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Guo S, Wu Y, Aboueldahab M. Rapid oxygen isotopic exchange between bicarbonate and water during photosynthesis. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY. B, BIOLOGY 2024; 255:112924. [PMID: 38688041 DOI: 10.1016/j.jphotobiol.2024.112924] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2024] [Revised: 04/14/2024] [Accepted: 04/24/2024] [Indexed: 05/02/2024]
Abstract
Whether rapid oxygen isotopic exchange between bicarbonate and water occurs in photosynthesis is the key to determine the source of oxygen by classic 18O-labeled photosynthetic oxygen evolution experiments. Here we show that both Microcystis aeruginosa and Chlamydomonas reinhardtii utilize a significant proportion (>16%) of added bicarbonate as a carbon source for photosynthesis. However, oxygen isotopic signal in added bicarbonate cannot be traced in the oxygen in organic matter synthesized by these photosynthetic organisms. This contradicts the current photosynthesis theory, which states that photosynthetic oxygen evolution comes only from water, and oxygen in photosynthetic organic matter comes only from carbon dioxide. We conclude that the photosynthetic organisms undergo rapid exchange of oxygen isotope between bicarbonate and water during photosynthesis. At the same time, this study also provides isotopic evidence for a new mechanism that half of the oxygen in photosynthetic oxygen evolution comes from bicarbonate photolysis and half comes from water photolysis, which provides a new explanation for the bicarbonate effect, and suggests that the Kok-Joliot cycle of photosynthetic oxygen evolution, must be modified to include a molecule of bicarbonate in addition to one molecule of water which in turn must be incorporated into the cycle instead of two water molecules. Furthermore, this study provides a theoretical basis for constructing a newer artificial photosynthetic reactor coupling light reactions with the dark reactions.
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Affiliation(s)
- Shaogang Guo
- State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yanyou Wu
- State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.
| | - Mohamed Aboueldahab
- State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; University of Chinese Academy of Sciences, Beijing 100049, China; Department of Botany and Microbiology, Faculty of Science, South Valley University, Qena 83523, Egypt
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Shevela D, Kern JF, Govindjee G, Messinger J. Solar energy conversion by photosystem II: principles and structures. PHOTOSYNTHESIS RESEARCH 2023; 156:279-307. [PMID: 36826741 PMCID: PMC10203033 DOI: 10.1007/s11120-022-00991-y] [Citation(s) in RCA: 52] [Impact Index Per Article: 52.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Accepted: 12/01/2022] [Indexed: 05/23/2023]
Abstract
Photosynthetic water oxidation by Photosystem II (PSII) is a fascinating process because it sustains life on Earth and serves as a blue print for scalable synthetic catalysts required for renewable energy applications. The biophysical, computational, and structural description of this process, which started more than 50 years ago, has made tremendous progress over the past two decades, with its high-resolution crystal structures being available not only of the dark-stable state of PSII, but of all the semi-stable reaction intermediates and even some transient states. Here, we summarize the current knowledge on PSII with emphasis on the basic principles that govern the conversion of light energy to chemical energy in PSII, as well as on the illustration of the molecular structures that enable these reactions. The important remaining questions regarding the mechanism of biological water oxidation are highlighted, and one possible pathway for this fundamental reaction is described at a molecular level.
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Affiliation(s)
- Dmitry Shevela
- Department of Chemistry, Chemical Biological Centre, Umeå University, 90187, Umeå, Sweden.
| | - Jan F Kern
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Govindjee Govindjee
- Department of Plant Biology, Department of Biochemistry and Center of Biophysics & Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Johannes Messinger
- Department of Chemistry, Chemical Biological Centre, Umeå University, 90187, Umeå, Sweden.
- Molecular Biomimetics, Department of Chemistry - Ångström, Uppsala University, 75120, Uppsala, Sweden.
