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Biomedical subjects

A A Kononenko

Publications and source records attributed to A A Kononenko.

At least 55 records · Page 3Linked to original sources
PubMedDate not supplied

[Isolation and characterization of photochemical properties of the photosynthetic reaction centers from Rhodopseudomonas shperoides, strain 1760-1].

Photosynthetic reaction centres were isolated from the cells of Rhodopseudomonas spheroides, strain 1760-1, using sodium dodecyl sulphate. The preparations purified by precipitation with ammonium sulphate showed absorbance ratios of A280 : A800=2.1. and A765 : A800 : A870=1 : 2 : 1; about 75% of the bacteriochlorophyll absorbing at 870 nm (P870) were photochemically active. Both absolute and difference "light minus dark" absorption spectra were obtained for the reaction centre suspensions and vacuum-dried films at room and low temperatures. Shift to the longer wavelength of the 870 nm absorption band resulting from temperature lowering suggests the existence of temperature-determined conformations of the bacteriochlorophyll-protein complex of the reaction centres. Characteristic time of an electron transfer from the photoexcited P870 to the primary intermediate of photochemical process as evaluated from the data of pulsed laser fluorometry of the reaction centres was found to be (21--15)+/-8 picoseconds. The oxidized P870 dark reduction kinetics dependence on the actinic light intensity gives evidence for the functioning of heterogeneous pool of the secondary electron acceptors in the reaction centre preparations. Filling in of this pool with electrons is decreased under temperature lowering or vacuum drying and its electron capacity is limited under isooctane treatment resulting in ubiquinon extraction. The ability of the reaction centre preparations to catalyze the photochemical oxidation of iminoxyl aromatic radical was demonstrated.

Bacteriochlorophylls↗
PubMedDate not supplied

[Spectral position of the principal absorption band of pigment complex P870 and the kinetics of photo-induced oxidoreductions in the reaction centers and chromatophores of purple bacteria with preparations at different temperatures and having different degrees of hydration].

In isolated photosynthetic reaction centres of Rps. spheroides and chromatophores R. rubrum the spectral position of the longest wavelength absorption band of P870, effectiveness of electron removal from the photochemical pair (P870 -- primary electron acceptor, A1) and the rate constant for recombination of photooxidized P870 with photoreduced A1 undergo marked and fully reversible changes over the temperature interval from +20 to -70 degrees. Dehydration of the samples has the effect similar to that induced by temperature lowering. The data suggest that the spectral position of the main maximum of pigment complex P870 absorption band may be regarded as a sensitive inner probe of the structure-functional state of the investigated preparations.

Bacterial Chromatophores↗
PubMedDate not supplied

[Possible role of macromolecular components in the functioning of photosynthetic reaction centers of purple bacteria].

The temperature dependencies of the photoconversion of pigments P870--P890 were studied using isolated chromatophores and photosynthetic reaction centres (RC's) of purple bacteria. The samples were prepared by extraction with organic solvents (light petroleum and a combination of light petroleum and methanol) and modified through cross-linking the functional groups of proteins by treatment with glutaraldehyde or denatured by various physical and chemical treatments. The data provide further evidence that the pool of RC secondary acceptors is formed by the compounds of quinone nature located in the hydrophobic surrounding. Similar molecules localized in a more polar medium act as primary acceptors. The findings indicate on the essential role of macromolecular components in the RC's functioning and also suggest that the photochemical charge separation is conformation-controlled.

Bacterial Chromatophores↗
PubMedDate not supplied

[Conformational regulation of functional activity of photosynthetic membranes of purple bacteria].

In reaction centres of photosynthetic membranes of R, rubrum the efficiency of redox interactions of the photoreduced primary electron acceptor with secondary acceptors and photooxidized bacteriochlorophyll has a marked and reversible dependence on temperature over the range from -20 degrees to -80 degrees. Similar temperature dependences were observed for correlation times of the rotational diffusion of a spin probe bound to the hydrophobic region of the membrane and of a spin label bound to SH-groups of the protein constituent of the membrane, as well as for characteristics of resonance absorption of the Mössbauer probe (57Fe), embedded in the membrane by biosynthesis. Using the same indicators of intramolecular mobility, a correlation has been observed between photoactivity and structure of the membrane in experiments involving hydratation changes of samples. The data suggest the existence of a close interrelationship between the conformational mobility of the constituents of the photosynthetic membrane and their specific reaction capacity.

