| Project/Area Number |
05453045
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Inorganic chemistry
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| Research Institution | HIROSHIMA UNIVERSITY |
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Principal Investigator |
AKABORI Kozo Hiroshima University, Faculty of Integrated Arts and Sciences, Professor, 総合科学部, 教授 (80034578)
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| Co-Investigator(Kenkyū-buntansha) |
TESHIMA Keizo Hiroshima University, Faculty of Integrated Arts and Sciences, Associate Profess, 総合科学部, 助教授 (30155452)
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| Project Period (FY) |
1993 – 1994
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| Project Status |
Completed (Fiscal Year 1994)
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| Budget Amount *help |
¥6,700,000 (Direct Cost: ¥6,700,000)
Fiscal Year 1994: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1993: ¥5,300,000 (Direct Cost: ¥5,300,000)
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| Keywords | photosystem II / non-heme iron / photoinhibition / beta-carotene / primary acceptor quinone / 第一安定電子受容体 / カロチノイド |
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| Research Abstract |
The cyclic electron flow in PSII is expected to protect PSII by neutralizing radicals under photoinhibition. PSII core complexes, in which light harvesting chlorophyll-proteins were removed from PSII particles for optical measurements, were applied to Tris-treatment to make photoinhibitory condition by removal of oxygen-evolving complex (TrisRC). The non-heme iron was depleted from TrisRC (-Fe^<2+> -TrisRC) or substituted for Zn^<2+> (Zn^<2+> -TrisRC).
(1) In Tris-treated samples a similair decay kinetics (t_<1/2>=100-200 mu s) was predominantly observed in laser flash induced absorbance change of Q_A and P680^+, respectively. Each of the 100-200mu s kinetics was disappeared in the presence of an artificial electron donor, Mn^<2+>, which enhances the linear electron flow. The amplitude of each kinetics indicated a similar dependency on redox potential (larger at higher potential, Em=420-470mV), which was nearly equal to the midpoint potential of the high redox potential form of cytochrome b-559 (HPcyt b-559). The amplitude of each 100-200 mu s kinetics and its pH-dependency (larger at higher pH,pKa-6.4) in Tris RC were about twice as much as ones without the non-heme iron. On the basis of these results we concluded the involvement of HPcyt b-559 and the non-heme iron in 100-200 mu s kinetics of the cyclic electron flow.
(2) As models of the donor and acceptor side photoinhibition, we used ferricyanide and Mn^<2+>, respectively to above samples. In the presence of Mn^<2+>,6 beta-carotenes per reaction center complex which has 8 ones were released within 1 minute and the remainder (2 beta-carotenes) were released more slowly. PQ_A were released after the release of about 6 beta-carotenes. We found that these beta-carotenes are closely associated with the cyclic electron flow. These results suggest that beta-carotene acts as a kind of buffer action for excess electric charge in the reaction center of PSII under the photoinhibition.
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