Charge accumulation at the reducing side of system 2 of photosynthesis

Velthuys, B.R.; Amesz, J.

doi:10.1016/0005-2728(74)90165-0

Cited by 343 publications

(100 citation statements)

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“…The rate of reduction of Q B is faster than the rate of reduction of Q B Ϫ (see ref. 6 and references therein), which gives rise to a characteristic period-2 oscillation in kinetics originating on the PSII acceptor side (7).…”

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confidence: 99%

Time-resolved vibrational spectroscopy detects protein-based intermediates in the photosynthetic oxygen-evolving cycle

Barry

Cooper²,

Riso³

et al. 2006

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

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Photosynthetic oxygen production by photosystem II (PSII) is responsible for the maintenance of aerobic life on earth. The production of oxygen occurs at the PSII oxygen-evolving complex (OEC), which contains a tetranuclear manganese (Mn) cluster. Photo-induced electron transfer events in the reaction center lead to the accumulation of oxidizing equivalents on the OEC. Four sequential photooxidation reactions are required for oxygen production. The oxidizing complex cycles among five oxidation states, called the S n states, where n refers to the number of oxidizing equivalents stored. Oxygen release occurs during the S 3-to-S0 transition from an unstable intermediate, known as the S4 state. In this report, we present data providing evidence for the production of an intermediate during each S state transition. These proteinderived intermediates are produced on the microsecond to millisecond time scale and are detected by time-resolved vibrational spectroscopy on the microsecond time scale. Our results suggest that a protein-derived conformational change or proton transfer reaction precedes Mn redox reactions during the S 2-to-S3 and S 3-to-S0 transitions.manganese cluster ͉ photosynthesis ͉ photosystem II ͉ time-resolved IR ͉ water oxidation T ime-resolved vibrational spectroscopy can detect chemical intermediates formed during enzymatic catalysis. Advantages include the technique's exquisite structural sensitivity and its high temporal resolution. Recent advances in methodology and interpretation have produced insights into the catalytic mechanism in several biological systems (for examples, see refs. 1-4).In this paper, we report the use of time-resolved IR spectroscopy to investigate the mechanism of photosynthetic water oxidation. Photosystem II (PSII) catalyzes the oxidation of water and the reduction of bound plastoquinone. Photoexcitation of PSII leads to the oxidation of the chlorophyll donor, P 680 , and the sequential reduction of a pheophytin (Fig. 1A, reaction 1) and a plastoquinone, Q A ( Fig. 1 A, reaction 2), in picoseconds. Q A reduces Q B to generate a semiquinone radical, Q B Ϫ , on the microsecond time scale (Fig. 1 A, reaction 3 ) (reviewed in ref. 5).A second photoexcitation leads to the reduction and protonation of Q B Ϫ to form the quinol Q B H 2 . The rate of reduction of Q B is faster than the rate of reduction of Q B Ϫ (see ref. 6 and references therein), which gives rise to a characteristic period-2 oscillation in kinetics originating on the PSII acceptor side (7).The primary chlorophyll donor, P 680 , oxidizes a tyrosine, Y Z (Y161 in the D1 subunit), on the nanosecond to microsecond time scale (Fig. 1 A, reaction 4). In turn, tyrosine Y Z ⅐ oxidizes the oxygen-evolving complex (OEC) on every flash (Fig. 1 A, reaction 5) (8). Four sequential photooxidation reactions are required for oxygen production, and the oxidizing complex cycles among five oxidation states, called the S n states, where n refers to the number of oxidizing equivalents stored (9). The rate of OEC oxidation slows as o...

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confidence: 99%

Time-resolved vibrational spectroscopy detects protein-based intermediates in the photosynthetic oxygen-evolving cycle

Barry

Cooper²,

Riso³

et al. 2006

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

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“…The 'two-electron gate' intermediate QB connects the one-electron carrier QA with the two-electron carrier plastoquinone pool [ 1,2]. Photosystem II inhibitors, some of which are used as efficient herbicides, compete with plastoquinone for binding at the secondary quinone acceptor site (QB site) to the Dl-protein [3].…”

Section: Introductionmentioning

confidence: 99%

Anthraquinone inhibitors of photosystem II electron transport

1988

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Various substituted 9,10-anthraquinones were tested for their inhibitory activity on photosystem II electron transport. Maximal inhibitory activity was achieved if the positions adjacent to one of the quinone carbonyl groups were unsubstituted or substituted by hydroxyl groups only. The best anthraquinone type inhibitor found so far was 2,3,4-trichloro-lhydroxy-anthraquinone with a pl,, value of 7.75. This is well comparable to the most powerful known photosystem II

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“…It appears that Q1 and QH are the same acceptor located on a side different from that of Q2 and QL" QB, the secondary quinone acceptor of PSII (Figs. I-3), is thought to function in a two-electron gating mechanism [5,83].…”

Section: Introduction !mentioning

confidence: 99%

Electron transfer through photosystem II acceptors: Interaction with anions

Govindjee

Eaton‐Rye

1986

Photosynth Res

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We present an overview of anionic interactions with the oxidationreduction reactions of photosystem II (PSII) acceptors.In section I, a framework is lald for the electron ~cceptor side of PSII:the overview begins with a current scheme of the electron transport pathway and of the localization of components in the thylakoid membrane, which is followed by a brief description of the electron acceptor Q or QA and the various heterogeneities associated with it. In section 2, we review briefly the nature of the active species of the bicarbonate (HC03) effect, the location of the site of action of HCO], and its Pelatlonship to interactions with other anions.In section 3,-we review data on the anion effects on the reoxldation of QA and on the various reactions involved in the twoelectron gate mechanism of PSII,~and prOvldela:hypothesis as to the action of HCO 3 on the protonation reactions.New data ~btalned by one of us (G) in collaboration with J.J.S. van Rensen, J.F.H Sne! and W. Tonk for HCO3-depleted thylakolds, demonstrating the abolition iof the binary oscill~-tlons contained within the periodicity of 4 observed for proton release, are also reviewed.In section 4, we comment on t~e measured binding constant of HCO3 at the anion binding site. And, in section 5, we review our current concept of the mechanism of the HCO3 effect on the electron accepter side of PSII, and_comment on the possible physiological roles for HCO 3.Measurements of HCOg reverslble anionle inhlbltlon in intact cells of ~ green alga Soenedesmus-are also reviewed.

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Charge accumulation at the reducing side of system 2 of photosynthesis

Cited by 343 publications

References 23 publications

Time-resolved vibrational spectroscopy detects protein-based intermediates in the photosynthetic oxygen-evolving cycle

Time-resolved vibrational spectroscopy detects protein-based intermediates in the photosynthetic oxygen-evolving cycle

Anthraquinone inhibitors of photosystem II electron transport

Electron transfer through photosystem II acceptors: Interaction with anions

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