Incorporation of plastoquinone and ubiquinone into liposome membranes studied by HPLC analysis. The effect of side chain length and redox state of quinone

The efficiency of incorporation of plastoquinones and ubiquinones into phospholipid liposomes has been studied. The representatives of short (PQ1 and UQ1) middle (PQ4 and UQ4) and long (PQ9, UQ9 and UQ10) prenylquinones have been used to investigate the effect of quinone side chain length. The properties of hydroquinones have been also thoroughly examined in relation to the quinone forms. The extraction procedure was modified and further developed which enables removing of nonincorporated quinone by pentane washing and then determination of quinone content inside the lipid bilayer. The quantitatively evaluation of the amount of prenylquinone was assayed by means of HPLC analysis which offers much greater sensitivity and could be easily applied in case of hydroquinones. It has been found that PQ1 and UQ1 as well as their reduced forms were present mainly (about 80%) in the aqueous phase, when attempting to introduce them into phospholipid bilayer. In case of quinones having four and more isoprenyl units in side chain, a high level of quinone incorporation, ranging about 95%, was observed. The results pointed out that when comparing the effects of different exogenous quinones on membrane related processes, one has to consider the effectiveness of their incorporation within lipid bilayer.

Effect of monogalactosyldiacylglycerol and other thylakoid lipids on violaxanthin de-epoxidation in liposomes

In this study we present evidence that one of two reactions of the xanthophyll cycle, violaxanthin de-epoxidation, may occur in unilamellar egg phosphatidylcholine vesicles supplemented with monogalactosyldiacylglycerol (MGDG). Activity of violaxanthin de-epoxidase (VDE) in this system was found to be strongly dependent on the content of MGDG in the membrane; however, only to a level of 30 mol%. Above this concentration the rate of violaxanthin de-epoxidation decreased. The effect of individual thylakoid lipids on VDE-independent violaxanthin transformation was also investigated and unspecific effects of phosphatidylglycerol and sulphoquinovosyldiacyglycerol, probably related to the acidic character of these lipids, were found. The presented results suggest that violaxanthin de-epoxidation most probably takes place inside MGDG-rich domains of the thylakoid membrane. The described activity of the violaxanthin de-epoxidation reaction in liposomes opens new possibilities in the investigation of the xanthophyll cycle and may contribute to a better understanding of this process.

A mathematical model describing kinetics of conversion of violaxanthin to zeaxanthin via intermediate antheraxanthin by the xanthophyll cycle enzyme violaxanthin de-epoxidase

The xanthophyll cycle is one of the mechanisms protecting the photosynthetic apparatus against the light energy excess. Its action is still not well understood on the molecular level. Our model makes it possible to follow independently the kinetics of the two de-epoxidation steps occurring in the xanthophyll cycle: the conversion of violaxanthin into antheraxanthin and the conversion of antheraxanthin into zeaxanthin. Using a simple form of the transition rates of these two conversions, we model the time evolution of the concentration pattern of violaxanthin, antheraxanthin and zeaxanthin during the de-epoxidation process. The model has been applied to describe the reactions of de-epoxidation in a system of liposome membranes composed of phosphatidylcholine and monogalactosyldiacylglycerol. Results obtained within the model fit very well with the experimental data. Values of the transition probabilities of the violaxanthin conversion into antheraxanthin and the antheraxanthin conversion into zeaxanthin calculated by means of the model indicate that the first stage of the de-epoxidation process is much slower than the second one.

Cyclic Electron Flow Around Photosystem II as Examined by Photosynthetic Oxygen Evolution Induced by Short Light Flashes

Photosynthetic oxygen evolution from photosystem II particles was analyzed as consequence of a train of short (5 μs) flashes of different light quality and different intensities to study cyclic electron flow around photosystem II. Damped oscillations of the amplitudes of O2-evolution corresponding to a flash sequence were fitted numerically and analyzed in terms of a nonhomogeneous distribution of misses, represented by the probability parameter αi. Application of red light, known to promote cyclic electron flow around photosystem II (Gruszecki et al., 1995) results in a considerable increase of all αi, indicating that at the molecular level the misses may be interpreted as resulting from a competition for the reduction of oxidized P680 between cyclic electron flow and the electron flow coming from the water splitting enzyme. In accordance with previous findings, application of light flashes of the spectrum covering the absorption region of carotenoids resulted in an inhibition of cyclic electron flow and a pronounced decrease of the level of the miss parameter. Possible molecular mechanisms for the activity control of this cyclic electron transport around photosystem II by carotenoids are discussed.

