-1,3,5-hexatriene (DPH) and parinaric acid (PA) and their derivatives are seen as particularly useful when quantitative interpretation of observations in terms of details of bilayer dynamics and order are critical. Of these, DPH is the more widely and easily used, although parinaric acid has advantages for certain applications. The non-linear probes considered include the anthroyloxyl fatty acids and the recently introduced fluorenyl fatty acid probes. While the geometry and electronic configurations of these probes do not allow for detailed molecular interpretations, these probes can provide unique qualitative information about the state of the lipid bilayer at various positions along the acyl chains.

Gamma-linolenic acid dietary supplementation can reverse the aging influence on rat liver microsome delta 6-desaturase activity

We have recently demonstrated that in rats the process of delta 6-desaturation of linoleic and alpha-linolenic acids slows with aging. One method of counteracting the effect of slowed desaturation of linoleic acid would be to provide the 6-desaturated metabolite, gamma-linolenic acid (18:3(n-6) GLA) directly. We have here investigated the 6-desaturation of both linoleic and alpha-linolenic acids in liver microsomes of young and old rats given GLA in the form of evening primrose oil (EPO) (B diet) in comparison to animals given soy bean oil alone (A diet), monitoring also the fatty acid composition of liver microsomes and relating this to the microviscosity of the membranes. In young rats the different experimental diets did not produce any difference in delta 6-desaturase (D6D) activity on either substrate suggesting that, when D6D activity is at or near its peak, the variations in diet tested are unable to influence it. In the old animals the rate of 6-desaturation of linoleic and particularly of alpha-linolenic acid was significantly greater in the B diet fed animals than in the A diet fed. The effects of the diets on the fatty acid composition of liver microsomes were consistent with the findings with regard to 6-desaturation. Administration of GLA partially corrected the abnormalities of n-6 essential fatty acid (EFA) metabolism by raising the concentration of 20:4(n-6) and other 6-desaturated EFAs. Furthermore, the GLA rich diet also increased the levels of dihomo-gamma-linolenic acid and of 6-desaturated n-3 EFAs in the liver microsomes. The microviscosity of microsomal membranes as indicated by DPH polarization was correlated with the unsaturation index of the same membranes. There was a very strong correlation between the two. In both young and old rats the B diet reduced the microviscosity and increased the unsaturation index. However, the effect was much greater in the old animals.

Time-resolved fluorescence spectroscopy of NADPH-cytochrome P-450 reductase: demonstration of energy transfer between the two prosthetic groups

Fluorescence as well as fluorescence anisotropy decay parameters have been obtained from NADPH-cytochrome P-450 reductase by time-resolved fluorescence spectroscopy. The two flavins in the enzyme, FMN and FAD, are slightly fluorescent and exhibit heterogeneous fluorescence lifetimes, as observed with other flavoproteins. The time-dependent anisotropy is also multiexponential and is wavelength-dependent. The anisotropy decay is biexponential with two correlation times when the enzyme is excited at the red edge of the first absorption band (514 nm). When the enzyme is excited in the light absorption maximum (458 nm), an additional shorter correlation time is found, which contains information about the rate of energy transfer between the two flavins present in the enzyme. FMN-depleted NADPH-cytochrome P-450 reductase shows also only two correlation times, as does the enzyme in the "air-stable" semiquinone state when excited at 458 nm. Wavelength-dependent steady-state anisotropy measurements of native and FMN-depleted protein show that the former exhibits lower values than the latter in the region of the first absorption band, but when the red edge of the absorption band is reached, the anisotropy becomes equal in both preparations. A similar situation is encountered in model compounds, monomeric and dimeric flavins, immobilized in poly(methyl methacrylate). Both in the models and in the flavoprotein this can be attributed to failure of energy transfer at the red edge of the absorption band. From the results we were able to derive both geometric parameters and dynamic properties of both flavins in the NADPH-cytochrome P-450 reductase.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a hyperlipidic diet on lipid composition, fluidity, and (Na+-K+)ATPase activity of rat erythrocyte membranes

