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Bicarbonate-induced redox tuning in Photosystem II for regulation and protection. Proc Natl Acad Sci U S A 2016; 113:12144-12149. [PMID: 27791001 DOI: 10.1073/pnas.1608862113] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The midpoint potential (Em) of [Formula: see text], 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 (HCO3-) shifts the Em from ∼-145 mV to -70 mV. The higher values reported earlier are attributed to the loss of HCO3- during the titrations (pH 6.5, stirred under argon gassing). These findings mean that HCO3- binds less strongly when QA-• is present. Light-induced QA-• formation triggered HCO3- loss as manifest by the slowed electron transfer and the upshift in the Em of QA HCO3--depleted PSII also showed diminished light-induced 1O2 formation. This finding is consistent with a model in which the increase in the Em of [Formula: see text] promotes safe, direct [Formula: see text] charge recombination at the expense of the damaging back-reaction route that involves chlorophyll triplet-mediated 1O2 formation [Johnson GN, et al. (1995) Biochim Biophys Acta 1229:202-207]. These findings provide a redox tuning mechanism, in which the interdependence of the redox state of QA and the binding by HCO3- regulates and protects PSII. The potential for a sink (CO2) to source (PSII) feedback mechanism is discussed.
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Jajoo A, Katsuta N, Kawamori A. An EPR study of the pH dependence of formate effects on Photosystem II. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2006; 44:186-92. [PMID: 16762561 DOI: 10.1016/j.plaphy.2006.04.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2005] [Indexed: 05/10/2023]
Abstract
Effects of formate on rates of O(2) evolution and electron paramagnetic resonance (EPR) signals were observed in the oxygen evolving PS II membranes as a function of pH. In formate treated PS II membranes, decrease in pH value resulted in the inhibition of the O(2) evolving activity, a decrease in the intensity of S(2) state multiline signal but an increase in the intensity of the Q(A)(-)Fe(2+) EPR signal. Time-resolved EPR study of the Y(Z)(*) decay kinetics showed that the light-induced intensity of Y(Z)(*) EPR signal was proportional to the formate concentration. The change in the pH affected both the light-induced intensities and the decay rates of Y(Z)(*), which was found to be faster at lower pH. At 253 K, t(1/e) value of Y(Z)(*) decay kinetics was found to be 8-10 s at pH 6.0 and 18-21 s at pH 5.0. The results presented here indicate that the extent of inhibition at the donor and the acceptor side of PS II due to formate is pH dependent, being more effective at lower pH.
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Affiliation(s)
- Anjana Jajoo
- School of Life Sciences, Devi Ahilya Vishwavidyalaya, Indore 452 017, India.
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Nugent JH, Corrie AR, Demetriou C, Evans MC, Lockett CJ. Bicarbonate binding and the properties of photosystem II electron acceptors. FEBS Lett 2001. [DOI: 10.1016/0014-5793(88)81236-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Schansker G, van Rensen JJ. Mechanism of photoinhibition in pea thylakoids: effects of irradiance level and pH. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1996. [DOI: 10.1016/0005-2728(96)00080-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Moubarak-Milad M, Stemler A. Oxidation-reduction potential dependence of photosystem II carbonic anhydrase in maize thylakoids. Biochemistry 1994; 33:4432-8. [PMID: 8155662 DOI: 10.1021/bi00180a042] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
In characterizing the carbonic anhydrase (CA) found in maize thylakoid membranes, it was observed that the enzyme's activity was inhibited somewhat when the Hill oxidant, ferricyanide, was given in the dark [Stemler, A. (1986) Biochim. Biophys. Acta 850, 97-107]. In the present work, a redox titration of this effect shows that the CA activity is mediated by a component that has a midpoint potential (Em) of about 485 mV at pH 6.5 and a pH dependence of 60 mV/pH. These redox titration characteristics are identical to those of the redox mediator "D480", which modulates formate and bicarbonate binding affinity to photosystem II (PS II). Bicarbonate binds to PS II more readily, and CA activity is higher, when D480 is reduced, whereas both bicarbonate binding and thylakoid-bound CA activity are low when D480 is oxidized in the dark by ferricyanide. Both the low bicarbonate binding affinity and the low CA activity induced by the presence of ferricyanide are reversed by a single saturating flash of light. In contrast, the activity of soluble CA, which is extracted from maize mesophyll cytosol, does not exhibit any redox dependence in the range 400-550 mV. Furthermore, thylakoid-bound CA activity is inhibited by 5 mM ZnCl2 by as much as 75%, whereas the activity of soluble CA shows no significant decrease induced by ZnCl2. Also, at a medium potential of 400 mV, ferricyanide (1 mM) inhibits soluble CA activity by 88% and thylakoid-bound CA activity by only 18%. It is concluded from these results that CA activity observed in thylakoids arises from CA inherent to PS II and is not some form of contamination by soluble CA. Possible roles of CA in PS II reaction mechanisms are discussed.
