A change in the midpoint potential of the quinone QA in Photosystem II associated with photoactivation of oxygen evolution

Johnson, Giles N.; Rutherford, A. William; Krieger, Anja

doi:10.1016/0005-2728(95)00003-2

Cited by 184 publications

(207 citation statements)

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“…Chlorophyll triplets are relatively long-lived and very reactive with O 2 to generate 1 O 2 , a very toxic species. This concept of redox tuning controlling the competition between two main charge recombination routes in PSII (13) has dominated much of the subsequent thinking concerning photoinhibition and redox-based protective mechanisms (18)(19)(20).…”

Section: Significancementioning

confidence: 99%

“…In a parallel study, Johnson et al (13) showed that the high and low potential forms of Q A had clear physiological relevance. PSII is assembled as a functional photochemical reaction center lacking the Mn 4 CaO 5 cluster and consequently, unable to split water.…”

mentioning

confidence: 99%

“…The current detailed thermodynamic picture of PSII redox chemistry is based on estimates of energy differences between the electron transfer components, but these estimates rely on measurements of redox potentials to fix absolute values (1)(2)(3) A , differing by ∼150 mV, depending on the nature of the PSII (12)(13)(14). The fully active enzyme showed an E m value that was ∼150 mV lower than that in PSII lacking the Mn 4 CaO 5 cluster.…”

mentioning

confidence: 99%

“…The fully active enzyme showed an E m value that was ∼150 mV lower than that in PSII lacking the Mn 4 CaO 5 cluster. This shift was, in fact, due to the binding (or absence thereof) of the Ca 2+ ion involved in water splitting, but because the Mn cluster provides the Ca binding site, the potential is indirectly determined by the presence of Mn cluster (12)(13)(14). Given the high valence state on the Mn cluster even in the lowest redox state of the water splitting cycle (15), it is not surprising that the use of chemical mediators, the role of which is to equilibrate the external redox potential with the cofactors, can lead to the reduction and consequent loss of the Mn cluster.…”

mentioning

confidence: 99%

“…It then undergoes a light-driven oxidative process by which the cluster is assembled (16), so-called photoactivation. The downshift in the redox potential of Q A =Q −• A occurs during photoactivation (13). A rationale was given for this process, with two competing pathways for the decay P +• Q −• A by charge…”

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confidence: 99%

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Bicarbonate-induced redox tuning in Photosystem II for regulation and protection

Brinkert

Causmaecker

Krieger‐Liszkay

et al. 2016

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

120

173

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The midpoint potential (E m ) of Q A =Q −• A , the one-electron acceptor quinone of Photosystem II (PSII), provides the thermodynamic reference for calibrating PSII bioenergetics. Uncertainty exists in the literature, with two values differing by ∼80 mV. Here, we have resolved this discrepancy by using spectroelectrochemistry on plant PSII-enriched membranes. Removal of bicarbonate (HCO 3 − ) shifts the E m from ∼−145 mV to −70 mV. The higher values reported earlier are attributed to the loss of HCO 3 − during the titrations (pH 6.5, stirred under argon gassing). P hotosystem II (PSII), the water/plastoquinone photooxidoreductase, is at the heart of the major energy cycle that powers the biosphere. Chlorophyll-based photochemistry drives charge separation followed by electron transfer reactions that result in the reduction of quinone on one side of the thylakoid membrane ( Fig. 1) and the oxidation of water on the other. The photochemistry is intrinsically a one-photon/one-electron process, but the quinone reduction and water oxidation are two-and fourelectron processes, respectively. As a result, both processes involve the accumulation of intermediates that are stabilized by the protein and by coupling to protonation reactions (1-3).The electron acceptor side of PSII contains a nonheme ferrous iron (Fe 2+ ) that is flanked by the two quinones, Q A and Q B (Fig. 1) (reviewed in refs. 3 and 4). The Fe 2+ is coordinated by four histidine residues, two from D1 and two from D2, and a bicarbonate ion (HCO 3 − ) that provides a bidentate ligand (3-5). The HCO 3 − is thought to play a role in the Q B protonation pathway (reviewed in refs. 3-5). Recent EPR (6) and computation chemistry studies (7) based on the highest-resolution X-ray crystallographic model (8) implicated HCO 3 − in the second of two protonation steps that are associated with Q B reduction. Measurements of the dissociation constant of HCO 3 − (K d = 40-80 μM), compared with estimates of the HCO 3 − concentration in the stroma (reviewed in ref. 9), led to the assumption that HCO 3 − remains bound under physiological conditions (10). Recently, however, it was reported that the HCO 3 − bound to PSII in Chlamydomonas can be displaced by acetate when present in the culture medium (11).The redox potential of Q A has been the subject of research for decades (12). The current detailed thermodynamic picture of PSII redox chemistry is based on estimates of energy differences between the electron transfer components, but these estimates A , differing by ∼150 mV, depending on the nature of the PSII (12-14). The fully active enzyme showed an E m value that was ∼150 mV lower than that in PSII lacking the Mn 4 CaO 5 cluster. This shift was, in fact, due to the binding (or absence thereof) of the Ca 2+ ion involved in water splitting, but because the Mn cluster provides the Ca binding site, the potential is indirectly determined by the presence of Mn cluster (12)(13)(14). Given the high valence state on the Mn cluster even in the lowest redox state of the water splitti...

