Spectroscopic studies of green-bacterial reaction center

• Project/Area Number: 08044223
• Research Category: Grant-in-Aid for international Scientific Research
• Allocation Type: Single-year Grants
• Section: Joint Research
• Research Field: 植物生理
• Research Institution: Waseda University
• Principal Investigator: SAKURAI Hidehiro Waseda Univ., Sch.of Education, Professor, 教育学部, 教授 (10063645)
• Co-Investigator(Kenkyū-buntansha): BRETTEL Klaus CEA (France), DBCM,Researcher, DBCM, researcher ; SETIF Pierre CEA (France), DBCM,Research director, DBCM, research d ; INOUE Kazuhito KANAGAWA Univ., Fac.of Science, Lecturer, 理学部, 講師 (20221088) ; KUSUMOTO Noriaki Waseda Univ., Sch.of Education, Senior Res.Assoc., 教育学部, 助手 (60277861)
• Project Period (FY): 1996 – 1997
• Project Status: Completed (Fiscal Year 1997)
• Budget Amount: ¥8,700,000 (Direct Cost: ¥8,700,000); Fiscal Year 1997: ¥4,500,000 (Direct Cost: ¥4,500,000); Fiscal Year 1996: ¥4,200,000 (Direct Cost: ¥4,200,000)
• Keywords: photosynthesis / reaction center / green sulfur bacteria / cytochrome / iron-sulfur cluster / flash-absorption spectroscopy / menaquinone-7 / Fe-Sセンター / 閃光分光

Research Abstract

Electron transfer kinetics in the reaction center (Re) complex from the green sulfur bacterium Chlorobium tepidum which binds two cytochrome c (cyt c) were studied by flash-absorption spectroscopy. Photooxidized P84O^+ was reduced 95% and 80% after 1 ms by cyt c with t^<1/2> of about 65 mus and 100 muz s after the 1st and the 2nd flashes, respectively . The observed rates, the establishment of redox equilibrium after each flash and the total amount of photooxidizable cyt c are consistent with the presence of 2 equivalent cyt c per photooxidizable P840. The data were well fitted assuming a midpoint potential difference of -53 mV for electron transfer from one cyt c to P8404^+, * Em being independent of the oxidation state of the other cyt c. These observations support a model with 2 monoheme cyt c which are symmetrically arranged around the RC core. The purified RC complex binds 0.6-1.2 menaquinone-7 (MQ) . However, no transient signal due to MQ could be observed between 360 and 450 nm in the time window from 10 ns to 4 mu s. On the acceptor side, purified RC can stably hold up to 3 electrons in the mu s time range.
However, after the 4th flash, a charge recombination reaction with t^<1/2> of 20 ns was first observed. From our data, there is no evidence for involvement of MQ in charge separation in the RC of green sulfur bacteria.

Research Products

• [Publications] Seo, D., Kusumoto, N., Sakurai, H., Brettel, K., Setif, P.: "Proceedings of the XIth International Conference on Photosynthesis (Garab, G.Ed.)" Kluwer Academic Publishers, Dordrecht, 4 (1998)
  • Description: 「研究成果報告書概要(和文)」より
• [Publications] Seo, D., Kusumoto, N., Sakurai, H.Brettel, K., Setif, P.: Proceedings of the XIth International Conference on Photosynthesis (Garab, G.Ed.). Kluwer Academic Publishers, Dordrecht, 4 (1998)
  • Description: 「研究成果報告書概要(欧文)」より
• [Publications] Sakurai, H., Kusumoto, N.: "Electronic and vibrational structure of the radical cation of P840 in the putative homodimeric reaction center from Chlorobium tepidum as studied by FTIR spectroscopy" Biochemistry. 35・48. 15428-15435 (1996)
• [Publications] Noguchi,T.,Kusumoto,N.,Inoue,Y.,Sakurai,H.: "Electronic and vibrational structure of the radical cation of P840 in the putative homodimeric reaction center from chlorobium tepidum as studied by FTIR spectroscopy" Biochemistry. 35. 15428-15435 (1996)