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Murali Manoj K, Bazhin N, Parashar A, Manekkathodi A, Wu Y. Comprehensive Analyses of the Enhancement of Oxygenesis in Photosynthesis by Bicarbonate and Effects of Diverse Additives: Z-scheme Explanation Versus Murburn Model. Physiology (Bethesda) 2022. [DOI: 10.5772/intechopen.106996] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
The Z-scheme electron transport chain (ETC) explanation for photosynthesis starts with the serial/sequential transfer of electrons sourced from water molecules bound at Photosystem II via a deterministic array of redox centers (of various stationary/mobile proteins), before \"sinking\" via the reduction of NADP+ bound at flavin-enzyme reductase. Several research groups’ finding that additives (like bicarbonate) enhance the light reaction had divided the research community because it violated the Z-scheme. The untenable aspects of the Z-scheme perception were demonstrated earlier and a murburn bioenergetics (a stochastic/parallel paradigm of ion-radical equilibriums) model was proposed to explain photophosphorylation and Emerson effect. Herein, we further support the murburn model with accurate thermodynamic calculations, which show that the cost of one-electron abstraction from bicarbonate [491 kJ/mol] is lower than water [527 kJ/mol]. Further, copious thioredoxin enables the capture of photoactivated electrons in milieu, which aid in the reduction of nicotinamide nucleotides. The diffusible reactive species (DRS) generated in milieu sponsor phosphorylations and oxygenic reactions. With structural analysis of Photosystems and interacting molecules, we chart out the equations of reactions that explain the loss of labeled O-atom traces in delocalized oxygenesis. Thus, this essay discredits the Z-scheme and explains key outstanding observations in the field.
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Abstract
In neutral medium (pH 7.0) [RuIIIRuII(µ-CO3)4(OH)]4− undergoes one electron oxidation to form [RuIIIRuIII(µ-CO3)4(OH)2]4− at an E1/2 of 0.85 V vs. NHE followed by electro-catalytic water oxidation at a potential ≥1.5 V. When the same electrochemical measurements are performed in bicarbonate medium (pH 8.3), the complex first undergoes one electron oxidation at an Epa of 0.86 V to form [RuIIIRuIII(µ-CO3)4(OH)2]4−. This complex further undergoes two step one electron oxidations to form RuIVRuIII and RuIVRuIV species at potentials (Epa) 1.18 and 1.35 V, respectively. The RuIVRuIII and RuIVRuIV species in bicarbonate solutions are [RuIVRuIII(µ-CO3)4(OH)(CO3)]4− and [RuIVRuIV(µ-CO3)4(O)(CO3)]4− based on density functional theory (DFT) calculations. The formation of HCO4− in the course of the oxidation has been demonstrated by DFT. The catalyst acts as homogeneous water oxidation catalyst, and after long term chronoamperometry, the absorption spectra does not change significantly. Each step has been found to follow a proton coupled electron transfer process (PCET) as obtained from the pH dependent studies. The catalytic current is found to follow linear relation with the concentration of the catalyst and bicarbonate. Thus, bicarbonate is involved in the catalytic process that is also evident from the generation of higher oxidation peaks in cyclic voltammetry. The detailed mechanism has been derived by DFT. A catalyst with no organic ligands has the advantage of long-time stability.
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Shevela D, Do HN, Fantuzzi A, Rutherford AW, Messinger J. Bicarbonate-Mediated CO 2 Formation on Both Sides of Photosystem II. Biochemistry 2020; 59:2442-2449. [PMID: 32574489 PMCID: PMC7467574 DOI: 10.1021/acs.biochem.0c00208] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Revised: 06/10/2020] [Indexed: 01/25/2023]
Abstract
The effect of bicarbonate (HCO3-) on photosystem II (PSII) activity was discovered in the 1950s, but only recently have its molecular mechanisms begun to be clarified. Two chemical mechanisms have been proposed. One is for the electron-donor side, in which mobile HCO3- enhances and possibly regulates water oxidation by acting as proton acceptor, after which it dissociates into CO2 and H2O. The other is for the electron-acceptor side, in which (i) reduction of the QA quinone leads to the release of HCO3- from its binding site on the non-heme iron and (ii) the Em potential of the QA/QA•- couple increases when HCO3- dissociates. This suggested a protective/regulatory role of HCO3- as it is known that increasing the Em of QA decreases the extent of back-reaction-associated photodamage. Here we demonstrate, using plant thylakoids, that time-resolved membrane-inlet mass spectrometry together with 13C isotope labeling of HCO3- allows donor- and acceptor-side formation of CO2 by PSII to be demonstrated and distinguished, which opens the door for future studies of the importance of both mechanisms under in vivo conditions.
