The influence of the quinone-iron electron acceptor complex on the reaction centre photochemistry of Photosystem II

Mieghem, F.J.E. van; Nitschke, Wolfgang; Mathis, Paul; Rutherford, A. William

doi:10.1016/s0005-2728(89)80073-8

Cited by 144 publications

(117 citation statements)

References 31 publications

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“…It has been suggested previously that HCO-could be involved in protonation of PSII quinone acceptors (28,29). Protonation of reduced QA improves the yield of charge separation owing to the removal of the electrostatic repulsion between Pheo-and QA (30)(31)(32) (32). A better recovery of variable fluorescence and variable thermal dissipation is obtained when Co is added together with Mn and HCO3 in the reconstitution medium (Fig.…”

Section: Methodsmentioning

confidence: 82%

Variable thermal emission and chlorophyll fluorescence in photosystem II particles.

Allakhverdiev

Klimov

Carpentier

1994

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

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In photosynthetic systems, the absorbed light energy is used to generate electron transport or it is lost in the form of fluorescence and thermal emission. While fluorescence can be readily measured, the detection of thermal deactivation processes can be achieved by the photoacoustic technique. In that case, the pressure wave generated by the thermal deactivations in a sample irradiated with modulated light is detected by a sensitive microphone. The relationships between the yield of fluorescence and thermal emissions measured simultaneously were analyzed by using a spinach photosystem II (PSH)-enriched preparation. It is shown that the quenching of fluo- In the photosynthetic apparatus, the absorbed light energy is either used to generate electron transport that is initiated by charge separation at the level of photosystems I and II (PSI and PSII), or the energy is lost through fluorescence and thermal emission. Fluorescence can be readily measured, but photoacoustic (PA) spectroscopy has been advantageously used to study the thermal deactivation processes in photosynthetic materials (1). In that case, a solid or semisolid sample is irradiated with modulated light in a closed cell. The thermal deactivations generate a periodic heat flow in the The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. surrounding gas medium that produces a pressure wave transduced into an electric signal by a sensitive microphone. Most usefully, the difference between the thermal emission yields ofactive and inactive samples allows the determination of the photochemical energy-storage yield (2). In most studies, the inactive sample with closed reaction centers was obtained by superimposition of a nonmodulated background light of saturating intensity on the low-intensity modulated measuring beam (3-6). The energy-storage yield has been correlated with the electron transport status (7,8), and it was suggested that electron transfer from water to the plastoquinone (PQ) pool was responsible for the stored energy (8-10).Similarly, part of the fluorescence emission (the so-called variable fluorescence) is closely related to the redox state of the secondary acceptors QA and QB in PSII and therefore is greatly influenced by the electron transport status (11). Thus, a strong interdependence between the yield of energy storage and the yield of variable fluorescence can be suggested (10). The correlation between chlorophyll (Chl) fluorescence and the PA signal has been studied in intact leaves (12, 13). However, the interpretations were complicated by the participation of PSI in the thermal signal and by a photobaric contribution due to oxygen evolution.A PSII submembrane fraction depleted of PSI should constitute the simplest model to study the relationship between variable fluorescence emission and thermal energy storage. The thermal emission behavior of such preparations has been...

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Section: Methodsmentioning

confidence: 82%

Variable thermal emission and chlorophyll fluorescence in photosystem II particles.

Allakhverdiev

Klimov

Carpentier

1994

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

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“…It could be argued based upon the suggestions in [12,13], that the double reduction and protonation of QA in itself lead to a release of this species from the reaction centre in the same way as QBHl is released from the Dl-protein during normal electron transport. Alternatively, the double reduction of QA or some other light-induced damage may induce a conformational change in the DZprotein that lowers the binding affinity of QA.…”

Section: Discussionmentioning

confidence: 99%

Reduced content of the quinone acceptor Q_A in photosystem II complexes isolated from thylakoid membranes after prolonged photoinhibition under anaerobic conditions

et al. 1993

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The plastoquinone content of photosystem II complexes isolated from spinach photosystem II-enriched membranes subjected to strong photoinhibitory illumination under anaerobic conditions was determined by HPLC. A pronounced decrease of the plastoquinone content was found in the photoinactivated complexes. These results corroborate earlier models in which photoinhibitory illumination is suggested to eventually lead to release of doubly reduced and protonated QA from its site on the DZ-protein.