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Section: Significancementioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Bicarbonate-induced redox tuning in Photosystem II for regulation and protection

Brinkert

Causmaecker

Krieger‐Liszkay

et al. 2016

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

120

173

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Photosynthetic Regulatory Mechanisms for Efficiency and Prevention of Photo‐Oxidative Stress

Roach

Krieger‐Liszkay

2019

Annual Plant Reviews Online

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Regulatory mechanisms of photosynthesis affecting light capture, the efficiency of electron transport, and the distribution between linear and alternative electron transport routes are needed to balance energy input with metabolic demands. Rapid fluctuations in light intensity lead transiently to absorption of excess light energy, requiring immediate regulation, whereas adverse environmental conditions over longer‐term require acclimation responses. In either case, excitation of photosynthetic pigments beyond metabolic demand and unpoised electron transfer reactions can lead to the generation of reactive oxygen species (ROS). On the one hand, ROS damage the photosynthetic machinery and other macro‐molecules, such as thylakoid membranes, contributing to photo‐oxidative stress. On the other hand, ROS are needed for acclimation responses since they affect the expression level of responsive genes, as well as exert direct and indirect effects on redox‐regulated processes in the chloroplast. In this article, we introduce the photosynthetic complexes, step‐by‐step and focus on the regulatory mechanisms required to enable photosynthetic efficiency and control levels of ROS production. Finally, we shortly describe the roles of chloroplast‐derived ROS in the short‐term modulation of photosynthesis and the longer‐term acclimation to light stress. Differences in regulatory mechanisms amongst the diversity of Viridiplantae (i.e. green algae to plants) are described.

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A thermoluminescence study of the effects of nitrite on photosystem II in spinach thylakoids

2006

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The site of action of nitrite on PS II was investigated by measuring the TL profile of nitrite-treated spinach thylakoid membranes. Three bands were observed in control, which were identified as the Q band (7 degrees C), the B band (24 degrees C) and the C band (57 degrees C). In the presence of 20 mmol/L nitrite, the intensity of the Q band decreased, the B band upshifted to 46 degrees C but the C band disappeared. The suppression of the Q band and the upshift of the B band suggested that nitrite caused inhibition at the water oxidizing complex. The effects of nitrite also remained the same in the presence of chloride. In case of ion-sufficient thylakoid membranes, nitrite decreased the Q band peak intensity and caused an upshift in the B band peak temperature. Nitrite showed similar effects in the presence of DCMU. This suggested that the site of action of nitrite is not at the acceptor side but at the donor side of PS II. The inhibition shown by nitrite has been found to be specific for nitrite anion. No other anions such as formate, fluoride or nitrate, were effective.

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A change in the midpoint potential of the quinone QA in Photosystem II associated with photoactivation of oxygen evolution

Cited by 184 publications

References 40 publications

Bicarbonate-induced redox tuning in Photosystem II for regulation and protection

Bicarbonate-induced redox tuning in Photosystem II for regulation and protection

Photosynthetic Regulatory Mechanisms for Efficiency and Prevention of Photo‐Oxidative Stress

A thermoluminescence study of the effects of nitrite on photosystem II in spinach thylakoids

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