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Sipka G, Magyar M, Mezzetti A, Akhtar P, Zhu Q, Xiao Y, Han G, Santabarbara S, Shen JR, Lambrev PH, Garab G. Light-adapted charge-separated state of photosystem II: structural and functional dynamics of the closed reaction center. THE PLANT CELL 2021; 33:1286-1302. [PMID: 33793891 PMCID: PMC8225241 DOI: 10.1093/plcell/koab008] [Citation(s) in RCA: 55] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Accepted: 12/13/2020] [Indexed: 05/04/2023]
Abstract
Photosystem II (PSII) uses solar energy to oxidize water and delivers electrons for life on Earth. The photochemical reaction center of PSII is known to possess two stationary states. In the open state (PSIIO), the absorption of a single photon triggers electron-transfer steps, which convert PSII into the charge-separated closed state (PSIIC). Here, by using steady-state and time-resolved spectroscopic techniques on Spinacia oleracea and Thermosynechococcus vulcanus preparations, we show that additional illumination gradually transforms PSIIC into a light-adapted charge-separated state (PSIIL). The PSIIC-to-PSIIL transition, observed at all temperatures between 80 and 308 K, is responsible for a large part of the variable chlorophyll-a fluorescence (Fv) and is associated with subtle, dark-reversible reorganizations in the core complexes, protein conformational changes at noncryogenic temperatures, and marked variations in the rates of photochemical and photophysical reactions. The build-up of PSIIL requires a series of light-induced events generating rapidly recombining primary radical pairs, spaced by sufficient waiting times between these events-pointing to the roles of local electric-field transients and dielectric relaxation processes. We show that the maximum fluorescence level, Fm, is associated with PSIIL rather than with PSIIC, and thus the Fv/Fm parameter cannot be equated with the quantum efficiency of PSII photochemistry. Our findings resolve the controversies and explain the peculiar features of chlorophyll-a fluorescence kinetics, a tool to monitor the functional activity and the structural-functional plasticity of PSII in different wild-types and mutant organisms and under stress conditions.
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Affiliation(s)
- G�bor Sipka
- Institute of Plant Biology, Biological Research Centre, Szeged, Hungary
| | - Melinda Magyar
- Institute of Plant Biology, Biological Research Centre, Szeged, Hungary
| | - Alberto Mezzetti
- Universit� Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC) 91191 Gif-sur-Yvette, France
- Laboratoire de R�activit� de Surface UMR 7197, Sorbonne University, Paris, France
| | - Parveen Akhtar
- Institute of Plant Biology, Biological Research Centre, Szeged, Hungary
- ELI-ALPS, ELI-HU Nonprofit Ltd., Szeged, Hungary
| | - Qingjun Zhu
- Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
| | - Yanan Xiao
- Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
| | - Guangye Han
- Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
| | - Stefano Santabarbara
- Photosynthetic Research Unit, Institute of Biophysics, National Research Council of Italy, Milano, Italy
| | - Jian-Ren Shen
- Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
- Research Institute for Interdisciplinary Science, and Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan
| | - Petar H Lambrev
- Institute of Plant Biology, Biological Research Centre, Szeged, Hungary
- Author for correspondence: (G.G.), (P.H.L.)
| | - Győző Garab
- Institute of Plant Biology, Biological Research Centre, Szeged, Hungary
- Faculty of Science, University of Ostrava, Ostrava, Czech Republic
- Author for correspondence: (G.G.), (P.H.L.)
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Jennings RC, Belgio E, Zucchelli G. Photosystem I, when excited in the chlorophyll Q y absorption band, feeds on negative entropy. Biophys Chem 2017; 233:36-46. [PMID: 29287184 DOI: 10.1016/j.bpc.2017.12.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2017] [Revised: 12/10/2017] [Accepted: 12/16/2017] [Indexed: 11/27/2022]
Abstract
It is often suggested that Life may lay outside the normal laws of Physics and particularly of Thermodynamics, though this point of view is refuted by many. As the Living State may be thought of as an open system, often far from equilibrium, most attempts at placing Life under the umbrella of the laws of Physics have been based, particularly in recent years, on non-equilibrium Thermodynamics and particularly the Maximum Entropy Production Principle. In this view it is the dissipation of entropy (heat) which permits the ever increasing complexity of Living Systems in biological evolution and the maintenance of this complexity. However, these studies usually consider such biological entities as whole cells, organs, whole organisms and even Life itself at the entire terrestrial level. This requires making assumptions concerning the Living State, which are often not soundly based on observation and lack a defined model structure. The present study is based on an entirely different approach, in which a classical thermodynamic analysis of a well-defined biological nanoparticle, plant Photosystem I, is performed. This photosynthetic structure, which absorbs light and performs primary and secondary charge separation, operates with a quantum efficiency close to one. It is demonstrated that when monochromatic light is absorbed by the lowest lying electronic transition, the chlorophyll Qy transition, entropy production in the system bath plus entropy changes internal to the system are numerically less than the entropy decrease of the light field. A Second Law violation is therefore suggested for these experimental conditions. This conclusion, while at first sight is supportive of the famous and much discussed statement of Schroedinger, that "Life feeds on negentropy", is analysed and the conditions in which this statement may be considered valid for a Plant Photosystem are defined and delimited. The remarkably high quantum efficiency, leading to minimal entropy production (energy wastage), seems to suggest that evolution of Photosystem I has gone down the road of maximal energy efficiency as distinct from maximal entropy production. Photosystem I cannot be considered a maximum entropy dissipation structure.