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Affiliation(s)
- Dmitry Shevela
- Department
of Chemistry, Chemical Biological Centre, Umeå University, 90187 Umeå, Sweden
| | - Hoang-Nguyen Do
- Department
of Chemistry, Chemical Biological Centre, Umeå University, 90187 Umeå, Sweden
| | - Andrea Fantuzzi
- Department
of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - A. William Rutherford
- Department
of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Johannes Messinger
- Department
of Chemistry, Chemical Biological Centre, Umeå University, 90187 Umeå, Sweden
- Molecular
Biomimetics, Department of Chemistry-Ångström Laboratory, Uppsala University, 75120 Uppsala, Sweden
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Shevela D, Ananyev G, Vatland AK, Arnold J, Mamedov F, Eichacker LA, Dismukes GC, Messinger J. 'Birth defects' of photosystem II make it highly susceptible to photodamage during chloroplast biogenesis. PHYSIOLOGIA PLANTARUM 2019; 166:165-180. [PMID: 30693529 DOI: 10.1111/ppl.12932] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Revised: 01/17/2019] [Accepted: 01/18/2019] [Indexed: 06/09/2023]
Abstract
High solar flux is known to diminish photosynthetic growth rates, reducing biomass productivity and lowering disease tolerance. Photosystem II (PSII) of plants is susceptible to photodamage (also known as photoinactivation) in strong light, resulting in severe loss of water oxidation capacity and destruction of the water-oxidizing complex (WOC). The repair of damaged PSIIs comes at a high energy cost and requires de novo biosynthesis of damaged PSII subunits, reassembly of the WOC inorganic cofactors and membrane remodeling. Employing membrane-inlet mass spectrometry and O2 -polarography under flashing light conditions, we demonstrate that newly synthesized PSII complexes are far more susceptible to photodamage than are mature PSII complexes. We examined these 'PSII birth defects' in barley seedlings and plastids (etiochloroplasts and chloroplasts) isolated at various times during de-etiolation as chloroplast development begins and matures in synchronization with thylakoid membrane biogenesis and grana membrane formation. We show that the degree of PSII photodamage decreases simultaneously with biogenesis of the PSII turnover efficiency measured by O2 -polarography, and with grana membrane stacking, as determined by electron microscopy. Our data from fluorescence, QB -inhibitor binding, and thermoluminescence studies indicate that the decline of the high-light susceptibility of PSII to photodamage is coincident with appearance of electron transfer capability QA - → QB during de-etiolation. This rate depends in turn on the downstream clearing of electrons upon buildup of the complete linear electron transfer chain and the formation of stacked grana membranes capable of longer-range energy transfer.
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Affiliation(s)
- Dmitry Shevela
- Department of Chemistry, Chemical Biological Centre, Umeå University, S-90187, Umeå, Sweden
| | - Gennady Ananyev
- The Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ, 08854, USA
- Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ, 08854, USA
| | - Ann K Vatland
- Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, N-4036, Stavanger, Norway
| | - Janine Arnold
- Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, N-4036, Stavanger, Norway
| | - Fikret Mamedov
- Molecular Biomimetics, Department of Chemistry - Ångström Laboratory, Uppsala University, S-75237, Uppsala, Sweden
| | - Lutz A Eichacker
- Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, N-4036, Stavanger, Norway
| | - G Charles Dismukes
- The Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ, 08854, USA
- Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ, 08854, USA
| | - Johannes Messinger
- Department of Chemistry, Chemical Biological Centre, Umeå University, S-90187, Umeå, Sweden
- Molecular Biomimetics, Department of Chemistry - Ångström Laboratory, Uppsala University, S-75237, Uppsala, Sweden
