ABSTRACT: Laser-induced temperature jump experiments were used for testing the rates of thermoinduced conformational transitions of reaction center (RC) complexes in chromatophores of Chromatium minutissimum. The thermoinduced transition of the macromolecular RC complex to a state providing effective electron transport from the multiheme cytochrome c to the photoactive bacteriochlorophyll dimer within the temperature range 220-280 K accounts for tens of seconds with activation energy 0.166 eV/molecule. The rate of the thermoinduced transition in the cytochrome-RC complex was found to be three orders of magnitude slower than the rate of similar thermoinduced transition of the electron transfer reaction from the primary to secondary quinone acceptors studied in the preceding work (Chamorovsky et al. in Eur Biophys J 32:537-543, 2003). Parameters of thermoinduced activation of the electron transfer from the multiheme cytochrome c to the photoactive bacteriochlorophyll dimer are discussed in terms of cytochrome c docking onto the RC.
European Biophysics Journal 08/2007; 36(6):601-8. · 2.14 Impact Factor
ABSTRACT: Methods of laser-induced temperature jumps and fast freezing were used for testing the rates of thermoinduced conformational transitions of reaction center (RC) complexes in chromatophores and isolated RC preparations of various photosynthesizing purple bacteria. An electron transfer reaction from primary to secondary quinone acceptors was used as a probe of electron transport efficiency. The thermoinduced transition of the acceptor complex to the conformational state facilitating electron transfer to the secondary quinone acceptor was studied. To investigate the dynamics of spontaneous decay of the RC state induced by the thermal pulse, the thermal pulse was applied either before or during photoinduced activation of electron transport reactions in the RC acceptor complex. The maximum effect was observed if the thermal pulse was applied against the background of steady-state photoactivation of the RC. It was shown that neither the characteristic time of the thermoinduced transition within the temperature range 233-253 K nor the characteristic time of spontaneous decay of this state at 253 K exceeded several tens of milliseconds. Independent support of the estimates was obtained from experiments with varied cooling rates of the samples tested.
European Biophysics Journal 10/2003; 32(6):537-43. · 2.14 Impact Factor
ABSTRACT: NMR spectra and T1, T2 relaxation times for 1H, 13C and 31P nuclei in membranes of R. rubrum and Rb. sphaeroides recorded at different relative humidity, as well as hydration curves and electron transfer efficiency of these membranes
and membranes of E. shaposhnikovii, reveal complicated relations between structural-dynamic and functional characteristics. A number of sites of the electron
transfer chain are shown to be under the control of structural-dynamic mechanisms. Different parameters characterizing these
membranes at low humidity and during hydration have been established. These findings and analysis of the data from model systems
reveal four different stages of hydration. Each of them is associated with specific changes in structure, dynamics, and function
of photosynthetic membranes and their components. In the first stage the hydration of some polar groups leads to local changes
in the dynamics of the protein component and this influences the recombination between photoactive pigment P and intermediate
acceptor QA. The second stage is induced by incorporation of water molecules into the hydrogen bonds between the polar head groups of
the lipids and within macromolecules. This results in changes of the dynamics of the membranes, the efficiency of the electron
transfer between the quinones and the efficiency of photooxidation of cytochrome c. In the third stage all polar groups are
hydrated owing to the appearance of free water with a high dielectric constant. This makes possible lateral mobility of membrane
components and changes in distances between the interacting macromolecular components. Therefore, the regulation of photosynthetic
processes can be mediated with the participation of mobile carriers. Finally, in the fourth stage, complete humidification
provides conditions for regulation of photosynthesis at the cell level. The mechanisms influencing these processes and the
efficiency and regulation of electron transfer in various parts of the photosynthetic chain are discussed.
European Biophysics Journal 10/1997; 26(6):461-470. · 2.14 Impact Factor