Action of an antiserum to alpha-tocoquinone on photosystem II-particle preparations of Nicotiana tabacum

An antiserum to alpha-tocoquinone was prepared by immunization of rabbits. Immunization was obtained by injection of a conjugate consisting of the hapten alpha-tocoquinone attached to methylated ovalbumin into the rabbit. The antiserum recognizes the 3,4-dimethyl-p-benzoquinone group of the molecule as well as part of the immediate vicinity to the side chain. This is concluded from the fact that the antibody has some affinity also to plastoquinone. No reaction of the antibody is observed with alpha-tocopherol hydroquinone or alpha-tocopherol. Reaction of the antiserum to alpha-tocoquinone with photosystem II-particle preparations from tobacco affects the functionality of the preparation. Chlorophyll(a)-fluorescence emission is quenched without an alteration of the emission spectrum. Concomitant with this fluorescence quenching, the lifetime of two fluorescence components namely that of a fast and a slower component are shortened. By analogy with the literature the fast component is associated with chlorophyll(a) of the reaction center core and that of the slow component with the antenna system in which the lifetime parameter is shortened by the antibody from 3.42 ns to 1.795 ns. The action on the fast component is less and leads to a shortening of the lifetime parameter from 0.373 ns to only 0.249 ns. The effect is interpreted in terms of an enhancement of linear photosynthetic electron transport possibly due to an inhibition of the cyclic electron transport around PS II. discovered by Gruszecki et al. (1995), Z. Naturforsch. 50c, 61-68.

Influence of the redox state of ubiquinones and plastoquinones on the order of lipid bilayers studied by fluorescence anisotropy of diphenylhexatriene and trimethylammonium diphenylhexatriene

The measurements of diphenylhexatriene (DPH) and trimethylammonium diphenylhexatriene (TMA-DPH) fluorescence anisotropy in egg yolk lecithin (EYL) and of DPH anisotropy in dipalmitoylphosphatidylcholine (DPPC) liposomes containing different concentrations of oxidized and reduced ubiquinone (UQ) and plastoquinone (PQ) homologues have been performed. All the oxidized UQ homologues strongly induced ordering of EYL membrane structure, whereas in DPPC liposomes, above the phase transition temperature, the most pronounced effect showed UQ-4. PQ-2 and PQ-9 were less effective than the corresponding ubiquinones in this respect. The reduced forms of UQ and PQ homologues increased the order of membrane lipids to a smaller extent than the corresponding quinones both in the interior of the membrane and closer to its surface. Nevertheless, the investigated prenylquinols showed stronger increase in the membrane order than alpha-tocopherol or alpha-tocopherol acetate, which could be connected with binding of prenylquinol head groups to phospholipid molecules by hydrogen bonds. The strong ordering influence of ubiquinones on the membrane structure was attributed to methoxyl groups of the UQ quinone rings.

Changes in physical properties of vacuolar membrane during transformation of protein bodies into vacuoles in germinating pumpkin seeds

Changes in membrane molecular dynamics associated with the transformation of protein body membranes into vacuolar membranes during pumpkin seed germination, were monitored by EPR-spin probe technique. Using highly purified membrane preparations as well as 5-SASL and 16-SASL spin labels, parameters like general membrane lipid fluidity, order parameter, semicone angle, rotational correlation times tau 2B and tau 2C, ratio of immobilized to mobile lipids were determined and the activation energy for rotational diffusion of 16-SASL was calculated. Analysis of these parameters at different temperatures indicated a more rigid nature of protein body membrane comparing to vacuolar membrane, as a result of a more restricted motional freedom of lipids. These differences are discussed in terms of protein composition and various functional specialization of both types of membranes.

Mixed valence state in ironporphyrin aggregates

In biological systems, metalloporphyrins play a central role in energy and electron transfer process. Our aim is to understand the influence of ligands and iron coordination of ironporphyrin on the electron transfer. The lyophilized ironporphyrin, enriched in 57Fe up to 90% has been studied by Mössbauer spectroscopy between 2.8 and 313 K. Above room temperature the bounded diffusion of the ferric iron was observed. Below 293 K a part of iron appears in mixed Fe+3<==>Fe+2 valence state with 10 meV activation energy for the electron trapping. Below 4 K a part of iron shows magnetic ordering with a broad distribution of the hyperfine field. The results are discussed in terms of metalloporphyrin aggregation process.