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Affiliation(s)
- Robert C Jennings
- Consiglio Nazionale delle Ricerche, Istituto di Biofisica, sede di Milano, via Giovanni Celoria 26, 20133 Milano, Italy; Dipartimento di Bioscienze, Università degli Studi di Milano, via Giovanni Celoria 26, 20133 Milano, Italy.
| | - Erica Belgio
- Institute of Microbiology, CAS, Centre Algatech, Novohradska 237, Opatovický mlýn, Trebon 379 81, Czech Republic
| | - Giuseppe Zucchelli
- Consiglio Nazionale delle Ricerche, Istituto di Biofisica, sede di Milano, via Giovanni Celoria 26, 20133 Milano, Italy; Dipartimento di Bioscienze, Università degli Studi di Milano, via Giovanni Celoria 26, 20133 Milano, Italy
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3
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Fisher N, Kramer DM. Non-photochemical reduction of thylakoid photosynthetic redox carriers in vitro: relevance to cyclic electron flow around photosystem I? BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1837:1944-1954. [PMID: 25251244 DOI: 10.1016/j.bbabio.2014.09.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Revised: 09/07/2014] [Accepted: 09/14/2014] [Indexed: 01/17/2023]
Abstract
UNLABELLED Non-photochemical (dark) increases in chlorophyll a fluorescence yield associated with non-photochemical reduction of redox carriers (Fnpr) have been attributed to the reduction of plastoquinone (PQ) related to cyclic electron flow (CEF) around photosystem I. In vivo, this rise in fluorescence is associated with activity of the chloroplast plastoquinone reductase (plastid NAD(P)H plastoquinone oxidoreductase) complex. In contrast, this signal measured in isolated thylakoids has been attributed to the activity of the protein gradient regulation-5 (PGR5)/PGR5-like (PGRL1)-associated CEF pathway. Here, we report a systematic experimentation on the origin of Fnpr in isolated thylakoids. Addition of NADPH and ferredoxin to isolated spinach thylakoids resulted in the reduction of the PQ pool, but neither its kinetics nor its inhibitor sensitivities matched those of Fnpr. Notably, Fnpr was more rapid than PQ reduction, and completely insensitive to inhibitors of the PSII QB site and oxygen evolving complex as well as inhibitors of the cytochrome b6f complex. We thus conclude that Fnpr in isolated thylakoids is not a result of redox equilibrium with bulk PQ. Redox titrations and fluorescence emission spectra imply that Fnpr is dependent on the reduction of a low potential redox component (Em about − 340 mV) within photosystem II (PSII), and is likely related to earlier observations of low potential variants of QA within a subpopulation of PSII that is directly reducible by ferredoxin. The implications of these results for our understanding of CEF and other photosynthetic processes are discussed.
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Affiliation(s)
- Nicholas Fisher
- MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA
| | - David M Kramer
- MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA; Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
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Klauss A, Haumann M, Dau H. Seven Steps of Alternating Electron and Proton Transfer in Photosystem II Water Oxidation Traced by Time-Resolved Photothermal Beam Deflection at Improved Sensitivity. J Phys Chem B 2014; 119:2677-89. [DOI: 10.1021/jp509069p] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- André Klauss
- Freie Universität Berlin, Institut für Experimentalphysik, 14195 Berlin, Germany
| | - Michael Haumann
- Freie Universität Berlin, Institut für Experimentalphysik, 14195 Berlin, Germany
| | - Holger Dau
- Freie Universität Berlin, Institut für Experimentalphysik, 14195 Berlin, Germany
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Schansker G, Tóth SZ, Holzwarth AR, Garab G. Chlorophyll a fluorescence: beyond the limits of the Q(A) model. PHOTOSYNTHESIS RESEARCH 2014; 120:43-58. [PMID: 23456268 DOI: 10.1007/s11120-013-9806-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2012] [Accepted: 02/18/2013] [Indexed: 05/03/2023]
Abstract
Chlorophyll a fluorescence is a non-invasive tool widely used in photosynthesis research. According to the dominant interpretation, based on the model proposed by Duysens and Sweers (1963, Special Issue of Plant and Cell Physiology, pp 353-372), the fluorescence changes reflect primarily changes in the redox state of Q(A), the primary quinone electron acceptor of photosystem II (PSII). While it is clearly successful in monitoring the photochemical activity of PSII, a number of important observations cannot be explained within the framework of this simple model. Alternative interpretations have been proposed but were not supported satisfactorily by experimental data. In this review we concentrate on the processes determining the fluorescence rise on a dark-to-light transition and critically analyze the experimental data and the existing models. Recent experiments have provided additional evidence for the involvement of a second process influencing the fluorescence rise once Q(A) is reduced. These observations are best explained by a light-induced conformational change, the focal point of our review. We also want to emphasize that-based on the presently available experimental findings-conclusions on α/ß-centers, PSII connectivity, and the assignment of FV/FM to the maximum PSII quantum yield may require critical re-evaluations. At the same time, it has to be emphasized that for a deeper understanding of the underlying physical mechanism(s) systematic studies on light-induced changes in the structure and reaction kinetics of the PSII reaction center are required.