Bacteriochlorophylls↗
PubMedDate not supplied

[Effect of temperature on the phototransformation of purple sulfur bacteria bacteriochlorophylls and isolated chromatophores].

Photobleaching of P890 was shown to be independent of temperature within the range of +20 to -160 degrees C in purple sulphur bacteria and isolated chromatophores under oxidative conditions; therefore changes in the absorption at 890 nm are due to the primary photoact. No changes were detected in the absorption at 850 nm upon a slight decrease of temperature, which suggested the absorption at 850 nm upon a slight decrease of temperature, which suggested the conformation nature of these changes. The effect of temperature, which suggested the conformation nature of these changes. The effect of temperature on the photoinduced changes of absorption under reductive conditions seems to be due to the electron transport and the accompanying processes being blocked. The effect of temperature on the kinetics of P890+ reduction in the darkness under conditions when the cytochromes are preliminarily oxidized is determined by the participation of the secondary electron acceptors in this process. A decrease in temperature leads to blocking the transport of electrons from the primary acceptor to the secondary acceptors, which is expressed by a gradual disappearance of a slow component in the kinetics of p890+ reduction in the disappearance of a slow component in the kinetics of P890+ reduction in the darkness and by the intensification of a fast component resulting from the darkness and by the intensification of a fast component resulting from the interaction between the primary acceptor and P890+. Methodical aspects of absorption differential spectrophotometry of photosynthesizing organisms at low temperatures are discussed.

Bacteria↗
PubMedDate not supplied

[Molar extinction of pigment in the reaction center of photosystem II chloroplasts].

The absolute spin number in the Photosystem I chloroplast fragments from Vicia faba plant photooxidized in the presence of silicomolybdate has been carefully measured by means of camparison of ESR signals of P680-centers and of nitroxyl free radical aqueous solution. The data obtained together with simultaneous measurement of light-induced bleaching centered at 680 nm have been used to determine the molar extinction of reduced P680-center epsilon680 = 0.66 . 10(5) M-1 cm-1.

Binding Sites↗
PubMedDate not supplied

[Conformational mobility and functional activity of photosynthetic reaction centers of Rhodopseudomonas sphaeroides].

In pigment-protein complexes of photosynthetic reaction centres (RC's), extracted from chromatophore membranes of Rps. sphaeroides with sodium dodecylsulphate, functional activity and intramolecular mobility were studied as a function of temperature and hydration by use of the technique of optical absorbance and ESR spectroscopy. Over the studied temperature range from +20 to -120 degrees C and at a relative humidity (P/Ps) from 0.9 to 0.1, there observed a close interrelationship between reversible kinetic changes of direct and backward redox-reactions of the photo-reduced endogeneous acceptor of quinone nature and the effective parameter of the correlation time of the rotational diffusion of the hydrophobic spin probe as well as of spin labels chemically bound to SH- and COOH-groups of amino acid residues of the RC's protein. The findings support the view that the conformational dynamics in the RC controls the effectiveness of the primary processes of stabilization of photochemically separated charges.

Bacterial Chromatophores↗
PubMedDate not supplied

[Kinetic model of the effect of dehydration on electron transfer from membrane-bound cytochrome c to the photosynthetic reaction center].

Amplitude characteristics and kinetics of laser-induced oxidation of high-potential cytochrome CH by a photosynthetic reaction center (RC) were investigated in Ectothiorhodospira shaposhnikovii chromatophore preparations of various humidity. It is shown that the diminuition of the amount of oxidized cytochrome and the decrease of the rate of the reaction on lowering the preparation humidity can be explained in terms of the concept of conformation-controlled electron transfer within the CH-RC complex. A model is suggested which predicts that the reversible transition of the complex from one conformational state which allows electron transfer ("contact" state) to the other in which the transfer is impossible ("non-contact" state) is the result of drying (or low temperature) induced changes in the electron tunnelling path in the region of "contact" of the cytochrome CH and RC protein globules.

Bacteria↗
PubMedDate not supplied

[Polarization of photosynthetic membranes and reaction centers of Rhodopseudomonas sphaeroides 1760-1 in an external electrical field].