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Jursinic PA, Stemler A. High rates of photosystem II electron flow occur in maize thylakoids when the high-affinity binding site for bicarbonate is empty of all monovalent anions or has bicarbonate bound. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1992. [DOI: 10.1016/s0005-2728(09)91018-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Diner BA, Petrouleas V. Formation by NO of nitrosyl adducts of redox components of the Photosystem II reaction center. II. Evidence that HCO−3/CO2 binds to the acceptor-side non-heme iron. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1990. [DOI: 10.1016/0005-2728(90)90225-s] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Sundby C, Larsson UK, Henrysson T. Effects of bicarbonate on thylakoid protein phosphorylation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1989. [DOI: 10.1016/s0005-2728(89)80259-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Blubaugh DJ, Govindjee. Kinetics of the bicarbonate effect and the number of bicarbonate-binding sites in thylakoid membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1988. [DOI: 10.1016/0005-2728(88)90237-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Blubaugh DJ. The molecular mechanism of the bicarbonate effect at the plastoquinone reductase site of photosynthesis. PHOTOSYNTHESIS RESEARCH 1988; 19:85-128. [PMID: 24425370 DOI: 10.1007/bf00114571] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/1987] [Accepted: 03/30/1988] [Indexed: 05/12/2023]
Abstract
It has been known for some time that bicarbonate reverses the inhibition, by formate under HCO3 (-)-depletion conditions, of electron transport in thylakoid membranes. It has been shown that the major effect is on the electron acceptor side of photosystem II, at the site of plastoquinone reduction. After presenting a historical introduction, and a minireview of the bicarbonate effect, we present a hypothesis on how HCO3 (-) functions in vivo as (a) a proton donor to the plastoquinone reductase site in the D1-D2 protein; and (b) a ligand to Fe(2+) in the QA-Fe-QB complex that keeps the D1-D2 proteins in their proper functional conformation. They key points of the hypothesis are: (1) HCO3 (-) forms a salt bridge between Fe(2+) and the D2 protein. The carboxyl group of HCO3 (-) is a bidentate ligand to Fe(2+), while the hydroxyl group H-bonds to a protein residue. (2) A second HCO3 (-) is involved in protonating a histidine near the QB site to stabilize the negative charge on QB. HCO3 (-) provides a rapidly available source of H(+) for this purpose. (3) After donation of a H(+), CO3 (2-) is replaced by another HCO3 (-). The high pKa of CO3 (2-) ensures rapid reprotonation from the bulk phase. (4) An intramembrane pool of HCO3 (-) is in equilibrium with a large number of low affinity sites. This pool is a H(+) buffering domain functionally connecting the external bulk phase with the quinones. The low affinity sites buffer the intrathylakoid [HCO3 (-)] against fluctuations in the intracellular CO2. (5) Low pH and high ionic strength are suggested to disrupt the HCO3 (-) salt bridge between Fe(2+) and D2. The resulting conformational change exposes the intramembrane HCO3 (-) pool and low affinity sites to the bulk phase.Two contrasting hypotheses for the action of formate are: (a) it functions to remove bicarbonate, and the low electron transport left in such samples is due to the left-over (or endogenous) bicarbonate in the system; or (b) bicarbonate is less of an inhibitor and so appears to relieve the inhibition by formate. Hypothesis (a) implies that HCO3 (-) is an essential requirement for electron transport through the plastoquinones (bound plastoquinones QA and QB and the plastoquinone pool) of photosystem II. Hypothesis (b) implies that HCO3 (-) does not play any significant role in vivo. Our conclusion is that hypothesis (a) is correct and HCO3 (-) is an essential requirement for electron transport on the electron acceptor side of PS II. This is based on several observations: (i) since HCO3 (-), not CO2, is the active species involved (Blubaugh and Govindjee 1986), the calculated concentration of this species (220 μM at pH 8, pH of the stroma) is much higher than the calculated dissociation constant (Kd) of 35-60 μM; thus, the likelihood of bound HCO3 (-) in ambient air is high; (ii) studies on HCO3 (-) effect in thylakoid samples with different chlorophyll concentrations suggest that the "left-over" (or "endogenous") electron flow in bicarbonate-depleted chloroplasts is due to "left-over" (or endogenous) HCO3 (-) remaining bound to the system (Blubaugh 1987).