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“…Since Pheo-is a strong reductant it can reduce QA (26). The doubly reduced 04-is proposed to be protonated and then to debind from PSII (21,22,27), leading to removal of the D1 polypeptide.…”

Section: Discussionmentioning

confidence: 99%

“…3. The redox couple QV/Q2-is not a likely candidate because it has a low midpoint potential (E, < -350 mV) (27), nor is protonation of one of the reduced states of QA, because the component controlling the rate of photoinhibition is nearly pH independent (Fig. 5).…”

Section: Discussionmentioning

confidence: 99%

Redox state of a one-electron component controls the rate of photoinhibition of photosystem II.

Nedbal

Samson

Whitmarsh

1992

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

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Photosystem H reaction centers in plants, algae, and cyanobacteria are susceptible to damage by excess light that irreversibly impairs activity and eventually results in the proteolytic degradation of at least one of the core proteins. Oxygenic photosynthetic organisms are vulnerable to damage by a number of environmental factors, including visible light, UV-B radiation, heat, cold, drought, and atmospheric pollutants (1). In some cases, the site of damage is the photosystem II (PSII) reaction center, a membrane-bound, multisubunit complex that catalyzes the oxidation of water and the reduction of plastoquinone (2). The PSII reaction center provides approximately half the energy used for biomass production in plants and is responsible for the release of molecular oxygen into the atmosphere. The reaction center core is composed of the a and f8 subunits of cytochrome b-559 (Cyt b559) and the two proteins, D1 and D2, that bind the redox components known to be required for electron transfer from the water-oxidizing manganese cluster to plastoquinone. These include the primary donor (P680), the secondary donor (Yz), the primary acceptor pheophytin (Pheo), and the primary and secondary plastoquinone acceptors (QA and QB).Exposure of PSII to supersaturating levels of visible light causes the loss of water oxidation (3) and eventually leads to removal and degradation of the D1 polypeptide (4). There is disagreement concerning the early events that lead to photoinhibition of the reaction center (reviewed in ref. 5). Using thylakoid membranes as model systems, some experiments show that the initial site of damage is on the oxidizing side of PSII, whereas other experiments, often done under different conditions, show that the primary site of damage is on the reducing side of PSII. These results form the basis for two models of photoinhibition: those that focus on damage done by the highly oxidizing cation radicals and those that focus on damage done by the highly reducing anion radicals.This study was initiated to investigate the molecular mechanism of PSII photoinhibition and protective reactions. Potentiometric titrations reveal that a one-electron redox component plays a critical role in the process. The rate of PSII damage is dramatically increased when the component is reduced. We suggest that the redox component is the lowpotential form of Cyt b559 (Cyt b559LP), which protects the reaction center from photoinhibition by providing an alternative electron pathway that can oxidize the damaging radical state P680/Pheo-/QA-MATERIALS AND METHODS Membrane Isolation. Spinach leaves (Spinacia oleracea) were either harvested from plants grown hydroponically (6) or bought from a local market. Thylakoid membranes were isolated from leaves as described (7) and stored on ice at a chlorophyll concentration of 1-2 mM in medium containing 5 mM Hepes-NaOH (pH 7.5), 200 mM sorbitol, 2 mM MgCl2, and fatty acid-free bovine serum albumin (0.5 mg/ml). The membranes were used for experiments within 7 h ofisolation. Chlorophyll conce...

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The influence of the quinone-iron electron acceptor complex on the reaction centre photochemistry of Photosystem II

Cited by 144 publications

References 31 publications

Variable thermal emission and chlorophyll fluorescence in photosystem II particles.

Variable thermal emission and chlorophyll fluorescence in photosystem II particles.

Reduced content of the quinone acceptor Q_A in photosystem II complexes isolated from thylakoid membranes after prolonged photoinhibition under anaerobic conditions

Redox state of a one-electron component controls the rate of photoinhibition of photosystem II.

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The influence of the quinone-iron electron acceptor complex on the reaction centre photochemistry of Photosystem II

Cited by 144 publications

References 31 publications

Variable thermal emission and chlorophyll fluorescence in photosystem II particles.

Variable thermal emission and chlorophyll fluorescence in photosystem II particles.

Reduced content of the quinone acceptor QA in photosystem II complexes isolated from thylakoid membranes after prolonged photoinhibition under anaerobic conditions

Redox state of a one-electron component controls the rate of photoinhibition of photosystem II.

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Reduced content of the quinone acceptor Q_A in photosystem II complexes isolated from thylakoid membranes after prolonged photoinhibition under anaerobic conditions