Electric fields as high as 10(5) V/cm cause polarization of chromatophores and reaction centre films prepared from photosynthesizing bacteria. Photosynthetic pigments, carotenoids in particular, the absorption spectra of which are changed in response to electric fields, may serve as an intrinsic indicator of the development of a polarized state. Polarization occurs due to changes in orientation and spacial position of different charge groups and particles. The field-induced polarized state can be fixed up by exposure to low temperature (-120 degrees C). While heating the system relaxes to the initial state and this can be seen as a current in an electric circuit. The effects of hydration, chemical modification or heat treatment on current indicate the involvement of macromolecule components in the formation of a polarized state, In light-adapted samples the polarization effect is markedly greater and this can indicate that conformational changes occur during the primary photoact. It is supposed that polarization might be implicated in the stabilization of separated charges and in the storage of energy.

Bacterial Chromatophores↗
PubMedDate not supplied

[Temperature dependence of protein globule polarization and electron transport in preparations of photosynthetic reaction centers from Rhodopseudomonas sphaeroides].

Differential "light-minus-dark" spectra were obtained for reaction center (RC) preparations cooled in the light and in the dark at 77 K. The two types of preparations were found to display different spectral features in the spectral regions 760-770, 790-810, 880-990 nm. Differences in the spectra of the two types were found to exist in preparations cooled to temperatures below 120-100 K, whereas at temperatures above 130 K such differences were not observed. The observed spectral changes may be associated with the polarization processes occurring in the RC globule. Samples cooled in the light and in the dark show different temperature dependencies of the efficiency of electron transfer to the secondary quinone acceptor. The differences are irreversible after cooling to temperatures below 170 K, and reversible after cooling to 180-200 K. It is postulated that the observed kinetic changes are reflections of changes in the configuration of the acceptor complex of the RC. The possible existence of a correlation between the polarization processes in the protein globule and the structural configurations of the RC is discussed.

Bacterial Proteins↗
PubMedDate not supplied

[Effect of dehydration on electron transport from membrane-bound cytochromes c to bacteriochlorophyll of the photosynthetic reaction center in chromatophores of purple thiobacteria].

A method is proposed for spectroscopic probing photo-induced reversible oxidation-reduction changes of high-potential cytochrome in chromatophore films of various humidity. On these preparations of Ect. shaposhnikovii and Chr. minutissium it was found that the characteristic time of cytochrome oxidation, tau, in samples with a high degree of humidity (P/Ps = 0.75) is 2-3 mus, which is close to that seen under physiological conditions (a suspension of intact cells or chromatophores). It was found that under continuous or pulsed illumination the lowering of the relative humidity from 0.75 to 0.15 P/Ps results in a reversible decrease in the amount of cytochrome molecules that can undergo photooxidation. The fraction of cytochrome pool that retains its activity shows a rate of oxidation which remains almost without change. The observed hydration effect and its involvement in the control of the photo-induced oxidation of cytochromes must be taken into account when a model of the molecular mechanism of this process is constructed on the basis of the electron tunneling theory. It is also shown that the dark-reduction kinetics of high-potential cytochrome consist of two components: a fast component with t1/2 = 1-3s which is independent of the sample humidity and a slow component with t1/2 = 5-20 s whose lifetime increases by a factor of 3-5 on reducing the humidity. At a high degree of humidity (P/Ps = 0.75-0.5), the kinetics of cytochrome dark-reduction exhibits only the slow component. The fast component is probably associated with the return of an electron from the primary ferroquinone acceptor and the slow component seems likely to be due to the direct transfer of an electron from exogenous electron donor to the cytochrome.

Bacterial Chromatophores↗
PubMedDate not supplied

[Thermodynamic characteristics of the interaction of high-potential cytochrome with dimer of bacteriochlorophyll in the reaction centers of Ectothiorhodospira shaposhnikovii chromatophores].

Kinetics of dark reduction of cytochrome CH (E7=290 mV) after its photoinduced oxidation chromatophores of E. shaposhnikovii at 110-210 K is analysed. A ratio is derived which describes dark reduction of cytochrome. This ratio makes it possible to determine the value of free energy of the electron transfer between cytochrome and bacteriochlorophyll dimer of the reaction centre (Bchl)2. The values of enthalpy and entropy of the transition under study at the temperatures below 210 K are equal to 1,67 kJ M-1 and 26,8 J M-1 K-1 correspondingly. A change of free energy obtained by linear extrapolation to the room temperature equals 9,71 kJ M-1. This value well agrees with the value 9,63 kJ M-1 obtained from the results of direct potentiometric titration of photoinduced redox transformations CH and (Bchl)2.

Bacterial Chromatophores↗