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Affiliation(s)
- Gert Schansker
- Institute of Plant Biology, Biological Research Center Szeged, Hungarian Academy of Sciences, Szeged, 6701, Hungary,
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6
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Onidas D, Sipka G, Asztalos E, Maróti P. Mutational control of bioenergetics of bacterial reaction center probed by delayed fluorescence. BIOCHIMICA ET BIOPHYSICA ACTA 2013; 1827:1191-9. [PMID: 23685111 DOI: 10.1016/j.bbabio.2013.05.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 05/01/2013] [Accepted: 05/09/2013] [Indexed: 10/26/2022]
Abstract
The free energy gap between the metastable charge separated state P(+)QA(-) and the excited bacteriochlorophyll dimer P* was measured by delayed fluorescence of the dimer in mutant reaction center proteins of the photosynthetic bacterium Rhodobacter sphaeroides. The mutations were engineered both at the donor (L131L, M160L, M197F and M202H) and acceptor (M265I and M234E) sides. While the donor side mutations changed systematically the number of H-bonds to P, the acceptor side mutations modified the energetics of QA by altering the van-der-Waals and electronic interactions (M265IT) and H-bond network to the acidic cluster around QB (M234EH, M234EL, M234EA and M234ER). All mutants decreased the free energy gap of the wild type RC (~890meV), i.e. destabilized the P(+)QA(-) charge pair by 60-110meV at pH8. Multiple modifications in the hydrogen bonding pattern to P resulted in systematic changes of the free energy gap. The destabilization showed no pH-dependence (M234 mutants) or slight increase (WT, donor-side mutants and M265IT above pH8) with average slope of 10-15meV/pH unit over the 6-10.5pH range. In wild type and donor-side mutants, the free energy change of the charge separation consisted of mainly enthalpic term but the acceptor side mutants showed increased entropic (even above that of enthalpic) contributions. This could include softening the structure of the iron ligand (M234EH) and the QA binding pocket (M265IT) and/or increase of the multiplicity of the electron transfer of charge separation in the acceptor side upon mutation.
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Affiliation(s)
- Delphine Onidas
- Laboratoire de Chimie Physique UMR 8000, Batiment 350, Orsay-Cedex, Université de Paris-Sud, 91405, France
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Photosystem trap energies and spectrally-dependent energy-storage efficiencies in the Chl d-utilizing cyanobacterium, Acaryochloris marina. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1827:255-65. [DOI: 10.1016/j.bbabio.2012.11.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 10/08/2012] [Accepted: 11/02/2012] [Indexed: 12/27/2022]
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Alternating electron and proton transfer steps in photosynthetic water oxidation. Proc Natl Acad Sci U S A 2012; 109:16035-40. [PMID: 22988080 DOI: 10.1073/pnas.1206266109] [Citation(s) in RCA: 146] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Water oxidation by cyanobacteria, algae, and plants is pivotal in oxygenic photosynthesis, the process that powers life on Earth, and is the paradigm for engineering solar fuel-production systems. Each complete reaction cycle of photosynthetic water oxidation requires the removal of four electrons and four protons from the catalytic site, a manganese-calcium complex and its protein environment in photosystem II. In time-resolved photothermal beam deflection experiments, we monitored apparent volume changes of the photosystem II protein associated with charge creation by light-induced electron transfer (contraction) and charge-compensating proton relocation (expansion). Two previously invisible proton removal steps were detected, thereby filling two gaps in the basic reaction-cycle model of photosynthetic water oxidation. In the S(2) → S(3) transition of the classical S-state cycle, an intermediate is formed by deprotonation clearly before electron transfer to the oxidant (Y Z OX). The rate-determining elementary step (τ, approximately 30 µs at 20 °C) in the long-distance proton relocation toward the protein-water interface is characterized by a high activation energy (E(a) = 0.46 ± 0.05 eV) and strong H/D kinetic isotope effect (approximately 6). The characteristics of a proton transfer step during the S(0) → S(1) transition are similar (τ, approximately 100 µs; E(a) = 0.34 ± 0.08 eV; kinetic isotope effect, approximately 3); however, the proton removal from the Mn complex proceeds after electron transfer to . By discovery of the transient formation of two further intermediate states in the reaction cycle of photosynthetic water oxidation, a temporal sequence of strictly alternating removal of electrons and protons from the catalytic site is established.
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Fast structural changes (200-900ns) may prepare the photosynthetic manganese complex for oxidation by the adjacent tyrosine radical. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1817:1196-207. [PMID: 22579714 DOI: 10.1016/j.bbabio.2012.04.017] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Revised: 04/25/2012] [Accepted: 04/30/2012] [Indexed: 11/20/2022]
Abstract
The Mn complex of photosystem II (PSII) cycles through 4 semi-stable states (S(0) to S(3)). Laser-flash excitation of PSII in the S(2) or S(3) state induces processes with time constants around 350ns, which have been assigned previously to energetic relaxation of the oxidized tyrosine (Y(Z)(ox)). Herein we report monitoring of these processes in the time domain of hundreds of nanoseconds by photoacoustic (or 'optoacoustic') experiments involving pressure-wave detection after excitation of PSII membrane particles by ns-laser flashes. We find that specifically for excitation of PSII in the S(2) state, nuclear rearrangements are induced which amount to a contraction of PSII by at least 30Å(3) (time constant of 350ns at 25°C; activation energy of 285+/-50meV). In the S(3) state, the 350-ns-contraction is about 5 times smaller whereas in S(0) and S(1), no volume changes are detectable in this time domain. It is proposed that the classical S(2)=>S(3) transition of the Mn complex is a multi-step process. The first step after Y(Z)(ox) formation involves a fast nuclear rearrangement of the Mn complex and its protein-water environment (~350ns), which may serve a dual role: (1) The Mn- complex entity is prepared for the subsequent proton removal and electron transfer by formation of an intermediate state of specific (but still unknown) atomic structure. (2) Formation of the structural intermediate is associated (necessarily) with energetic relaxation and thus stabilization of Y(Z)(ox) so that energy losses by charge recombination with the Q(A)(-) anion radical are minimized. The intermediate formed within about 350ns after Y(Z)(ox) formation in the S(2)-state is discussed in the context of two recent models of the S(2)=>S(3) transition of the water oxidation cycle. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: From Natural to Artificial.
