Effect of Dipyridamole on Membrane Energization and Energy Transfer in Chromatophores of Rba. sphaeroides.

Effect of dipyridamole (DIP) at concentrations up to 1 mM on fluorescent characteristics of light-harvesting complexes LH2 and LH1, as well as on conditions of photosynthetic electron transport chain in the bacterial chromatophores of Rba. sphaeroides was investigated. DIP was found to affect efficiency of energy transfer from the light-harvesting complex LH2 to the LH1-reaction center core complex and to produce the long-wavelength ("red") shift of the absorption band of light-harvesting bacteriochlorophyll molecules in the IR spectral region at 840-900 nm.

The effect of some antiseptic drugs on the energy transfer in chromatophore photosynthetic membranes of purple non-sulfur bacteria Rhodobacter sphaeroides.

Chromatophores of purple non-sulfur bacteria (PNSB) are invaginations of the cytoplasmic membrane that contain a relatively simple system of light-harvesting protein-pigment complexes, a photosynthetic reaction center (RC), a cytochrome complex, and ATP synthase, which transform light energy into the energy of synthesized ATP. The high content of negatively charged phosphatidylglycerol (PG) and cardiolipin (CL) in PNSB chromatophore membranes makes these structures potential targets that bind cationic antiseptics. We used the methods of stationary and kinetic fluorescence spectroscopy to study the effect of some cationic antiseptics (chlorhexidine, picloxydine, miramistin, and octenidine at concentrations up to 100 μM) on the spectral and kinetic characteristics of the components of the photosynthetic apparatus of Rhodobacter sphaeroides chromatophores.

Relaxation processes accompanying electron stabilization in the quinone acceptor part of Rb. sphaeroides reaction centers.

The temperature dependence of the dark recombination rate in photooxidized bacteriochlorophyll (P) and photoreduced quinone acceptors (ubiquinones) Q and Q of photosynthetic reaction centers of purple bacteria Rhodobacter sphaeroides (Rb. sphaeroides) was studied. Photoinduced changes in the absorption were detected in the Q absorption band of photooxidized bacteriochlorophyll at 600 nm and in the bands corresponding to the redox changes of ubiquinones at 335 and 420-450 nm.

Influence of trehalose on high-temperature stability of the photosynthetic reaction centers.

The effect of heating at 65°C for 20 min on the absorption spectra and kinetics of the dark recombination of charges separated between photoactive bacteriochlorophyll and quinone acceptors was studied in dry films of bacterial photosynthetic reaction centers (RCs), RC films in polyvinyl alcohol, and trehalose. A pronounced protective effect of trehalose against pheophytinizaiton of molecules bacteriochlorophylls in RC structure and in maintaining their higher photochemical activity was found.

Temperature Dependence of Tryptophan Fluorescence Lifetime in Aqueous Glycerol and Trehalose Solutions.

The temperature dependences of tryptophan fluorescence decay kinetics in aqueous glycerol and 1 M trehalose solutions were examined. The fluorescence decay kinetics were recorded in the spectral region of 292.5-417.

Generation of radical form of dipyridamole at illumination of photosynthetic reaction centers of Rb. sphaeroides.

The study of the effect of vasodilator, antiplatelet agent, and inhibitor P-glycoprotein dipyridamole (DIP) on the functioning of the transmembrane protein of the reaction center (RC) of Rb. sphaeroides showed that the activation of RC by constant light generates the DIP radical cation, which significantly affects the kinetics of recombination of charges divided between photoactive bacteriochlorophyll and quinone acceptors. Thus, the antioxidant properties of DIP may affect the functional activity of membrane proteins, and this apparently should be taken into account in the studies of the mechanisms of therapeutic action of this drug.

[Effect of chromate ions on marine microalgae Phaeodactylum tricornutum].

Effect of chromate ions on the culture of a marine diatom Phaeodactylum tricornutum was studied using an M-PEA-2 fluorimeter, which carries out simultaneous measurement of fluorescence induction and redox transformations of the P700 pigment within a millisecond range. Chromate ions were shown to inhibit electron transport in PS II and decrease the rate of QА reduction. This results in decreased values of the quantum yield of electron transport in PS II (ϕEo) and performance index (PI ABS), lower rates of P700 reduction, and increased energy (DI0/RC) and ΔpH-dependent nonphotochemical quenching (q E ).