Europium- and Dysprosium-Ions as Probes for the Study of Calcium Binding Sites in Photosystem II

Trivalent lanthanide cations are suitable probes for Ca2+-binding sites in photosystem II (PS II). PS II membranes prepared from Nicoticinci tabacum, intact and depleted of the extrinsic polypeptides were exposed to lanthanide ions (Dy3+ and Eu3+). Small concentrations of dysprosium and europium ions enhance oxygen evolution under short saturating flashes. Higher concentrations of the rare earth cations cause the release of the three extrinsic peptides (17, 23 and 33 kDa) and reduce O2 yield. The reactivation of the PS II membranes, thus depleted of the 33 kDa subunit, by Ca2+ ions is not possible. Comparing Eu3+ with Dy3+ in this effect shows that Eu3+ is more effective than Dy3+, because a lower Eu3+-concentration in comparison to that of Dy3+ inactivates O2-evolution. The differences between europium and dysprosium can be explained by their different ionic radius. Our results suggest the existence of two Ca-binding regions: one with a low affinity for calcium would be located on the contact surface of the 23 and 33 kDa proteins and the second one with a high affinity, should be located close to the Mn-cluster and to tyrosine-161 (Z ). The more tightly-bound calcium would be responsible for the activity of the PS II system.

Blue Light-Enhanced Photosynthetic Oxygen Evolution from Liposome-Bound Photosystem II Particles; Possible Role of the Xanthophyll Cycle in the Regulation of Cyclic Electron Flow Around Photosystem II?

Light-driven electron transport in liposome-bound photosystem II (PS-II) particles be­tween water and ferricyanide was monitored by bare platinum electrode oxymetry. The modi­fication of the experimental system with the exogenous quinones α-tocopherol quinone ( α-TQ) or plastoquinone (PQ) resulted in a pronounced effect on photosynthetic oxygen evolution. The presence of α-tocopherolquinone ( α-TQ) in PS-II samples decreased the rate of red light-induced oxygen evolution but increased the rate of green light-induced oxygen evolution. Blue light applied to the assay system in which oxygen evolution was saturated by red light resulted in a further increase of the oxygen signal. These findings are interpreted in terms of a cyclic electron transport around PS-II, regulated by an excitation state of β-carotene in the reaction centre of PS-II. A mechanism is postulated according to which energetic coupling of β-carotene in the reaction centre of PS-II and that of other antenna carotenoid pigments is regulated by the portion of the xanthophyll violaxanthin, which is under control of the xanthophyll cycle.

Antioxidant properties of plastoquinol and other biological prenylquinols in liposomes and solution

Oxidation of biological prenylquinols, like plastoquinol-9 (PQH2-9), ubiquinol-10 (UQH2-10), reduced vitamins K1 (VK1H2) and K2 (VK2H2), alpha-tocopherol quinol (alpha-TQH2) and alpha-tocopherol (alpha-T) was followed by their fluorescence during sonication of egg yolk lecithin/prenylquinol liposomes. The order of magnitude of oxidation of the prenylquinols by free radicals generated during sonication was UQH2-10 > VK2H2 > VK1H2 > alpha-TQH2 > PQH2-9 > alpha-T. It was shown that egg yolk lecithin undergoes degradation even when sonicated briefly under atmosphere of nitrogen and at 0 degree C. A kinetic study of free radical scavenging action of the prenylquinols in solvents of different polarity was performed. The pseudo-first-order rate constants, k, for the reaction of the prenylquinols with 1,1-diphenyl-2-picrylhydrazyl (DPPH) in hexane showed that their scavenging activity changes in the order VK2H2 > VK1H2 > alpha-TQH2 > PQH2-9 > alpha-T > UQH2-10, being the highest in hexane and methanol, whereas in acetone and ethyl acetate the scavenging activity appeared much lower. The reaction rate constants, k, were apparently not dependent on the solvent polarity. The antioxidant activity of the prenylquinols in natural membranes is discussed.

Effect of beta-carotene on structural and dynamic properties of model phosphatidylcholine membranes. II. A 31P-NMR and 13C-NMR study

Spin label EPR studies (Strzałka and Gruszecki (1994) Biochim. Biophys. Acta 1194, 138-142) revealed that beta-carotene affects structural and dynamic properties of model dipalmitoylphosphatidylcholine (DPPC) membranes (multilamellar liposomes) more than polar carotenoid lutein. NMR measurements presented in this paper demonstrate that beta-carotene exerts different effect on various groups of the DPPC molecule. It was found that beta-carotene: (1) increases motional freedom of lipid headgroups as revealed by means of 31P-NMR; (2) increases motional freedom of alkyl chains forming the hydrophobic core of the membrane greater than that of a choline moiety as revealed by means of 13C-NMR. In all cases the effect of beta-carotene with respect to the dynamics of DPPC molecules is found to be more pronounced below the main phase transition temperature than in the membrane's fluid state. The influence of beta-carotene on the molecular dynamics of DPPC molecules is discussed in terms of localization and orientation of this pigment within lipid bilayer.

