Reduction of pheophytin in the primary light reaction of photosystem II

Klimov, Vyacheslav V.; Klevanik, A. V.; Шувалов, В.А.

doi:10.1016/0014-5793(77)80580-2

Cited by 396 publications

(152 citation statements)

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“…1, where the potential of the working electrode was set at Ϫ350 mV or Ϫ500 mV. The spectral shape and characteristic peaks at 428, 450, 517, and 547 nm are practically the same as those previously reported for PS II complexes (18,(33)(34)(35)(36). The two bleaches at 517 and 547 nm arise from the Qx bands of Phe a, the bleach at 428 nm is the Soret band (18,33), and the 450 nm peak is due to the Phe a Ϫ absorption (33,37).…”

Section: Resultssupporting

confidence: 68%

“…Such a reductive condition was usually achieved by adding sodium dithionite into a sample solution under anaerobic conditions (18,33,34), leading to the solution's equilibrium potential of Ϫ360 to Ϫ480 mV at pH 6-8.…”

Section: Resultsmentioning

confidence: 99%

“…An attempt in this direction was made in 1979 by Klimov et al (11), who had detected Phe a as the primary electron acceptor in PS II membranes from pea (18). They obtained Ϫ610 Ϯ 30 mV as E m (Phe a/Phe a Ϫ ) and, using the P680* Ϫ Phe a energy difference of Ϸ80 meV from delayed fluorescence measurements (19), estimated the E m (P680/P680 ϩ ) value to be ϩ 1,120 Ϯ 50 mV (11).…”

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confidence: 99%

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Spectroelectrochemical determination of the redox potential of pheophytina, the primary electron acceptor in photosystem II

Kato

Sugiura

Oda

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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Thin-layer cell spectroelectrochemistry, featuring rigorous potential control and rapid redox equilibration within the cell, was used to measure the redox potential Em(Phe a/Phe a ؊ ) of pheophytin (Phe) a, the primary electron acceptor in an oxygen-evolving photosystem (PS) II core complex from a thermophilic cyanobacterium Thermosynechococcus elongatus. Interferences from dissolved O 2 and water reductions were minimized by airtight sealing of the sample cell added with dithionite and mercury plating on the gold minigrid working electrode surface, respectively. The result obtained at a physiological pH of 6.5 was E m(Phe a/Phe a ؊ ) ‫؍‬ ؊505 ؎ 6 mV vs. SHE, which is by Ϸ100 mV more positive than the values measured Ϸ30 years ago at nonphysiological pH and widely accepted thereafter in the field of photosynthesis research. Using the P680* ؊ Phe a free energy difference, as estimated from kinetic analyses by previous authors, the present result would locate the E m(P680/P680 ؉ ) value, which is one of the key parameters but still resists direct measurements, at approximately ؉1,210 mV. In view of these pieces of information, a renewed diagram is proposed for the energetics in PS II.charge separation ͉ photosynthesis ͉ spectroelectrochemistry ͉ water oxidation I n the photosynthetic primary process of higher plants, algae, and cyanobacteria, photosystem (PS) I and PS II cooperate in series to convert photon energy into chemical energy through light-induced charge separation and subsequent electron transfers. PS II appears to catalyze water oxidation at a pentanuclear Mn 4 Ca cluster that accumulates oxidizing equivalents (see recent reviews in refs. 1-5). It is generally supposed that the water oxidation is triggered by charge separation between the primary electron donor, P680, and the primary electron acceptor, pheophytin (Phe) a. The initial radical pair P680 ϩ Phe a Ϫ formed by the charge separation, drives forward electron transfer from Phe a Ϫ to the first plastoquinone Q A , and hole transfer from P680 ϩ to the Mn 4 Ca cluster through a redox-active tyrosine residue denoted Y Z , thus preventing charge recombination. Recent X-ray crystallography clarified the arrangement of protein subunits and cofactors in PS II with 2.9-3.7-Å resolution (6-9), visualizing the electron transfer pathway.To date, the nature of P680 remains controversial. Available experimental data and theoretical analyses suggest that P680 is assignable to the pigment cluster of the four chlorophyll a molecules (denoted P D1 , P D2 , Chl D1 , and Chl D2 ) in the PS II reaction center (1, 5). Further uncertainty surrounds the value of the redox potential E m (P680/P680 ϩ ). Although the E m (P680/ P680 ϩ ) value is an essential parameter to draw a whole picture of the PS II energetics, its direct measurement has never been attained (10) because water, present as dominant (solvent) molecules in most sample solutions, is oxidized first heavily and tends to mask the subsequent oxidation of the target entity P680 at a higher potential. The E m ...