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Hou X, Hou HJM. Roles of manganese in photosystem II dynamics to irradiations and temperatures. ACTA ACUST UNITED AC 2012. [DOI: 10.1007/s11515-012-1214-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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11
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Yan C, Schofield O, Dubinsky Z, Mauzerall D, Falkowski PG, Gorbunov MY. Photosynthetic energy storage efficiency in Chlamydomonas reinhardtii, based on microsecond photoacoustics. PHOTOSYNTHESIS RESEARCH 2011; 108:215-224. [PMID: 21894460 DOI: 10.1007/s11120-011-9682-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Accepted: 08/15/2011] [Indexed: 05/31/2023]
Abstract
Using a novel, pulsed micro-second time-resolved photoacoustic (PA) instrument, we measured thermal dissipation and energy storage (ES) in the intact cells of wild type (WT) Chlamydomonas reinhardtii, and mutants lacking either PSI or PSII reaction centers (RCs). On this time scale, the kinetic contributions of the thermal expansion component due to heat dissipation of absorbed energy and the negative volume change due to electrostriction induced by charge separation in each of the photosystems could be readily distinguished. Kinetic analysis revealed that PSI and PSII RCs exhibit strikingly different PA signals where PSI is characterized by a strong electrostriction signal and a weak thermal expansion component while PSII has a small electrostriction component and large thermal expansion. The calculated ES efficiencies at ~10 μs were estimated to be 80 ± 5 and 50 ± 13% for PSII-deficient mutants and PSI-deficient mutants, respectively, and 67 ± 2% for WT. The overall ES efficiency was positively correlated with the ratio of PSI to PSI + PSII. Our results suggest that the shallow excitonic trap in PSII limits the efficiency of ES as a result of an evolutionary frozen metabolic framework of two photosystems in all oxygenic photoautotrophs.
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Affiliation(s)
- Chengyi Yan
- Environmental Biophysics and Molecular Ecology Program, Institute of Marine and Coastal Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA
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Listening to PS II: Enthalpy, entropy, and volume changes. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2011; 104:357-65. [DOI: 10.1016/j.jphotobiol.2011.03.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2010] [Revised: 03/05/2011] [Accepted: 03/08/2011] [Indexed: 11/17/2022]
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Müh F, Glöckner C, Hellmich J, Zouni A. Light-induced quinone reduction in photosystem II. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2011; 1817:44-65. [PMID: 21679684 DOI: 10.1016/j.bbabio.2011.05.021] [Citation(s) in RCA: 163] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2011] [Revised: 05/20/2011] [Accepted: 05/23/2011] [Indexed: 10/18/2022]
Abstract
The photosystem II core complex is the water:plastoquinone oxidoreductase of oxygenic photosynthesis situated in the thylakoid membrane of cyanobacteria, algae and plants. It catalyzes the light-induced transfer of electrons from water to plastoquinone accompanied by the net transport of protons from the cytoplasm (stroma) to the lumen, the production of molecular oxygen and the release of plastoquinol into the membrane phase. In this review, we outline our present knowledge about the "acceptor side" of the photosystem II core complex covering the reaction center with focus on the primary (Q(A)) and secondary (Q(B)) quinones situated around the non-heme iron with bound (bi)carbonate and a comparison with the reaction center of purple bacteria. Related topics addressed are quinone diffusion channels for plastoquinone/plastoquinol exchange, the newly discovered third quinone Q(C), the relevance of lipids, the interactions of quinones with the still enigmatic cytochrome b559 and the role of Q(A) in photoinhibition and photoprotection mechanisms. This article is part of a Special Issue entitled: Photosystem II.
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Affiliation(s)
- Frank Müh
- Max-Volmer-Laboratorium für Biophysikalische Chemie, Technische Universität Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany
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Methodology of pulsed photoacoustics and its application to probe photosystems and receptors. SENSORS 2010; 10:5642-67. [PMID: 22219680 PMCID: PMC3247725 DOI: 10.3390/s100605642] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/23/2010] [Revised: 05/27/2010] [Accepted: 05/27/2010] [Indexed: 11/16/2022]
Abstract
We review recent advances in the methodology of pulsed time-resolved photoacoustics and its application to studies of photosynthetic reaction centers and membrane receptors such as the G protein-coupled receptor rhodopsin. The experimental parameters accessible to photoacoustics include molecular volume change and photoreaction enthalpy change. Light-driven volume change secondary to protein conformational changes or electrostriction is directly related to the photoreaction and thus can be a useful measurement of activity and function. The enthalpy changes of the photochemical reactions observed can be measured directly by photoacoustics. With the measurement of enthalpy change, the reaction entropy can also be calculated when free energy is known. Dissecting the free energy of a photoreaction into enthalpic and entropic components may provide critical information about photoactivation mechanisms of photosystems and photoreceptors. The potential limitations and future applications of time-resolved photoacoustics are also discussed.
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Klauss A, Krivanek R, Dau H, Haumann M. Energetics and kinetics of photosynthetic water oxidation studied by photothermal beam deflection (PBD) experiments. PHOTOSYNTHESIS RESEARCH 2009; 102:499-509. [PMID: 19330462 DOI: 10.1007/s11120-009-9417-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2008] [Accepted: 03/09/2009] [Indexed: 05/27/2023]
Abstract
Determination of thermodynamic parameters of water oxidation at the photosystem II (PSII) manganese complex is a major challenge. Photothermal beam deflection (PBD) spectroscopy determines enthalpy changes (ΔH) and apparent volume changes which are coupled with electron transfer in the S-state cycle (Krivanek R, Dau H, Haumann M (2008) Biophys J 94: 1890–1903). Recent PBD results on formation of the Q⁻(A)/Y(•+)(Z) radical pair suggest a value of ΔH similar to the free energy change, ΔG, of -540±40 meV previously determined by the analysis of recombination fluorescence, but presently the uncertainty range of ΔH values determined by PBD is still high (±250 meV). In the oxygen-evolving transition, S₃−−>S₀, the enthalpy change may be close to zero. A prominent non-thermal signal is associated with both Q⁻(A)/Y(•+)(Z) formation (<1 μs) and the S₃−−>S₀ transition (~1 ms). The observed (apparent) volume expansion (ΔV of about +40 ų per PSII unit) in the S₃−−>S₀ transition seems to revert, at least partially, the contractions on lower S-transitions and may also comprise contributions from O₂ and proton release. The observed volume changes show that the S₃−−>S₀ transition is accompanied by significant nuclear movements, which likely are of importance with respect to energetics and mechanism of photosynthetic water oxidation. Detailed PBD studies on all S-transitions will contribute to the progress in PSII research by providing insights not accessible by other spectroscopic methods.
