Effects of dehydration and low temperatures on the oxidation of high-potential cytochrome c by photosynthetic reaction centers in Ectothiorhodospira shaposhnikovii |
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| Institution: | 1. Department of Biology, Lomonosov State University, Moscow 119899 U.S.S.R.;2. Institute of Theoretical Physics, Ukrainian Academy of Sciences, Kiev 252130 U.S.S.R.;1. Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y de Estudios Avanzados del IPN, Av. IPN 2508, Zacatenco, Ciudad de México 07360, Mexico;2. Programa de Neurociencias, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Av. de los Barrios 1, Los Reyes Iztacala, Tlalnepantla, 54090 Estado de México, Mexico;1. Interdisciplinary Laboratory of Medical Investigation, School of Medicine, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil;2. Biomarkers Laboratory for Diagnosis and Monitoring, Research Center RenéRachou, FIOCRUZ/MG, Belo Horizonte, Minas Gerais, Brazil;3. Translational Psychiatry Program, Department of Psychiatry and Behavioral Sciences, The University of Texas Health Science Center at Houston, Houston, TX, USA;4. Raul Soares Institute, Hospital Foundation of the State of Minas Gerais (FHEMIG), Belo Horizonte, Brazil;5. Deakin University, IMPACT Strategic Research Centre, School of Medicine, Geelong, Australia;6. Orygen, The National Centre of Excellence in Youth Mental Health, Department of Psychiatry and The Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, Australia;1. Department of Structural Biology, University of Pittsburgh, Pittsburgh, PA 15213, USA;2. Department of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA 15213, USA;3. Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15213, USA;4. Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA 15213, USA;5. Department of Radiation Oncology, University of Pittsburgh, Pittsburgh, PA 15213, USA;6. Center for Free Radical and Antioxidant Health, University of Pittsburgh, Pittsburgh, PA 15213, USA;7. Laboratory of Navigational Redox Lipidomics, IM Sechenov Moscow State Medical University, Moscow 119146, Russian Federation;8. Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands;1. Food Biotechnology Group, Section of Analytical Environmental and Applied Chemistry, Department of Chemistry, University of Patras, GR-26500 Patras, Greece;2. Applied Microbiology and Molecular Biotechnology Research Group, Department of Molecular Biology & Genetics, Democritus University of Thrace, Alexandroupolis 68100, Greece |
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| Abstract: | Effects of temperature and dehydration on the efficiency of electron transfer from membrane-bound high-potential cytochromes ch to the reaction-center bacteriochlorophyll (P-890) in Ectothiorhodospira shaposhnikovii have been studied. A kinetic analysis of the cytochrome oxidation suggests that there are at least two conformational states of the ch-P-890 complex, of which only one allows photoinduced electron transfer from cytochrome to P-890+. Lowering the temperature of dehydration leads to a change in the proportion of the populations in the two conformations. The observed 2-fold deceleration of cytochrome oxidation can be related only to the diminution of the amount of photoactive cytochromes per reaction center. The rate constant for the transfer of an electron from cytochrome ch to bacteriochlorophyll is 2.8 · 105 s−1 and is independent of temperature and dehydration (as estimated within the accuracy of the experiments). The effects produced by low temperature and dehydration are completely reversible. The thermodynamic parameters of the transition of the cytochrome from the nontransfer to electron-transfer conformation were estimated. For room temperature (+ 20°C) in chromatophore preparations, ΔG = −5.4 kJ · M−1, ΔH = 60 kJ · M−1, ΔS = 0.22 kJ · M−1 · K−1. For Triton X-100 subchromatophore preparations, the absolute values of the above parameters are significantly lower: ΔG = −2.8 kJ · M−1, ΔH = 18 kJ · M−1, and ΔS = 0.075 kJ · M−1 · K−1. To a larger extent, the above parameters are diminished for chromatophore preparations in an 80% glycerol solution: ΔG = −1.7 kJ · M−1, ΔH = 6 kJ · M−1, ΔS = 0.025 kJ · M−1 · K−1. The data suggest the hydrophobic character of the forces that maintain the P-890-ch complex in the electron-transfer conformation. The results obtained suggest that electron tunneling within the complex cannot occur until a specific conformational configuration of the complex is formed. The efficiency of cytochrome ch oxidation is determined by the temperature, the degree of dehydration and the environmental conditions, whereas the transfer of an electron itself in the electron-transfer configuration is essentially independent of temperature and hydration. |
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