Purple-bacterial photosynthetic reaction centers and quantum-dot hybrid-assemblies in lecithin liposomes and thin films.

Quantum dots (QDs) absorb ultraviolet and long-wavelength visible light energy much more efficiently than natural bacterial light-harvesting proteins and can transfer the excitation energy to photosynthetic reaction centers (RCs). Inclusion of RCs combined with QDs as antennae into liposomes opens new opportunities for using such hybrid systems as a basis for artificial energy-transforming devices that potentially can operate with greater efficiency and stability than devices based only on biological components or inorganic components alone. RCs from Rhodobacter sphaeroides and QDs (CdSe/ZnS with hydrophilic covering) were embedded in lecithin liposomes by extrusion of a solution of multilayer lipid vesicles through a polycarbonate membrane or by dialysis of lipids and proteins dispersed with excess detergent.

The kinetic model for slow photoinduced electron transport in the reaction centers of purple bacteria.

The present work is related to the investigation of slow kinetics of electron transport in the reaction centers (RCs) of Rhodobacter sphaeroides. Experimental data on the absorption kinetics of aqueous solutions of reaction centers at different modes of photoexcitation are given. It is shown that the kinetics of oxidation and reduction of RCs are well described by the sum of three exponential functions.

[Effect of Methylmercury on the Light Dependence Fluorescence Parameters in a Green Alga Chlamydomonas moewusii].

The effect of a dangerous toxic substance, methylmercury, on light dependence curves of chlorophyll fluorescence in Chlamydomonas moewusii was studied. We found low concentration of methylmercury (10(-7) M) to cause a decrease in the relative rate of the non-cyclic electron transport activity of PS 2, a decline in the maximum utilization of light energy (α), and a decline in the saturation light intensity (E(s)). Non-photochemical fluorescence quenching increased after short-term exposure and decreased in the course of prolonged incubation.

Investigation of Stability of Photosynthetic Reaction Center and Quantum Dot Hybrid Films.

The efficiency of interaction (efficiency of energy transfer) between various quantum dots (QDs) and photosynthetic reaction centers (RCs) from the purple bacterium Rhodobacter sphaeroides and conditions of long-term stability of functioning of such hybrid complexes in film preparations were investigated. It was found that dry films containing RCs and QDs and maintained at atmospheric humidity are capable to keep their functional activity for at least some months as judging by results of measurement of their spectral characteristics, efficiency of energy transfer from QDs to RCs, and RC electron-transport activity. Addition of trehalose to the films giving them still greater stability is especially expressed for films maintained at low humidity.

Properties of hybrid complexes composed of photosynthetic reaction centers from the purple bacterium Rhodobacter sphaeroides and quantum dots in lecithin liposomes.

Quantum dots (QDs) can absorb ultraviolet and long-wavelength light energy much more efficiently than natural light-harvesting proteins and transfer the excitation energy to photosynthetic reaction centers (RCs). Inclusion into liposomes of RC membrane pigment-protein complexes combined with QDs as antennae opens new opportunities for using such hybrid systems as a basis for artificial energy-transforming devices that potentially can operate with greater efficiency and stability than devices based only on biological components. RCs from Rhodobacter sphaeroides and QDs with fluorescence maximum at 530 nm (CdSe/ZnS with hydrophilic covering) were embedded in lecithin liposomes by extrusion of a solution of multilayer lipid vesicles through a polycarbonate membrane or by dialysis of lipids and proteins dispersed with excess detergent.

[Effect of silver nanoparticles on the parameters of chlorophyll fluorescence and P700 reaction in the green alga Chlamydomonas reinhardtii].

Acute toxicity of silver nanoparticle (AgNP) for photosynthesis in Chlamydomonas reinhardtii was studied using an M-PEA2 fluorimeter. Analysis of the fluorescence induction curves in the presence of AgNP at low concentrations revealed inhibited electron transport in the PS2 photosystem and increased content of Q(B)-nonreducing centers. No direct effect of AgNP on the reactions of P700 oxidation in PS1 was found, while energization of the photosynthetic membranes was affected.

