title: Redox potentials of primary electron acceptor quinone molecule (QA)- and conserved energetics of photosystem II in cyanobacteria with chlorophyll a and chlorophyll d.
abstract: 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 (E(m)) 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 (Q(A)), i.e., E(m)(Q(A)/Q(A)(-)), of PS II and the energy difference between [P680·Phe a(-)·Q(A)] and [P680·Phe a·Q(A)(-)], i.e., ΔG(PhQ). The E(m)(Q(A)/Q(A)(-)) 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 E(m)(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 E(m)(Phe a/Phe a(-)) was estimated to be approximately -401 mV. These values gave rise to a ΔG(PhQ) 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 Q(A)(-) and Phe a(-) were relatively shifted depending on the special pair, indicating a common strategy for electron transfer in oxygenic photosynthetic organisms.
authors.affiliation: Institute of Plant Physiology, Russian Academy of Sciences, Moscow 127276, Russia.
authors.forename: Suleyman I
authors.initials: SI
authors.lastname: Allakhverdiev
authors.forename: Tohru
authors.initials: T
authors.lastname: Tsuchiya
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Watabe
authors.forename: Akane
authors.initials: A
authors.lastname: Kojima
authors.forename: Dmitry A
authors.initials: DA
authors.lastname: Los
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Tomo
authors.forename: Vyacheslav V
authors.initials: VV
authors.lastname: Klimov
authors.forename: Mamoru
authors.initials: M
authors.lastname: Mimuro
mesh_terms: D016227:Benzoquinones / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000378:metabolism*; D004579:Electron Transport; D004734:Energy Metabolism; D010084:Oxidation-Reduction; D010674:Pheophytins / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D018724:Spinacia oleracea / Q000378:metabolism; D046939:Synechocystis / Q000378:metabolism
chemical_list: D016227:Benzoquinones; D010674:Pheophytins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C004532:quinone; C061694:pheophytin a; C107509:chlorophyll d; D000077194:Chlorophyll A