Effect of beta-carotene on structural and dynamic properties of model phosphatidylcholine membranes. I. An EPR spin label study

The influence of beta-carotene on structural and dynamic properties of model membranes (multilamellar liposomes) prepared of dipalmitoylphosphatidylcholine was investigated. It was found that beta-carotene: (1) decreases order within crystalline state of the membrane; the effect of beta-carotene was more pronounced than in the case of the polar carotenoid, lutein, as revealed by means of spin label EPR; (2) increases penetration, stronger than lutein, of apolar molecules into the membrane as indicated by greater partition coefficient of 5-doxyldecane; (3) increases correlation times tau B tau C stronger than lutein. In all cases the effect of beta-carotene on a membrane was more pronounced at crystalline state than at fluid state. On this basis a hypothesis is proposed that beta-carotene plays a physiological function in the fluidization of chloroplast membranes in a chilling stress to the photosynthetic apparatus.

Fluorescence properties of plastoquinol, ubiquinol and alpha-tocopherol quinol in solution and liposome membranes

It was found that plastoquinol-9, ubiquinol-10 and alpha-tocopherol quinol show intrinsic fluorescence in organic solvents and in liposomes. Their fluorescence spectra in solution showed the presence of one emission band with maximum intensity in the range 319.0-327.0 nm for plastoquinol and 321.5-326.5 nm for alpha-tocopherol quinol, which is the longest wavelength shifted in polar solvents. The emission band at about 371 nm for ubiquinol was not sensitive to solvent polarity. For all three prenylquinones the fluorescence quantum efficiency changed significantly in solvents of different polarities, being the highest in ethanol and the lowest in hexane in the case of plastoquinol and alpha-tocopherol quinol, whereas ubiquinol fluorescence showed the opposite effect. These spectral parameters were applied to determination of prenylquinol localization in liposome membranes.

Linear dichroism and molecular orientation in Langmuir-Blodgett films of plastoquinones and alpha-tocopherol quinone

The linear dichroism of monolayers of plastoquinone-9, plastoquinone-3 and alpha-tocopherol quinone has been measured. The angle between the transition moments and the plane of the solid support was found to lie between 24 degrees and 28 degrees for the investigated prenylquinones. The possible orientation of quinone rings in a monolayer state has been discussed.

Monolayer study of plastoquinones, alpha-tocopherol quinone, their hydroquinone forms and their interaction with monogalactosyldiacylglycerol. Charge-transfer complexes in a mixed monolayer

The surface pressure-area isotherms of pure plastoquinone-9 (PQ-9), plastoquinone-3 (PQ-3), alpha-tocopherol quinone (alpha-TQ), their reduced (hydroquinone) forms and mixtures of these molecules with monogalactosyldiacylglycerol (MGDG) have been studied by a monolayer technique. The collapse pressures of all hydroquinones (QH2) were higher than those of the corresponding quinones (Q), the difference being highest between PQ-9 and PQH2-9. The limiting molecular areas of hydroquinones were higher than those of the corresponding quinones except for alpha-TQH2. All Q-QH2 mixtures showed miscibility throughout the whole range of the components' ratios. There was no deviation from the additivity rule observed for any of the Q-QH2 mixture, as well as for the mixtures of MGDG with PQ-3, PQH2-9, alpha-TQ and alpha-TQH2. On the other hand, PQ-9/MGDG and PQH2-3/MGDG mixtures showed positive and negative deviations, respectively. All the isotherms of Q-MGDG and QH2-MGDG mixtures showed a kink point above the collapse pressure of the Q or QH2 examined, indicating that with the increase in surface pressure, Q or QH2 were gradually squeezed out from the monolayer. The percent content of Q and QH2 in the monolayer as a function of surface pressure was also calculated. The hydroquinones were more difficult to remove from monolayers than the corresponding quinones, and among the investigated quinones, PQ-9 was most easily and alpha-TQ most difficulty squeezed out. The surface pressure-area isotherms of the three-component mixtures of PQ-9/PQH2-9/MGDG showed a shift to lower molecular areas in comparison with the corresponding two-component mixtures, especially at higher surface pressures. This indicates that the presence of PQ-9 lowered the PQH2-9 content in the monolayer, especially at higher pressures, which was explained by charge-transfer complex formation upon interaction of PQ-9 with PQH2-9. The comparison of surface potential-area isotherms of PQ-9/PQH2-9/MGDG mixtures with those of the corresponding binary mixtures also suggest charge-transfer interaction between PQ-9 and PQH2-9. The orientation and localization of the investigated quinones and quinols in the thylakoid membrane and significance of charge-transfer interactions in functioning of PQ-9 has been discussed.

