Publication Date:
2011-05-11
Description:
In a previous study, we measured the redox potential of the primary electron acceptor pheophytin (Phe) a of photosystem (PS) II in the chlorophyll d–dominated cyanobacterium Acaryochloris marina and a chlorophyll a–containing cyanobacterium, Synechocystis. We obtained the midpoint redox potential (Em) values of −478 mV for A. marina and −536 mV for Synechocystis. In this study, we measured the redox potentials of the primary electron acceptor quinone molecule (QA), i.e., Em(QA/QA−), of PS II and the energy difference between [P680·Phe a−·QA] and [P680·Phe a·QA−], i.e., ΔGPhQ. The Em(QA/QA−) of A. marina was determined to be +64 mV without the Mn cluster and was estimated to be −66 to −86 mV with a Mn-depletion shift (130–150 mV), as observed with other organisms. The Em(Phe a/Phe a−) in Synechocystis was measured to be −525 mV with the Mn cluster, which is consistent with our previous report. The Mn-depleted downshift of the potential was measured to be approximately −77 mV in Synechocystis, and this value was applied to A. marina (−478 mV); the Em(Phe a/Phe a−) was estimated to be approximately −401 mV. These values gave rise to a ΔGPhQ of −325 mV for A. marina and −383 mV for Synechocystis. In the two cyanobacteria, the energetics in PS II were conserved, even though the potentials of QA− and Phe a− were relatively shifted depending on the special pair, indicating a common strategy for electron transfer in oxygenic photosynthetic organisms.
Print ISSN:
0027-8424
Electronic ISSN:
1091-6490
Topics:
Biology
,
Medicine
,
Natural Sciences in General
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