[On the electron stabilization within the quinone acceptor part of Rhodobacter sphaeroides photosynthetic reaction centers].

The time evolution of the photoinduced differential absorption spectrum of isolated Rhodobacter sphaeroides photosynthetic reaction centers was investigated. The measurements were carried out in the spectral region of 400-500 nm on the time scale of up to 200 microseconds. The spectral changes observed can be interpreted in terms of the effects of proton shift along hydrogen bonds between the primary quinone acceptor and the protein.

Singlet oxygen generation in the reaction centers of Rhodobacter sphaeroides.

Singlet oxygen (1O2) generation in the reaction centers (RCs) of Rhodobacter sphaeroides wild type was characterized by luminescent emission in the near infrared region (time resolved transients and emission spectra) and quantified to have quantum yield of 0.03 +/- 0.005.

[A study of protein structure changes during hydration by means of diffuse X-ray scattering. II. Fourier transform analysis of X-ray scattering data].

Radial distribution functions were deduced by Fourier transform analysis of angular dependences of diffuse x-ray scattering intensities for the following proteins with different hydration degree: water-soluble a-protein myoglobin, water-soluble alpha+beta protein lysozyme, and transmembrane proteins of photosynthetic reaction centers from purple bacteria Rhodobacter sphaeroides and Blastochlorii viridis. The results of Fourier analysis of x-ray scattering intensities give the quantitative characteristics of the mechanisms underlying the influence of water on the formation of biomacromolecules. Water, on the one hand, weakens the intraglobular hydrogen bond net, loosens the protein structure, and increases the internal conformational dynamics.

[The temperature dependence of high-resolution 1H NMR spectra of Rhodobacter sphaeroides photosynthetic reaction centres in a temperature range of 25-40 degrees C].

High-resolution 1H-NMR spectra registered within a temperature range of 25-40 degrees C revealed a nonmonotonous dome-shaped temperature dependence of the ratio between integral NMR signal intensities determined at ppm intervals 2.5-4.5 and 0.

Temporary stabilization of electron on quinone acceptor side of reaction centers from the bacterium Rhodobacter sphaeroides wild type and mutant SA(L223) depending on duration of light activation.

The dark reduction of photooxidized bacteriochlorophyll (P+) by photoreduced secondary quinone acceptor (QB-) in isolated reaction centers (RC) from the bacterium Rhodobacter sphaeroides wild type and mutant strain SA(L223) depending on the duration of light activation of RC was studied. The kinetics of the dark reduction of P+ decreased with increasing light duration, which is probably due to conformational changes occurring under prolonged light activation in RC from the wild type bacterium. In RC from bacteria of the mutant strain in which protonatable amino acid Ser L223 near QB is substituted by Ala, the dependence of reduction kinetics of P+ on duration of light was not observed.

Effects of oxygen on the dark recombination between photoreduced secondary quinone and oxidized bacteriochlorophyll in Rhodobacter sphaeroides reaction centers.

The influence of duration of exposure to actinic light (from 1 sec to 10 min) and temperature (from 3 to 35 degrees C) on the temporary stabilization of the photomobilized electron in the secondary quinone acceptor (QB) locus of Rhodobacter sphaeroides reaction centers (RC) was studied under aerobic or anaerobic conditions. Optical spectrophotometry and ESR methods were used. The stabilization time increased significantly upon increasing the exposure duration under aerobic conditions.

Recombination reduction of photooxidized cytochrome c in reaction centers of Rhodopseudomonas viridis at low temperature.

The temperature dependence of dark reduction of photooxidized cytochrome c was studied in isolated preparations of Rhodopseudomonas viridis reaction centers. Within the range from room temperature to approximately 260 K this process was found to be mediated by thermal diffusion of exogenous donor molecules, whereas at lower temperatures photooxidized cytochrome is reduced as a result of indirect recombination with photoreduced primary quinone acceptor. Kinetic simulation allowed certain thermodynamic characteristics of this reaction to be calculated.