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Section: Resultssupporting

confidence: 68%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Spectroelectrochemical determination of the redox potential of pheophytina, the primary electron acceptor in photosystem II

Kato

Sugiura

Oda

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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“…F m is associated with full reduction of Q A and with the trappingincompetent closed RC. Other electron transport intermediates at the acceptor and donor sides of PSII have been proposed as additional functional quenchers like Phe (Phe) (Klimov et al 1977;Vredenberg 2000), reduced forms of the secondary quinone acceptor Q B - (Samson et al 1999;Yaakoubd et al 2002, Schreiber 2002 and Q B 2- (Zhu et al 2005), plastoquinone (PQ) (Vernotte et al 1979), oxidized primary (P 680 + ) (Butler 1972), and secondary donor (Y z + ) (Vredenberg et al 2001) or side products like triplet carotenoids (car T ) (Steffen et al 2001). Their quenching has been discussed in relation to the seeming paradox that the release of fluorescence quenching F v in a single turnover flash (STF) in which all Q A is reduced, is substantially below that measured in multi-turnover light pulses (MTF) (Kramer et al 1995;Samson and Bruce 1996;Kolber et al 1998;Vasilev and Bruce 1998;Samson et al 1999;Koblizek et al 2001;Vredenberg et al 2005).…”

Section: Introductionmentioning

confidence: 99%

On the chlorophyll a fluorescence yield in chloroplasts upon excitation with twin turnover flashes (TTF) and high frequency flash trains

2007

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Chlorophyll fluorescence is routinely taken as a quantifiable measure of the redox state of the primary quinone acceptor Q A of PSII. The variable fluorescence in thylakoids increases in a single turnover flash (STF) from its low dark level F o towards a maximum F m STF when Q A becomes reduced. We found, using twin single turnover flashes (TTFs) that the fluorescence increase induced by the first twin-partner is followed by a 20-30% increase when the second partner is applied within 20-100 ls after the first one. The amplitude of the twin response shows a period-of-four oscillation associated with the 4-step oxidation of water in the Kok cycle (S states) and originates from two different trapped states with a life time of 0.2-0.4 and 2-5 ms, respectively. The oscillation is supplemented with a binary oscillation associated with the two-electron gate mechanism at the PSII acceptor side. The F(t) response in high frequency flash trains (1-4 kHz) shows (i) in the first 3-4 flashes a transient overshoot 20-30% above the F m STF = 3*F o level reached in the 1st flash with a partial decline towards a dip D in the next 2-3 ms, independent of the flash frequency, and (ii) a frequency independent rise to F m = 5*F o in the 3-60 ms time range. The initial overshoot is interpreted to be due to electron trapping in the S 0 fraction with Q B -nonreducing centers and the dip to the subsequent recovery accompanying the reoxidation of the double reduced acceptor pair in these RCs after trapping. The rise after the overshoot is, in agreement with earlier findings, interpreted to indicate a photo-electrochemical control of the chlorophyll fluorescence yield of PSII. It is anticipated that the double exciton and electron trapping property of PSII is advantageous for the plant. It serves to alleviate the depression of electron transport in single reduced Q B -nonreducing RCs, associated with electrochemically coupled proton transport, by an increased electron trapping efficiency in these centers.Keywords Chlorophyll a Á Fluorescence quenching Á Q B -nonreducing center Á Single turnover excitation Á Twin turnover excitation Á Three state trapping mechanism (TSTM)

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“…DPC was used as an artificial electron donor at 0.5 mM. Photoreduction of pheophytin was measured with a Hitachi 356 spectrophotometer in the dual-wavelength mode (450 minus 500 nm) in 50 mM Tris-HCI (pH 7.5) in the presence of 5/zM methyl viologen, 2-5 mg/ml sodium dithionite and 30% glycerol [15]. The sample (5-10/~g Chl/ml) was excited by strong actinic light passed through a red cut-off filter (VR-66, Toshiba) with a crossillumination system.…”

Section: Methodsmentioning

confidence: 99%

Isolation of photosystem II reaction center complex by affinity chromatography with the peripheral 33‐kDa polypeptide as ligand

Isogai

Yamamoto

et al. 1987

FEBS Letters

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We report a procedure for one-step isolation of the PS II reaction center complex from PS II particles by affinity chromatography with the peripheral 33-kDa polypeptide as ligand. The CaClz-washed PS II particles prepared from spinach chloroplasts were solubilized with n-octyl-fl-D-glucopyranoside and subjected to affinity chromatography. The purified complex consisted of polypeptides with apparent molecular masses of 47, 43, 32, 30 and 8 kDa.

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Reduction of pheophytin in the primary light reaction of photosystem II

Cited by 396 publications

References 9 publications

Spectroelectrochemical determination of the redox potential of pheophytina, the primary electron acceptor in photosystem II

Spectroelectrochemical determination of the redox potential of pheophytina, the primary electron acceptor in photosystem II

On the chlorophyll a fluorescence yield in chloroplasts upon excitation with twin turnover flashes (TTF) and high frequency flash trains

Isolation of photosystem II reaction center complex by affinity chromatography with the peripheral 33‐kDa polypeptide as ligand

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