Feeding rats a hyperlipidic diet in which animals were offered daily a variety of high-energy food resulted in a significant increase of serum free fatty acids and a decrease of phospholipids with respect to controls. On the contrary, there were no significant differences in erythrocyte membrane total lipid composition between the two groups. Erythrocyte membranes showed a significant decrease in saturated fatty acid content and a significant increase in (n-6) polyunsaturated fatty acid content; (n-3) polyunsaturated fatty acids significantly decreased. Membrane fluidity, investigated by fluorescence polarization of diphenylhexatriene, significantly increased in the erythrocyte membranes of the experimental group. These results seem compatible with the decreased saturated/unsaturated fatty acid ratio. A significant decrease of (Na+-K+)ATPase activity occurred in erythrocyte membranes of the experimental group rats with respect to the controls.

Is ubiquinone diffusion rate-limiting for electron transfer?

The different possible dispositions of the electron transfer components in electron transfer chains are discussed: random distribution of complexes and ubiquinone with diffusion-controlled collisions of ubiquinone with the complexes, random distribution as above, but with ubiquinone diffusion not rate-limiting, diffusion and collision of protein complexes carrying bound ubiquinone, and solid-state assembly. Discrimination among these possibilities requires knowledge of the mobility of the electron transfer chain components. The collisional frequency of ubiquinone-10 with the fluorescent probe 12-(9-anthroyl)stearate, investigated by fluorescence quenching, is 2.3 X 10(9) M-1 sec-1 corresponding to a diffusion coefficient in the range of 10(-6) cm2/sec (Fato, R., Battino, M., Degli Esposti, M., Parenti Castelli, G., and Lenaz, G., Biochemistry, 25, 3378-3390, 1986); the long-range diffusion of a short-chain polar Q derivative measured by fluorescence photobleaching recovery (FRAP) (Gupte, S., Wu, E. S., Höchli, L., Höchli, M., Jacobson, K., Sowers, A. E., and Hackenbrock, C. R., Proc. Natl. Acad. Sci. USA 81, 2606-2610, 1984) is 3 X 10(-9) cm2/sec. The discrepancy between these results is carefully scrutinized, and is mainly ascribed to the differences in diffusion ranges measured by the two techniques; it is proposed that short-range diffusion, measured by fluorescence quenching, is more meaningful for electron transfer than long-range diffusion measured by FRAP, or microcollisions, which are not sensed by either method. Calculation of the distances traveled by random walk of ubiquinone in the membrane allows a large excess of collisions per turnover of the respiratory chain. Moreover, the second-order rate constants of NADH-ubiquinone reductase and ubiquinol-cytochrome c reductase are at least three orders of magnitude lower than the second-order collisional constant calculated from the diffusion of ubiquinone. The activation energies of either the above activities or integrated electron transfer (NADH-cytochrome c reductase) are well above that for diffusion (found to be ca. 1 kcal/mol). Cholesterol incorporation in liposomes, increasing bilayer viscosity, lowers the diffusion coefficients of ubiquinone but not ubiquinol-cytochrome c reductase or succinate-cytochrome c reductase activities. The decrease of activity by ubiquinone dilution in the membrane is explained by its concentration falling below the Km of the partner enzymes. It is calculated that ubiquinone diffusion is not rate-limiting, favoring a random model of the respiratory chain organization.(ABSTRACT TRUNCATED AT 400 WORDS)

Anisotropy decay associated fluorescence spectra and analysis of rotational heterogeneity. 1. Theory and applications