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Affiliation(s)
- André Klauss
- FB Physik, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
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Hou HJM, Shen G, Boichenko VA, Golbeck JH, Mauzerall D. Thermodynamics of Charge Separation of Photosystem I in the menA and menB Null Mutants of Synechocystis sp. PCC 6803 Determined by Pulsed Photoacoustics. Biochemistry 2009; 48:1829-37. [DOI: 10.1021/bi801951t] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Harvey J. M. Hou
- Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, Massachusetts 02747, Department of Biochemistry and Molecular Biology and Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino 142290, Russia, and The Rockefeller University, 1230 York Avenue, New York, New York 10065
| | - Gaozhong Shen
- Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, Massachusetts 02747, Department of Biochemistry and Molecular Biology and Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino 142290, Russia, and The Rockefeller University, 1230 York Avenue, New York, New York 10065
| | - Vladimir A. Boichenko
- Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, Massachusetts 02747, Department of Biochemistry and Molecular Biology and Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino 142290, Russia, and The Rockefeller University, 1230 York Avenue, New York, New York 10065
| | - John H. Golbeck
- Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, Massachusetts 02747, Department of Biochemistry and Molecular Biology and Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino 142290, Russia, and The Rockefeller University, 1230 York Avenue, New York, New York 10065
| | - David Mauzerall
- Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, Massachusetts 02747, Department of Biochemistry and Molecular Biology and Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino 142290, Russia, and The Rockefeller University, 1230 York Avenue, New York, New York 10065
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17
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Shibata Y, Akai S, Kasahara T, Ikegami I, Itoh S. Temperature-dependent energy gap of the primary charge separation in photosystem I: study of delayed fluorescence at 77-268 K. J Phys Chem B 2008; 112:6695-702. [PMID: 18461984 DOI: 10.1021/jp710551e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The dynamics of fluorescence decay and charge recombination were studied in the ether-extracted photosystem I reaction center isolated from spinach with picosecond resolution over a wide time range up to 100 ns. At all temperatures from 268 to 77 K, a slow fluorescence decay component with a 30-40 ns lifetime was detected. This component was interpreted as a delayed fluorescence emitted from the singlet excited state of the primary donor P700*, which is repopulated through charge recombination that was increased by the lack of secondary acceptor phylloquinone in the sample. Analysis of the fluorescence kinetics allowed estimation of the standard free-energy difference -DeltaG between P700* and the primary radical pair (P700(+)A0(-)) state over a wide temperature range. The values of -DeltaG were estimated to be 160/36 meV at 268/77 K, indicating its high sensitivity to temperature. A temperature-dependent -DeltaG value was also estimated in the delayed fluorescence of the isolated photosystem I in which the secondary acceptor quinone was partially prereduced by preillumination in the presence of dithionite. The results revealed that the temperature-dependent -DeltaG is a universal phenomenon common with the purple bacterial reaction centers, photosystem II and photosystem I reaction centers.
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Affiliation(s)
- Yutaka Shibata
- Division of Material Science (Physics), Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan.
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18
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Enthalpy changes during photosynthetic water oxidation tracked by time-resolved calorimetry using a photothermal beam deflection technique. Biophys J 2007; 94:1890-903. [PMID: 17993488 DOI: 10.1529/biophysj.107.117085] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The energetics of the individual reaction steps in the catalytic cycle of photosynthetic water oxidation at the Mn(4)Ca complex of photosystem II (PSII) are of prime interest. We studied the electron transfer reactions in oxygen-evolving PSII membrane particles from spinach by a photothermal beam deflection technique, allowing for time-resolved calorimetry in the micro- to millisecond domain. For an ideal quantum yield of 100%, the enthalpy change, DeltaH, coupled to the formation of the radical pair Y(Z)(.+)Q(A)(-) (where Y(Z) is Tyr-161 of the D1 subunit of PSII) is estimated as -820 +/- 250 meV. For a lower quantum yield of 70%, the enthalpy change is estimated to be -400 +/- 250 meV. The observed nonthermal signal possibly is due to a contraction of the PSII protein volume (apparent DeltaV of about -13 A(3)). For the first time, the enthalpy change of the O(2)-evolving transition of the S-state cycle was monitored directly. Surprisingly, the reaction is only slightly exergonic. A value of DeltaH(S(3)-->S(0)) of -210 meV is estimated, but also an enthalpy change of zero is within the error range. A prominent nonthermal photothermal beam deflection signal (apparent DeltaV of about +42 A(3)) may reflect O(2) and proton release from the manganese complex, but also reorganization of the protein matrix.
