Evidence for two tightly bound iron‐quinones in the electron acceptor complex of photosystem II

Evans, M.C.W.; Ford, Robert C.

doi:10.1016/0014-5793(86)80179-x

Cited by 15 publications

(3 citation statements)

References 17 publications

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“…With our high overall concentrations we assume this still to be the case. On the acceptor side acetate may deplete bicarbonate and thus retard the electron flow from QA to QB and to the plastoquinone pool [21,22]. Thus the electron flow is disturbed on either side of the reaction center forcing electrons into a cyclic path involving Ps+8,-, QA recombination after light excitation, while in the presence of an external lipophilic donor a slow forward reaction can be observed.…”

Section: Discussionmentioning

confidence: 99%

Time resolved EPR on photosystem II particles after irreversible and reversible inhibition of water cleavage with high concentrations of acetate

et al. 1988

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Electron transfer in irreversibly acetate-inhibited PS II preparations from Synechococcus is investigated with EPR. A 1.4 mT wide EPR line with a decay rate consistent with the P,& QA back reaction is tentatively assigned to be a broadened P,',, spectrum. With reversible inhibition of water cleavage by the ADRY reagent FCCP added with acetate electron transfer is studied as well. Under these conditions the spectrum of the immediate donor to P,',, is the same as the spectrum of Z+ in systems with irreversibly inhibited water cleavage (signal II fast) and the same as that of D+ (signal II slow).The consequences are discussed.

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Section: Discussionmentioning

confidence: 99%

Time resolved EPR on photosystem II particles after irreversible and reversible inhibition of water cleavage with high concentrations of acetate

et al. 1988

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“…The possibility that this difference can be due to differential accessibility of QA has not yet been disproven; an interconvertible heterogeneity of QA-Fe z+ has been shown to exist (Rutherford and Zimmermann 1984). Evans and Ford (1986) suggest the existence of two tightly bound iron quinones in the PS II acceptor complex. It is generally believed that QH is the form that is in the main chain, and QL is not (see e.g., Diner and Delosme 1983); QL is not electrogenic.…”

Section: The Q L and Q Hmentioning

confidence: 99%

Photosystem II heterogeneity: the acceptor side

Govindjee

1990

Photosynth Res

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It is well known that two photosystems, I and II, are needed to transfer electrons from H2O to NADP(+) in oxygenic photosynthesis. Each photosystem consists of several components: (a) the light-harvesting antenna (L-HA) system, (b) the reaction center (RC) complex, and (c) the polypeptides and other co-factors involved in electron and proton transport. First, we present a mini review on the heterogeneity which has been identified with the electron acceptor side of Photosystem II (PS II) including (a) L-HA system: the PS IIα and PS IIβ units, (b) RC complex containing electron acceptor Q1 or Q2; and (c) electron acceptor complex: QA (having two different redox potentials QL and QH) and QB (QB-type; Q'B type; and non-QB type); additional components such as iron (Q-400), U (Em,7=-450 mV) and Q-318 (or Aq) are also mentioned. Furthermore, we summarize the current ideas on the so-called inactive (those that transfer electrons to the plastoquinone pool rather slowly) and active reaction centers. Second, we discuss the bearing of the first section on the ratio of the PS II reaction center (RC-II) and the PS I reaction center (RC-I). Third, we review recent results that relate the inactive and active RC-II, obtained by the use of quinones DMQ and DCBQ, with the fluorescence transient at room temperature and in heated spinach and soybean thylakoids. These data show that inactive RC-II can be easily monitored by the OID phase of fluorescence transient and that heating converts active into inactive centers.

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“…Bicarbonate binding may also influence the redox properties of QA. Only the redox potential characteristics of the g = 1.8 ESR signal have been measured and some measurements have required the interpretation that there is an electron carrier in addition to QA and Qa [25,26]. Redox titrations of QA under conditions where pH, bound bicarbonate and bound QB are controlled are now needed.…”

Section: Discussionmentioning

confidence: 99%

Bicarbonate binding and the properties of photosystem II electron acceptors

et al. 1988

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We have investigated the quinone-binding region of PS II using exchange reactions to replace key components. Bicarbonate was replaced by formate and Qs by exogenous quinones or herbicide. The effects of these changes were monitored using the ESR signals from the QA iron-semiquinone and FZ+ non-haem iron components. We observed that Qs binding caused characteristic changes in the Qi ESR signal and confirmed that the characteristics of Qi depend on bicarbonate binding. The non-haem iron was oxidised only under conditions where bicarbonate was bound. The characteristics of bicarbonate binding were observed in Phormidium laminosum PS II, showing that the bicarbonate effect occurs in cyanobacteria. The results support a hypothesis which gives a central role to bicarbonate in providing the conditions for electron transfer in both cyanobacteria and higher plant PS II. It is suggested that bicarbonate binds at or close to the nonhaem iron and influences the characteristics of QA, Qa and the non-haem iron.

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Evidence for two tightly bound iron‐quinones in the electron acceptor complex of photosystem II

Cited by 15 publications

References 17 publications

Time resolved EPR on photosystem II particles after irreversible and reversible inhibition of water cleavage with high concentrations of acetate

Time resolved EPR on photosystem II particles after irreversible and reversible inhibition of water cleavage with high concentrations of acetate

Photosystem II heterogeneity: the acceptor side

Bicarbonate binding and the properties of photosystem II electron acceptors

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