Individual fluorescence spectra for species in a heterogeneous system can be determined by using differences between the rotational correlation times of those components. Each spectrum derived is associated with a particular fluorescence anisotropy decay function; hence, they are anisotropy decay associated spectra (ADAS). We have previously shown [Knutson, J. R., Walbridge, D. G., & Brand, L. (1982) Biochemistry 21, 4671-4679] that a system containing different decay functions for total intensity can be resolved into constituent decay-associated spectra. ADAS extends the technique into the realm of fluorescence polarization, making use of the often disparate Brownian rotations found in heterogeneous biochemical systems. In this paper, we present the basic theory for ADAS in various heterogeneous systems and then present an example of ADAS resolving a binary mixture of macromolecules into "fast-rotor" (smaller or more mobile) and "slow-rotor" (larger or less mobile) components. They correctly superimpose spectra taken for the unmixed components. In the companion paper [Davenport, L., Knutson, J. R., & Brand, L. (1986) Biochemistry (following paper in this issue)], a specific application to a problem of importance of lipid biochemistry--e.g., the origin of the membrane probe order parameter in lipid bilayers--is presented, demonstrating the role rotational heterogeneity may play in biochemical fluorescence.

Membrane NMR: a dynamic research area

Recent NMR relaxation studies of lipid bilayers and biomembranes are explained and briefly discussed. The results of both 2H and 13C NMR investigations suggest that, in addition to rapid local fluctuations of the hydrocarbon chains, slower, more collective motions of the bilayer exist. When the influence of the latter is recognized and properly accounted for, the contribution from local motions can be used to estimate a value for the microviscosity of the bilayer which corresponds to that of a simple n-paraffinic liquid. In general, the dynamic behavior of lipid bilayers as studied by NMR appears quite similar to that of simpler liquid crystals.

Angle resolved fluorescence depolarisation of 1,6-diphenyl-1,3,5 hexatriene (DPH) in unsaturated digalactosyl diacylglycerol (DGDG) lipid bilayers

The orientational ordering and dynamics of DPH molecules embedded in macroscopically ordered bilayers of the unsaturated galactolipid digalactosyl diacylglycerol (DGDG) were studied by angle-resolved fluorescence depolarisation at room temperature. The depolarisation ratios exhibited a weaker angular dependence than those observed for DPH incorporated in multi-bilayers of saturated lecithins above their phase transition. The results reflect the differences in the modes of reorientational motion of the DPH molecules in these systems while a similar orientational order is found. It is suggested that DPH molecules in bilayers of DGDG cannot be considered to possess an effective cylindrical symmetry in contrast to DPH in bilayers of saturated lecithins.

Lipid composition, physical state, and lipid peroxidation of tumor membranes

Studies were carried out on microsomes isolated from the highly differentiated (slow-growing) Morris hepatoma 9618A, on microsomes and plasma membranes from the poorly differentiated (fast-growing) Morris hepatoma 3924A, and rat liver used as control. The lipid composition (phospholipid and cholesterol content, degree of fatty acid unsaturation) and peroxidation of such membranes has been correlated with the order and fluidity of the membrane bilayer. The results indicate that substrate availability is the rate-limiting step in microsomal and plasma membrane lipid peroxidation of hepatoma 3924A. From diphenylhexatriene fluorescence depolarization measurements it appears that the changes in lipid composition cause an increase in the order of the lipid bilayer on going from the control to hepatoma 9618A and 3924A microsomes, while fluidity is virtually unchanged. Conversely, for similar chemical changes, in plasma membranes from hepatoma 3924A the order is nearly the same and there is a decrease in fluidity. The changes in the above parameters of tumor membranes might be partly related to the loss of protective enzymes against oxygen radicals. This is supported by the observation that inhibition of liver superoxide dismutase and glutathione reductase, by treatment of rats with diethyldithiocarbamate and chloroethyl nitrosourea, respectively, renders the microsomal membranes more resistant to lipid peroxidation in vitro.

Lipid peroxidation and fluidity of plasma membranes from rat liver and Morris hepatoma 3924A

Plasma membranes isolated from the fast-growing, maximal-deviation, Morris hepatoma 3924A exhibit remarkable changes in lipid composition, lipid peroxidation and to some extent in the physical state with respect to rat liver plasmalemmas. A correlation appears to exist between the lower phospholipid: protein ratio, higher cholesterol: phospholipid ratio, lower rate of lipid peroxidation and decrease in fluidity in tumor plasma membranes.