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19
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Jennings RC, Belgio E, Casazza AP, Garlaschi FM, Zucchelli G. Entropy consumption in primary photosynthesis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2007; 1767:1194-7; discussion 1198-9. [PMID: 17900522 DOI: 10.1016/j.bbabio.2007.08.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2007] [Revised: 07/20/2007] [Accepted: 08/08/2007] [Indexed: 10/22/2022]
Abstract
Knox and Parson have objected to our previous conclusion on possible negative entropy production during primary photochemistry, i.e., from photon absorption to primary charge separation, by considering a pigment system in which primary photochemistry is not specifically considered. This approach does not address our proposal. They suggest that when a pigment absorbs light and passes to an excited state, its entropy increases by hnu/T. This point is discussed in two ways: (i) from considerations based on the energy gap law for excited state relaxation; (ii) using classical thermodynamics, in which free energy is introduced into the pigment (antenna) system by photon absorption. Both approaches lead us to conclude that the excited state and the ground state are isoentropic, in disagreement with Knox and Parson. A discussion on total entropy changes specifically during the charge separation process itself indicates that this process may be almost isoentropic and thus our conclusions on possible negentropy production associated with the sequence of reactions which go from light absorption to the first primary charge separation event, due to its very high thermodynamic efficiency, remain unchanged.
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Affiliation(s)
- Robert C Jennings
- CNR Istituto di Biofisica-Sede di Milano, via Celoria 26, 20133 Milan, Italy.
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20
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Boichenko VA, Pinevich AV, Stadnichuk IN. Association of chlorophyll a/b-binding Pcb proteins with photosystems I and II in Prochlorothrix hollandica. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2007; 1767:801-6. [PMID: 17174934 DOI: 10.1016/j.bbabio.2006.11.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2006] [Revised: 10/25/2006] [Accepted: 11/01/2006] [Indexed: 11/28/2022]
Abstract
Action spectra for photosystem II (PSII)-driven oxygen evolution and of photosystem I (PSI)-mediated H(2) photoproduction and photoinhibition of respiration were used to determine the participation of chlorophyll (Chl) a/b-binding Pcb proteins in the functions of pigment apparatus of Prochlorothrix hollandica. Comparison of the in situ action spectra with absorption spectra of PSII and PSI complexes isolated from the cyanobacterium Synechocystis 6803 revealed a shoulder at 650 nm that indicated presence of Chl b in the both photosystems of P. hollandica. Fitting of two action spectra to absorption spectrum of the cells showed a chlorophyll ratio of 4:1 in favor of PSI. Effective antenna sizes estimated from photochemical cross-sections of the relevant photoreactions were found to be 192+/-28 and 139+/-15 chlorophyll molecules for the competent PSI and PSII reaction centers, respectively. The value for PSI is in a quite good agreement with previous electron microscopy data for isolated Pcb-PSI supercomplexes from P. hollandica that show a trimeric PSI core surrounded by a ring of 18 Pcb subunits. The antenna size of PSII implies that the PSII core dimers are associated with approximately 14 Pcb light-harvesting proteins, and form the largest known Pcb-PSII supercomplexes.
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Affiliation(s)
- Vladimir A Boichenko
- Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino 142290, Russia.
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21
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Dau H, Haumann M. Eight steps preceding O-O bond formation in oxygenic photosynthesis--a basic reaction cycle of the Photosystem II manganese complex. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2007; 1767:472-83. [PMID: 17442260 DOI: 10.1016/j.bbabio.2007.02.022] [Citation(s) in RCA: 129] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2006] [Revised: 02/16/2007] [Accepted: 02/28/2007] [Indexed: 10/23/2022]
Abstract
In oxygenic photosynthesis, water is split at a Mn(4)Ca complex bound to the proteins of photosystem II (PSII). Powered by four quanta of visible light, four electrons and four protons are removed from two water molecules before dioxygen is released. By this process, water becomes an inexhaustible source of the protons and electrons needed for primary biomass formation. On the basis of structural and spectroscopic data, we recently have introduced a basic reaction cycle of water oxidation which extends the classical S-state cycle [B. Kok, B. Forbush, M. McGloin, Cooperation of charges in photosynthetic O2 evolution- I. A linear four-step mechanism, Photochem. Photobiol. 11 (1970) 457-475] by taking into account also the role and sequence of deprotonation events [H. Dau, M. Haumann, Reaction cycle of photosynthetic water oxidation in plants and cyanobacteria, Science 312 (2006) 1471-1472]. We propose that the outwardly convoluted and irregular events of the classical S-state cycle are governed by a simple underlying principle: protons and electrons are removed strictly alternately from the Mn complex. Starting in I(0), eight successive steps of alternate proton and electron removal lead to I(8) and only then the O-O bond is formed. Thus not only four oxidizing equivalents, but also four bases are accumulated prior to the onset of dioxygen formation. After reviewing the kinetic properties of the individual S-state transition, we show that the proposed basic model explains a large body of experimental results straightforwardly. Furthermore we discuss how the I-cycle model addresses the redox-potential problem of PSII water oxidation and we propose that the accumulated bases facilitate dioxygen formation by acting as proton acceptors.
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Affiliation(s)
- Holger Dau
- Freie Universität Berlin, FB PhysikArnimallee 14, D-14195 Berlin, Germany.
