The PsbQ′ protein affects the redox potential of the QA in photosystem II
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Red alga contains four extrinsic proteins in photosystem II (PSII), which are PsbO, PsbV, PsbU, and PsbQ′. Except for the PsbQ′, the composition is the same in cyanobacterial PSII. Reconstitution analysis of cyanobacterial PSII has shown that oxygen-evolving activity does not depend on the presence of PsbQ′. Recently, the structure of red algal PSII was elucidated. However, the role of PsbQ′ remains unknown. In this study, the function of the acceptor side of PSII was analyzed in PsbQ′-reconstituted PSII by redox titration of QA and thermoluminescence. The redox potential of QA was positively shifted when PsbQ′ was attached to the PSII. The positive shift of QA is thought to cause a decrease in the amount of triplet chlorophyll in PSII. On the basis of these results, we propose that PsbQ′ has a photoprotective function when irradiated with strong light.
Additional key wordsdiversity evolution photoinhibition photosynthesis
chlorophyll protein 43 kDa
chlorophyll protein 47 kDa
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