Modulation of Flash-Induced Photosystem II Fluorescence by Events Occurring at the Water Oxidizing Complex
The mechanism of flash-induced changes with a periodicity of four in photosystem II (PSII) fluorescence was investigated with the aim of further using fluorescence measurements as an approach to studying the structural and functional organization of the water-oxidizing complex (WOC). The decay of th...
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Published in | Biochemistry (Easton) Vol. 38; no. 33; pp. 10632 - 10641 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
17.08.1999
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Subjects | |
Online Access | Get full text |
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Summary: | The mechanism of flash-induced changes with a periodicity of four in photosystem II (PSII) fluorescence was investigated with the aim of further using fluorescence measurements as an approach to studying the structural and functional organization of the water-oxidizing complex (WOC). The decay of the flash-induced high fluorescence state of PSII was measured with pulse amplitude modulated fluorometry in thylakoids and PSII enriched membrane fragments. Calculated QA - decay was well described by three exponential decay components, reflecting QA - reoxidation with halftimes of 450 and 860 μs, 2 and 7.6 ms, and 111 and 135 ms in thylakoids and PSII membranes, respectively. The effect of modification of the PSII donor side by changing pH or by removal of the extrinsic 17 and 24 kDa proteins on period four oscillations in both maximum fluorescence yield and the relative contribution of QA - reoxidation reactions was compared to flash-induced oxygen yield. The four-step oxidation of the manganese cluster of the WOC was found to be necessary but not sufficient to produce modulation of PSII fluorescence. The capacity of the WOC to generate molecular oxygen was also required to observe a period four in the fluorescence; however, direct quenching by oxygen was not responsible for the modulation. Potential mechanisms responsible for the periodicity of four in both maximum fluorescence yield pattern and flash-dependent changes in proportion of centers with different QA - reoxidation rates are discussed with respect to intrinsic deprotonation events occurring at the WOC. |
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Bibliography: | istex:F89F683195B5D86F36BBDF168FB81CD8277B0276 ark:/67375/TPS-L4FPVGLS-J This work was supported by operating and equipment grants from the Natural Science and Engineering Research Council of Canada (NSERC) to D.B. and by a NATO Science Postdoctoral Fellowship from NSERC to I.P. ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0006-2960 1520-4995 |
DOI: | 10.1021/bi990518j |