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22
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Kiang NY, Siefert J, Blankenship RE. Spectral signatures of photosynthesis. I. Review of Earth organisms. ASTROBIOLOGY 2007; 7:222-51. [PMID: 17407409 DOI: 10.1089/ast.2006.0105] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Why do plants reflect in the green and have a "red edge" in the red, and should extrasolar photosynthesis be the same? We provide (1) a brief review of how photosynthesis works, (2) an overview of the diversity of photosynthetic organisms, their light harvesting systems, and environmental ranges, (3) a synthesis of photosynthetic surface spectral signatures, and (4) evolutionary rationales for photosynthetic surface reflectance spectra with regard to utilization of photon energy and the planetary light environment. We found the "near-infrared (NIR) end" of the red edge to trend from blue-shifted to reddest for (in order) snow algae, temperate algae, lichens, mosses, aquatic plants, and finally terrestrial vascular plants. The red edge is weak or sloping in lichens. Purple bacteria exhibit possibly a sloping edge in the NIR. More studies are needed on pigment-protein complexes, membrane composition, and measurements of bacteria before firm conclusions can be drawn about the role of the NIR reflectance. Pigment absorbance features are strongly correlated with features of atmospheric spectral transmittance: P680 in Photosystem II with the peak surface incident photon flux density at approximately 685 nm, just before an oxygen band at 687.5 nm; the NIR end of the red edge with water absorbance bands and the oxygen A-band at 761 nm; and bacteriochlorophyll reaction center wavelengths with local maxima in atmospheric and water transmittance spectra. Given the surface incident photon flux density spectrum and resonance transfer in light harvesting, we propose some rules with regard to where photosynthetic pigments will peak in absorbance: (1) the wavelength of peak incident photon flux; (2) the longest available wavelength for core antenna or reaction center pigments; and (3) the shortest wavelengths within an atmospheric window for accessory pigments. That plants absorb less green light may not be an inefficient legacy of evolutionary history, but may actually satisfy the above criteria.
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Affiliation(s)
- Nancy Y Kiang
- NASA Goddard Institute for Space Studies, New York, New York 10025, USA.
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23
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Hou HJ, Mauzerall D. The A-Fx to F(A/B) step in synechocystis 6803 photosystem I is entropy driven. J Am Chem Soc 2006; 128:1580-6. [PMID: 16448129 PMCID: PMC2597517 DOI: 10.1021/ja054870y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
We have previously reported the enthalpy and volume changes of charge separation in photosystem I from Synechocystis 6803 using pulsed photoacoustics on the microsecond time scale, assigned to the electron-transfer reaction from excited-state P(700) to F(A/B) iron sulfur clusters. In the present work, we focus on the thermodynamics of two steps in photosystem I: (1) P(700) --> A(1)(-)F(X) (<10 ns) and (2) A(1)(-)F(X) --> F(A/B)(-) (20-200 ns). The fit by convolution of photoacoustic waves on the nanosecond and microsecond time scales resolved two kinetic components: (1) a prompt component (<10 ns) with large negative enthalpy (-0.8 +/- 0.1 eV) and large volume change (-23 +/- 2 A(3)), which are assigned to the P(700) --> A(1)(-)F(X) step, and (2) a component with approximately 200 ns lifetime, which has a positive enthalpy (+0.4 +/- 0.2 eV) and a small volume change (-3 +/- 2 A(3)) that are attributed to the A(1)(-)F(X) --> F(A/B)(-) step. For the fast reaction using the redox potentials of A(1)F(X) (-0.67 V) and P(700) (+0.45 V) and the energy of P(700) (1.77 eV), the free energy change for the P(700) --> A(1)(-)F(X) step is -0.63 eV, and thus the entropy change (TDeltaS, T = 25 degrees C) is -0.2 +/- 0.3 eV. For the slow reaction, A(1)(-)F(X) --> F(A/B)(-), taking the free energy of -0.14 eV [Santabara, S.; Heathcote, P; Evans, C. W. Biochim. Biophys. Acta 2005, 1708, 283-310], the entropy change (TDeltaS) is positive, +0.54 +/- 0.3 eV. The positive entropy contribution is larger than the positive enthalpy, which indicates that the A(-)F(X) to F(A/B)(-) step in photosystem I is entropy driven. Other possible contributions to the measured values are discussed.
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Affiliation(s)
- Harvey J.M. Hou
- Department of Chemistry, Gonzaga University, 502 E. Boone Avenue, Spokane, Washington 99258
| | - David Mauzerall
- The Rockefeller University, 1230 York Avenue, New York, New York 10021; Tel.: (212) 327-8218; Fax: (212) 327-8853;
- To whom correspondence should be addressed
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24
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Grabolle M, Dau H. Energetics of primary and secondary electron transfer in Photosystem II membrane particles of spinach revisited on basis of recombination-fluorescence measurements. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2005; 1708:209-18. [PMID: 15878422 DOI: 10.1016/j.bbabio.2005.03.007] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2004] [Revised: 03/14/2005] [Accepted: 03/15/2005] [Indexed: 10/25/2022]
Abstract
Photon absorption by one of the roughly 200 chlorophylls of the plant Photosystem II (PSII) results in formation of an equilibrated excited state (Chl200*) and is followed by chlorophyll oxidation (formation of P680+) coupled to reduction of a specific pheophytin (Phe), then electron transfer from Phe- to a firmly bound quinone (QA), and subsequently reduction of P680+ by a redox-active tyrosine residue denoted as Z. The involved free-energy differences (DeltaG) and redox potentials are of prime interest. Oxygen-evolving PSII membrane particles of spinach were studied at 5 degrees C. By analyzing the delayed and prompt Chl fluorescence, we determined the equilibrium constant and thus free-energy difference between Chl200* and the [Z+,QA-] radical pair to be -0.43+/-0.025 eV, at 10 mus after the photon absorption event for PSII in its S(3)-state. On basis of this value and previously published results, the free-energy difference between P680* and [P680+,QA-] is calculated to be -0.50+/-0.04 eV; the free-energy loss associated with electron transfer from Phe to QA is found to be 0.34+/-0.04 eV. The given uncertainty ranges do not represent a standard deviation or likely error, but an estimate of the maximal error. Assuming a QA-/QA redox potential of -0.08 V, the following redox-potential estimates are obtained: +1.25 V for P680/P680+; +1.21 V for Z/Z+ (at 10 mus); -0.42 V for Phe-/Phe; -0.58 V for P680*/P680+.