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Affiliation(s)
- D J Blubaugh
- Department of Physiology & Biophysics, University of Illinois, 289 Morrill Hall, 505, South Goodwin Avenue, 61801, Urbana, IL, USA
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Jursinic P, Stemler A. CORRELATION BETWEEN THE BINDING OF FORMATE AND DECREASED RATES OF CHARGE TRANSFER THROUGH THE PHOTOSYSTEM II QUINONES. Photochem Photobiol 1986. [DOI: 10.1111/j.1751-1097.1986.tb09515.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Blubaugh DJ. Bicarbonate, not CO2, is the species required for the stimulation of Photosystem II electron transport. BIOCHIMICA ET BIOPHYSICA ACTA 1986; 848:147-51. [PMID: 3942713 DOI: 10.1016/0005-2728(86)90170-2] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Evidence is presented that the bicarbonate ion (HCO3-), not CO2, H2CO3 or CO32-, is the species that stimulates electron transport in Photosystem II from spinach (Spinacia oleracea). Advantage was taken of the pH dependence of the ratio of HCO3- to CO2 at equilibrium in order to vary effectively the concentration of one species while holding the other constant. The Hill reaction was stimulated in direct proportion with the equilibrium HCO3- concentration, but it was independent of the equilibrium CO2 concentration. The other two carbonic species, H2CO3 and CO32-, are also shown to have no direct involvement. It is suggested that HCO3- is the species which binds to the effector site.
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Eaton-Rye JJ. Electron transfer through photosystem II acceptors: Interaction with anions. PHOTOSYNTHESIS RESEARCH 1986; 10:365-379. [PMID: 24435384 DOI: 10.1007/bf00118302] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We present an overview of anionic interactions with the oxidation-reduction reactions of photosystem II (PSII) acceptors. In section 1, a framework is laid for the electron acceptor 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 (HCO3 (-)) effect, the location of the site of action of HCO3 (-), and its relationship to interactions with other anions. In section 3, we review data on the anion effects on the reoxidation of QA (-) and on the various reactions involved in the two-electron gate mechanism of PSII, and provide a hypothesis as to the action of HCO3 (-) on the protonation reactions. New data obtained by one of us (G) in collaboration with J.J.S. van Rensen, J.F.H Snel and W. Tonk for HCO3 (-)-depleted thylakoids, demonstrating the abolition of the binary oscillations contained within the periodicity of 4 observed for proton release, are also reviewed. In section 4, we comment on the 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 acceptor side of PSII, and comment on the possible physiological roles for HCO3 (-). Measurements of HCO3 (-) reversible anionic inhibition in intact cells of a green alga Scenedesmus are also reviewed.
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Van Rensen JJ, Snel JF. Regulation of photosynthetic electron transport by bicarbonate formate and herbicides in isolated broken and intact chloroplasts. PHOTOSYNTHESIS RESEARCH 1985; 6:231-246. [PMID: 24442922 DOI: 10.1007/bf00049280] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/1984] [Revised: 10/24/1984] [Indexed: 06/03/2023]
Abstract
In this paper, we have presented a minireview on the interaction of bicarbonate, formate and herbicides with the thylakoid membranes.The regulation of photosynthetic electron transport by bicarbonate, formate and herbicides is described. Bicarbonate, formate, and many herbicides act between the primary quinone electron acceptor QA and the plastoquinone pool. Many herbicides like the ureas, triazines and the phenol-type herbicides act, probably, by the displacement of the secondary quinone electron acceptor QB from its binding site on a QB-binding protein located at the acceptor side of Photosystem II. Formate appears to be an inhibitor of electron transport; this inhibition can be removed by the addition of bicarbonate. There appears to be an interaction of the herbicides with bicarbonate and/or It has been suggested that both the binding of a herbicide and the absence of bicarbonate may cause a conformational alteration of the environment of the QB-binding site. The alteration brought about by a herbicide decreases the affinity for another herbicide or for bicarbonate; the change caused by the absence of bicarbonate decreases the affinity for herbicides. Moreover, this change in conformation causes an inhibition of electron transport. A bicarbonate-effect in isolated intact chloroplasts is demonstrated.
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Affiliation(s)
- J J Van Rensen
- Laboratory of Plant Physiological Research, Agricultural University, Wageningen, The Netherlands
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The interaction between bicarbonate and the herbicide ioxynil in the thylakoid membrane and the effects of amino acid modification on bicarbonate action. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1982. [DOI: 10.1016/0005-2728(82)90028-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Bicarbonate effects on chlorophyll a fluorescence transients in the presence and the absence of diuron. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1982. [DOI: 10.1016/0005-2728(82)90012-3] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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