1987 Fiscal Year Final Research Report Summary
Analysis of spinach photosystem-I reaction-center complex by dissociation and re-association of its components
| Project/Area Number |
61540493
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
植物生理学
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| Research Institution | TEIKYO UNIVERSITY |
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Principal Investigator |
IKEGAMI Isamu Fac.Pharmaceutical Sci., Teikyo Univ., 薬学部, 助教授 (10082322)
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| Project Period (FY) |
1986 – 1987
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| Keywords | Photosynthesis / Phtosystem I / Reaction center / P700 / vitamin K_1 |
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| Research Abstract |
1. Ether treatment of PS-I particle removed all the vitamin K-1 (2.2 mol/P700 in the original particles) as well as most antenna pigments which led a chl-a/P700 ratio to less than 10 in the particle. 2. This preparation showed the A_o^- EPR signal but no A^1 signal even after long illumination at 210K to 230K. 3. Flash-induced absorption changes were studied in this prepartion, where the initial absorption change at 820 nm was followed by a fast decay(t_<1/2>-47 ns at 278K and -82 ns at 10K) which is attributed to the decay of the primary radical pair(P700^+-A^o^-). 4. The A_o^-/A_- spectrum was obtained by the subtraction of the P700^+/P700 pair(P^+/A^-). It includes bleachings centered at 690 and 430 nm, and broad positive bands in the near infra-red and the blue-green. This spectrum is consistent with A_o being chl-a absorbing at 690 nm. 5. A slower phase of the absorption decay is attributed to the P700 triplet dacay, which was formed as a result of the biradical recombination, with a yield of about 30% at 278K and about 75% at 10K. 6. Addition of vitamin K-1 to the particle resulted in a decrease in the amplitude of the fast nanosecond decay and a concomitant increase in the amplitude of a slow phase, indicating an efficient electron transfer from A_0- to vitamin K-1. 7. However, the photoreduction of Fe-S centers(F_X, F_A and F_B ) was still observed even in the absence of vitamin K-1 when we used the continuous illumination as the excitation light, suggesting the by-pass electron flow from A_0 to A_2(X), through which electrons can gradually accumulate on Fe-S centers during prolonded illumination.
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