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Affiliation(s)
- Markus Grabolle
- Freie Universität Berlin, FB Physik Arnimallee 14, D-14195 Berlin, Germany
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25
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Vasil'ev S, Shen JR, Kamiya N, Bruce D. The orientations of core antenna chlorophylls in photosystem II are optimized to maximize the quantum yield of photosynthesis. FEBS Lett 2004; 561:111-6. [PMID: 15013760 DOI: 10.1016/s0014-5793(04)00133-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2004] [Revised: 01/19/2004] [Accepted: 01/20/2004] [Indexed: 10/26/2022]
Abstract
In photosystem II (PSII) the probability that energy absorbed by core antenna chlorophyll (Chl) is transferred to the reaction center (RC) is extremely high. Although close proximity between antenna Chl ensures a high transfer efficiency, relative pigment orientation can fractionally modify it. This level of refinement has often been assumed to be superfluous as so many subsequent processes limit the overall efficiency of photosynthesis. Nevertheless, did natural selection act on the most efficient step of energy conversion in PSII by optimizing the orientation of antenna Chl? Our Monte Carlo simulations sampled the orientation space of Chls in kinetic models for excitation energy transfer based on the X-ray structures of PSII from Thermosynechococcus vulcanus and Synechocystis elongatus. Our results revealed that the orientations of key antenna Chls are optimized to maximize photosynthesis while the orientations of the two peripheral RC Chls (Chl(Z)) are not.
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Affiliation(s)
- Sergei Vasil'ev
- Department of Biological Sciences, Brock University, St. Catharines, ON, Canada L2S 3A1.
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26
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Gensch T, Viappiani C. Time-resolved photothermal methods: accessing time-resolved thermodynamics of photoinduced processes in chemistry and biology. Photochem Photobiol Sci 2003; 2:699-721. [PMID: 12911218 DOI: 10.1039/b303177b] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Photothermal methods are currently being employed in a variety of research areas, ranging from materials science to environmental monitoring. Despite the common term which they are collected under, the implementations of these techniques are as diverse as the fields of application. In this review, we concentrate on the recent applications of time-resolved methods in photochemistry and photobiology.
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Affiliation(s)
- Thomas Gensch
- Forschungszentrum Jülich, Institut für Biologische Informationsverarbeitung 1, 52425 Jülich, Germany.
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27
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Losi A, Yruela I, Reus M, Holzwarth AR, Braslavsky SE. Structural changes upon excitation of D1-D2-Cyt b559 photosystem II reaction centers depend on the beta-carotene content. Photochem Photobiol Sci 2003; 2:722-9. [PMID: 12911219 DOI: 10.1039/b301282d] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Different preparations of D1-D2-Cyt b559 complexes from spinach with different beta-carotene (Car) content [on average from <0.5 to 2 per reaction center (RC)] were studied by means of laser-induced optoacoustic spectroscopy. phiP680(+)Pheo(-) does not depend on the preparation (or on the Car content) inasmuch as the magnitude of the prompt heat (produced within 20 ns) does not vary for the different samples upon excitation at 675 and 620 nm. The energy level of the primary charge-separated state, P680(+)Pheo(-), was determined as EP680(+)Pheo(-) = 1.55 eV. Thus, an enthalpy change accompanying charge separation from excited P680 of deltaH*P680Pheo-->P680(+)Pheo(-) = -0.27 eV is obtained. Calculations using the heat evolved during the time-resolved decay of P680(+)Pheo(-) (< or = 100 ns) affords a triplet (3[P680Pheo]) quantum yield phi3[P680Pheo] = 0.5 +/- 0.14. The structural volume change, deltaV1, corresponding to the formation of P680(+)Pheo(-), strongly depends on the Car content; it is ca. -2.5 A3 molecule(-1) for samples with <0.5 Car on average, decreases (in absolute value) to -0.5 +/- 0.2 A3 for samples with an average of 1 Car, and remains the same for samples with two Cars per RC. This suggests that the Car molecules induce changes in the ground-state RC conformation, an idea which was confirmed by preferential excitation of Car with blue light, which produced different carotene triplet lifetimes in samples with 2 Car compared to those containing less carotene. We conclude that the two beta-carotenes are not structurally equivalent. Upon blue-light excitation (480 nm, preferential carotene absorption) the fraction of energy stored is ca. 60% for the 9Chl-2Car sample, whereas it is 40% for the preparations with one or less Cars on average, indicating different paths of energy distribution after Car excitation in these RCs with remaining chlorophyll antennae.
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Affiliation(s)
- Aba Losi
- Max-Planck-Institut für Strahlenchemie, Postfach 10 13 65, 45413 Mülheim an der Ruhr, Germany
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28
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Mauzerall D, Liu Y, Edens GJ, Grzymski J. Measurement of enthalpy and volume changes in photoinitiated reactions on the ms timescale with a novel pressure cell. Photochem Photobiol Sci 2003; 2:788-90. [PMID: 12911228 DOI: 10.1039/b301448g] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Time-resolved photoacoustics is an excellent method with which to measure enthalpy and volume changes of photochemical and photobiological reactions. However, it fails at times longer than approximately 10 micros. The design principles of a pressure or volume cell covering the time range of 20 micros to several seconds is presented. The sensitivity of the cell has been verified and its application to the photocycle of bacteriorhodopsin is presented. Because of the similar cell structure and data analysis it is now possible to determine enthalpy and volume changes in photo-initiated reactions over the timescale of nanoseconds to seconds with the same solution.
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Affiliation(s)
- David Mauzerall
- The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
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30
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Losi A, Braslavsky SE. The time-resolved thermodynamics of the chromophore–protein interactions in biological photosensors as derived from photothermal measurements. Phys Chem Chem Phys 2003. [DOI: 10.1039/b303848c] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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