1992 Fiscal Year Final Research Report Summary
Assembly of the Mn cluster in the water-oxidizing complex in the photosynthetic membranes.
| Project/Area Number |
03804054
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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 | Fukuoka Women s University |
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Principal Investigator |
TAMURA Noriaki Fukuoka Women s University, Dept. of Biology Associate Professor, 家政学部, 助教授 (70207249)
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| Co-Investigator(Kenkyū-buntansha) |
INOUE Hiroshi Toyama University, Dept. of Biology Professor, 理学部, 教授 (50109097)
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| Project Period (FY) |
1991 – 1992
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| Keywords | Photo synthesis / Oxygen evolution / Photosystem / Manganese / Water oxidation |
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| Research Abstract |
The results that we have obtained for two years are as follows:
1. We succeeded in photo activation of the water-oxidizing complex (WOC) of the PSII core complex, which is mainly constituted of 47kDa/43kDa/D1/D2/Cyt b559 butis depleted of light-harvesting chlorophyll proteins. Characteristics of this photo activation are : (1) a shift of optimum pH more acidic than for PSII membranes, (2) Destabilization of the intermediate generated during photo activation, and (3) low affinity of Mn^<2+> and Ca^<2+> to their respective binding sites in WOC.
2. The effect of 3-(3.4-dichlorophenyl)-1, 1-dimethylurea (DCMU) on the oxidizing side have been studied with PSII membranes. The inhibition constant for DCMU in the diphenylcarbazide-supported silicomolybdate-photoreduction was 10muM. The extent of inhibition was attenuated by modification of the PSII oxidizing side by the presence of functional Mn, by photoinhibition and by chemical modification of histidine residues and carboxyl groups. Our results indicate that DCMU binds to the PSII oxidizing side in addition to the common binding site.
3. The capability of photo activation was decreased in NH_2OH-treated wheat leaves subjected to continuous weak light. However, O_2 evolution activity was restored by the subsequent light. This light-dependent recovery from photoinhibition required the synthesis of the D1/D2 proteins, but not Cyt b559/47kDa protein. On the contrary, all of chloroplast-encoded PSII proteins were synthesized during the light illumination in untreated leaves.
4. The capability of photo activation was abolished by the chemical modification of acidic amino acid residues in PSII membranes depleted of WOC, while the PSII electron transfer bypassing WOC was not affected. The modification, which is specific for photoligation of Mn^<2+>, occurred on at least D1 protein. These results indicate that Mn^<3+> photooxidized is ligated to the acidic amino acid residues of the D1 protein.
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[Publications] Tamura, N., Tanaka, T., Wakamatsu, K., Inoue, H. and Wad a, K.: "Possible role of carboxyl groups in photo-activation of the apo-water-oxidizing complex." Research in Photosynthesis (Murata, N.ed.) Vol.II pp. 405-408 Kluwer Academic Publishers, The Netherlands. (1992)
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