Study on the Parameters Affecting Oxygen Release Time Measurements by Amperometry

The amperometric analysis of photosynthetic oxygen evolution in thylakoid membrane preparations of tobacco, sedimented on a large surface electrode, shows that the oxygen signal is preceded by a lag phase of 1.2 ms. As the used tobacco lamellar systems have an average diameter of 4 - 5 μm this lag phase is interpreted to be due to an average distance of 2.4 μm between oxygen emitting sources and the electrode surface. This interpretation of the lag phase is substantiated by the fact that photosystem I-mediated oxygen uptake in the same preparation measured with the same amperometric technique exhibits the same lag phase although the kinetic uptake parameters are considerably slower than those of oxygen evolution due to the water-splitting reaction. The analysis of the oxygen evolution signal shows that the sedimentation time i.e. the quality of the contact of the source with the electrode is decisive for the measured value for the oxygen release time, which with this method without much effort comes out to be certainly not longer than 1.5 ms. A computer simulation shows that the distance of the oxygen emitting layer from the electrode as well as its thickness and the actual release time are variables which influence practically all parameters (signal shape, amplitude etc.) of such amperometric signals. From this it appears that the determined apparent experimental parameters of oxygen evolution kinetics contain deformations due to the thickness of the sample and the diffusion distance from the electrode. An extrapolation calculated for a sample of infinite thinness separated from the electrode by a minimal distance of 0.001 μm with τ of 5.5 ms yields a lower limit value for the half-rise time of 0.5 ms, a value which has been experimentally determined by EPR oximetry (K. Strzalka, T. Walczak, T. Sarna, and H. M. Swartz, Arch. Biochem. Biophys. 281, 312 (1990)).

Transport of proteins from cytoplasm into plastids in chloramphenicol-treated bean leaf discs : Autoradiographic evidence

Leaf discs from etiolated bean plants were found to incorporate [(3)H]lysine into 80 S ribosomesynthesized proteins in the presence of chloramphenicol (100 mg l(-1)) when exposed to light. After a 7 min pulse of [(3)H]lysine, the discs were transferred to the same medium but with nonradioactive lysine, and postincubation was carried out for 24 h. The number of silver grains over the plastids, after the first period of a lag phase, indicates a large increase between 12 and 24 h of postincubation. Simultaneously, the labeling of the cytoplasm becomes reduced during that period. The results show that during inhibition of the protein formation within plastids, the synthesis of plastid-destined proteins in cytoplasm, as well as their transport into plastids, can still proceed.

Temperature effect on growth, and selected parameters of Phaeodactylum tricornutum in batch cultures

The effect of optimal and stress temperatures on the growth kinetics of the Phaeodactylum tricornutum CCAP/1055/1 strain (a model diatom with a known genome sequence) in batch cultures was examined. The analysis of the obtained results showed two phases of culture growth. There were significant positive correlations between OD increase of chlorophyll a chlorophyll c and protein concentration at different temperatures. The Fv/Fm parameter achieved a maximum level on the 6(th) or 7(th) day and then decreased to the values registered on the first day of observation. Genetic material undergoes gradual degradation 10 days after inoculation. The size of the cells was invariable.

Expression of three diadinoxanthin de-epoxidase genes of Phaeodacylum tricornutum in Escherichia coli Origami b and BL21 strain

In the diadinoxanthin cycle the epoxy group is removed from diadinoxanthin and diatoxanthin is created. This conversion takes place e.g. in diatoms with the involvement of the enzyme diadinoxanthin de-epoxidase. In one of the diatom species, Phaeodactylum tricornutum (CCAP 1055/1 strain with genome sequenced) three de-epoxidase genes (PtVDE, PtVDL1, PtVDL2) have been identified, but only one of them (PtVDE) corresponds to violaxanthin de-epoxidase, an enzyme which is commonly found in higher plants. In these studies, the expression of two de-epoxidase genes of another Phaeodactylum tricornutum strain (UTEX 646), which is commonly used in diatom studies, were obtained in Origami b and BL21 E. coli strains. The molecular masses of the mature proteins are about 49 kDa and 60 kDa, respectively, for VDE and VDL2. Both enzymes are active with violaxanthin as a substrate.