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Mizrahi A, Meyerstein D. Plausible roles of carbonate in catalytic water oxidation. ADVANCES IN INORGANIC CHEMISTRY 2019. [DOI: 10.1016/bs.adioch.2019.03.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Shevela D, Björn LO. Evolution of the Z-scheme of photosynthesis: a perspective. PHOTOSYNTHESIS RESEARCH 2017; 133:5-15. [PMID: 28160125 DOI: 10.1007/s11120-016-0333-z] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Accepted: 12/29/2016] [Indexed: 05/08/2023]
Abstract
The concept of the Z-scheme of oxygenic photosynthesis is in all the textbooks. However, its evolution is not. We focus here mainly on some of the history of its biophysical aspects. We have arbitrarily divided here the 1941-2016 period into three sub-periods: (a) Origin of the concept of two light reactions: first hinted at, in 1941, by James Franck and Karl Herzfeld; described and explained, in 1945, by Eugene Rabinowitch; and a clear hypothesis, given in 1956 by Rabinowitch, of the then available cytochrome experiments: one light oxidizing it and another reducing it; (b) Experimental discovery of the two light reactions and two pigment systems and the Z-scheme of photosynthesis: Robert Emerson's discovery, in 1957, of enhancement in photosynthesis when two light beams (one in the far-red region, and the other of shorter wavelengths) are given together than when given separately; and the 1960 scheme of Robin Hill & Fay Bendall; and
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Affiliation(s)
- Dmitriy Shevela
- Department of Chemistry, Chemical Biological Centre, Umeå University, 90187, Umeå, Sweden
| | - Lars Olof Björn
- Department of Biology, Molecular Cell Biology, Lund University, Sölvegatan 35, 22362, Lund, Sweden
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Kadassery KJ, Dey SK, Friedman AE, Lacy DC. Exploring the Role of Carbonate in the Formation of an Organomanganese Tetramer. Inorg Chem 2017; 56:8748-8751. [DOI: 10.1021/acs.inorgchem.7b01438] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Karthika J. Kadassery
- Department of Chemistry, University at Buffalo, SUNY, Buffalo, New York 14260-3000, United States
| | - Suman Kr Dey
- Department of Chemistry, University at Buffalo, SUNY, Buffalo, New York 14260-3000, United States
| | - Alan E. Friedman
- Department of Chemistry, University at Buffalo, SUNY, Buffalo, New York 14260-3000, United States
| | - David C. Lacy
- Department of Chemistry, University at Buffalo, SUNY, Buffalo, New York 14260-3000, United States
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Shevela D, Arnold J, Reisinger V, Berends HM, Kmiec K, Koroidov S, Bue AK, Messinger J, Eichacker LA. Biogenesis of water splitting by photosystem II during de-etiolation of barley (Hordeum vulgare L.). PLANT, CELL & ENVIRONMENT 2016; 39:1524-1536. [PMID: 26836813 DOI: 10.1111/pce.12719] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Revised: 01/14/2016] [Accepted: 01/17/2016] [Indexed: 06/05/2023]
Abstract
Etioplasts lack thylakoid membranes and photosystem complexes. Light triggers differentiation of etioplasts into mature chloroplasts, and photosystem complexes assemble in parallel with thylakoid membrane development. Plastids isolated at various time points of de-etiolation are ideal to study the kinetic biogenesis of photosystem complexes during chloroplast development. Here, we investigated the chronology of photosystem II (PSII) biogenesis by monitoring assembly status of chlorophyll-binding protein complexes and development of water splitting via O2 production in plastids (etiochloroplasts) isolated during de-etiolation of barley (Hordeum vulgare L.). Assembly of PSII monomers, dimers and complexes binding outer light-harvesting antenna [PSII-light-harvesting complex II (LHCII) supercomplexes] was identified after 1, 2 and 4 h of de-etiolation, respectively. Water splitting was detected in parallel with assembly of PSII monomers, and its development correlated with an increase of bound Mn in the samples. After 4 h of de-etiolation, etiochloroplasts revealed the same water-splitting efficiency as mature chloroplasts. We conclude that the capability of PSII to split water during de-etiolation precedes assembly of the PSII-LHCII supercomplexes. Taken together, data show a rapid establishment of water-splitting activity during etioplast-to-chloroplast transition and emphasize that assembly of the functional water-splitting site of PSII is not the rate-limiting step in the formation of photoactive thylakoid membranes.
