Redox potentials of primary electron acceptor quinone molecule (QA)⁻ and conserved energetics of photosystem II in cyanobacteria with chlorophyll a and chlorophyll d

• Published in: Proceedings of the National Academy of Sciences - PNAS 2011-05, Vol.108 (19), p.8054-8058
• Main Authors: Allakhverdiev, Suleyman I, Tsuchiya, Tohru, Watabe, Kazuyuki, Kojima, Akane, Los, Dmitry A, Tomo, Tatsuya, Klimov, Vyacheslav V, Mimuro, Mamoru
• Format: Article
• Language: English
• Subjects: Acaryochloris marina; autotrophs; Bacteria; Benzoquinones - metabolism; Bicarbonates; Biochemistry; Bioenergetics; Biological Sciences; Chlorophyll; Chlorophyll - metabolism; Chlorophylls; Cyanobacteria; Cyanobacteria - metabolism; Electron transfer; Electron Transport; Electrons; Energy; Energy Metabolism; Manganese; Marinas; Oxidation-Reduction; Pheophytins - metabolism; Photosynthesis; Photosystem II; Photosystem II Protein Complex - metabolism; Quinone; Redox potential; Spinach; Spinacia oleracea - metabolism; Studies; Synechocystis; Synechocystis - metabolism; Titration
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1100173108

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.