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Affiliation(s)
- Dmitriy Shevela
- Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, N-4036, Stavanger, Norway
- Department of Chemistry, Chemical Biological Centre, Umeå University, S-90187, Umeå, Sweden
| | - Janine Arnold
- Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, N-4036, Stavanger, Norway
| | - Veronika Reisinger
- Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, N-4036, Stavanger, Norway
| | - Hans-Martin Berends
- Department of Chemistry, Chemical Biological Centre, Umeå University, S-90187, Umeå, Sweden
| | - Karol Kmiec
- Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, N-4036, Stavanger, Norway
| | - Sergey Koroidov
- Department of Chemistry, Chemical Biological Centre, Umeå University, S-90187, Umeå, Sweden
- PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, Stanford, CA, 94305, USA
| | - Ann Kristin Bue
- Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, N-4036, Stavanger, Norway
| | - Johannes Messinger
- Department of Chemistry, Chemical Biological Centre, Umeå University, S-90187, Umeå, Sweden
| | - Lutz A Eichacker
- Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, N-4036, Stavanger, Norway
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Igamberdiev AU. Control of Rubisco function via homeostatic equilibration of CO2 supply. FRONTIERS IN PLANT SCIENCE 2015; 6:106. [PMID: 25767475 PMCID: PMC4341507 DOI: 10.3389/fpls.2015.00106] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Accepted: 02/09/2015] [Indexed: 05/09/2023]
Abstract
Rubisco is the most abundant protein on Earth that serves as the primary engine of carbon assimilation. It is characterized by a slow rate and low specificity for CO2 leading to photorespiration. We analyze here the challenges of operation of this enzyme as the main carbon fixation engine. The high concentration of Rubisco exceeds that of its substrate CO2 by 2-3 orders of magnitude; however, the total pool of available carbon in chloroplast, i.e., mainly bicarbonate, is comparable to the concentration of Rubisco active sites. This makes the reactant stationary assumption (RSA), which is essential as a condition of satisfying the Michaelis-Menten (MM) kinetics, valid if we assume that the delivery of CO2 from this pool is not limiting. The RSA is supported by active carbonic anhydrases (CA) that quickly equilibrate bicarbonate and CO2 pools and supply CO2 to Rubisco. While the operation of stromal CA is independent of light reactions, the thylakoidal CA associated with PSII and pumping CO2 from the thylakoid lumen is coordinated with the rate of electron transport, water splitting and proton gradient across the thylakoid membrane. At high CO2 concentrations, CA becomes less efficient (the equilibrium becomes unfavorable), so a deviation from the MM kinetics is observed, consistent with Rubisco reaching its Vmax at approximately 50% lower level than expected from the classical MM curve. Previously, this deviation was controversially explained by the limitation of RuBP regeneration. At low ambient CO2 and correspondingly limited capacity of the bicarbonate pool, its depletion at Rubisco sites is relieved in that the enzyme utilizes O2 instead of CO2, i.e., by photorespiration. In this process, CO2 is supplied back to Rubisco, and the chloroplastic redox state and energy level are maintained. It is concluded that the optimal performance of photosynthesis is achieved via the provision of continuous CO2 supply to Rubisco by carbonic anhydrases and photorespiration.
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Affiliation(s)
- Abir U. Igamberdiev
- *Correspondence: Abir U. Igamberdiev, Department of Biology, Memorial University of Newfoundland, 232 Elizabeth Avenue, St. John’s, NL A1B 3X9, Canada
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Koroidov S, Shevela D, Shutova T, Samuelsson G, Messinger J. Mobile hydrogen carbonate acts as proton acceptor in photosynthetic water oxidation. Proc Natl Acad Sci U S A 2014; 111:6299-304. [PMID: 24711433 PMCID: PMC4035973 DOI: 10.1073/pnas.1323277111] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cyanobacteria, algae, and plants oxidize water to the O2 we breathe, and consume CO2 during the synthesis of biomass. Although these vital processes are functionally and structurally well separated in photosynthetic organisms, there is a long-debated role for CO2/ in water oxidation. Using membrane-inlet mass spectrometry we demonstrate that acts as a mobile proton acceptor that helps to transport the protons produced inside of photosystem II by water oxidation out into the chloroplast's lumen, resulting in a light-driven production of O2 and CO2. Depletion of from the media leads, in the absence of added buffers, to a reversible down-regulation of O2 production by about 20%. These findings add a previously unidentified component to the regulatory network of oxygenic photosynthesis and conclude the more than 50-y-long quest for the function of CO2/ in photosynthetic water oxidation.
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Affiliation(s)
| | | | - Tatiana Shutova
- Department of Plant Physiology, Umeå Plant Science Centre, Umeå University, S-90187 Umeå, Sweden
| | - Göran Samuelsson
- Department of Plant Physiology, Umeå Plant Science Centre, Umeå University, S-90187 Umeå, Sweden
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