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Edge R, Truscott TG. Singlet Oxygen and Free Radical Reactions of Retinoids and Carotenoids-A Review. Antioxidants (Basel) 2018; 7:antiox7010005. [PMID: 29301252 PMCID: PMC5789315 DOI: 10.3390/antiox7010005] [Citation(s) in RCA: 82] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2017] [Revised: 12/11/2017] [Accepted: 12/29/2017] [Indexed: 12/29/2022] Open
Abstract
We report on studies of reactions of singlet oxygen with carotenoids and retinoids and a range of free radical studies on carotenoids and retinoids with emphasis on recent work, dietary carotenoids and the role of oxygen in biological processes. Many previous reviews are cited and updated together with new data not previously reviewed. The review does not deal with computational studies but the emphasis is on laboratory-based results. We contrast the ease of study of both singlet oxygen and polyene radical cations compared to neutral radicals. Of particular interest is the switch from anti- to pro-oxidant behavior of a carotenoid with change of oxygen concentration: results for lycopene in a cellular model system show total protection of the human cells studied at zero oxygen concentration, but zero protection at 100% oxygen concentration.
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Affiliation(s)
- Ruth Edge
- Dalton Cumbrian Facility, The University of Manchester, Westlakes Science and Technology Park, Moor Row, Cumbria CA24 3HA, UK.
| | - T George Truscott
- School of Chemical and Physical Sciences, Lennard-Jones Building, Keele University, Staffordshire ST5 5BG, UK.
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Photo Protection of Haematococcus pluvialis Algae by Astaxanthin: Unique Properties of Astaxanthin Deduced by EPR, Optical and Electrochemical Studies. Antioxidants (Basel) 2017; 6:antiox6040080. [PMID: 29065482 PMCID: PMC5745490 DOI: 10.3390/antiox6040080] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Revised: 10/17/2017] [Accepted: 10/18/2017] [Indexed: 01/30/2023] Open
Abstract
Abstract The antioxidant astaxanthin is known to accumulate in Haematococcus pluvialis algae under unfavorable environmental conditions for normal cell growth. The accumulated astaxanthin functions as a protective agent against oxidative stress damage, and tolerance to excessive reactive oxygen species (ROS) is greater in astaxanthin-rich cells. The detailed mechanisms of protection have remained elusive, however, our Electron Paramagnetic Resonance (EPR), optical and electrochemical studies on carotenoids suggest that astaxanthin's efficiency as a protective agent could be related to its ability to form chelate complexes with metals and to be esterified, its inability to aggregate in the ester form, its high oxidation potential and the ability to form proton loss neutral radicals under high illumination in the presence of metal ions. The neutral radical species formed by deprotonation of the radical cations can be very effective quenchers of the excited states of chlorophyll under high irradiation.
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Mukai K, Yoshimoto M, Ishikura M, Nagaoka SI. Kinetic Study of the Aroxyl-Radical-Scavenging Activity of Five Fatty Acid Esters and Six Carotenoids in Toluene Solution: Structure-Activity Relationship for the Hydrogen Abstraction Reaction. J Phys Chem B 2017; 121:7593-7601. [PMID: 28737395 DOI: 10.1021/acs.jpcb.7b04570] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A kinetic study of the reaction between an aroxyl radical (ArO•) and fatty acid esters (LHs 1-5, ethyl stearate 1, ethyl oleate 2, ethyl linoleate 3, ethyl linolenate 4, and ethyl arachidonate 5) has been undertaken. The second-order rate constants (ks) for the reaction of ArO• with LHs 1-5 in toluene at 25.0 °C have been determined spectrophotometrically. The ks values obtained increased in the order of LH 1 < 2 < 3 < 4 < 5, that is, with increasing the number of double bonds included in LHs 1-5. The ks value for LH 5 was 2.93 × 10-3 M-1 s-1. From the result, it has been clarified that the reaction of ArO• with LHs 1-5 was explained by an allylic hydrogen abstraction reaction. A similar kinetic study was performed for the reaction of ArO• with six carotenoids (Car-Hs 1-6, astaxanthin 1, β-carotene 2, lycopene 3, capsanthin 4, zeaxanthin 5, and lutein 6). The ks values obtained increased in the order of Car-H 1 < 2 < 3 < 4 < 5 < 6. The ks value for Car-H 6 was 8.4 × 10-4 M-1 s-1. The ks values obtained for Car-Hs 1-6 are in the same order as that of the values for LHs 1-5. The results of detailed analyses of the ks values for the above reaction indicated that the reaction was also explained by an allylic hydrogen abstraction reaction. Furthermore, the structure-activity relationship for the reaction was discussed by taking the result of density functional theory calculation reported by Martinez and Barbosa into account.
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Affiliation(s)
- Kazuo Mukai
- Department of Chemistry, Faculty of Science, Ehime University , Matsuyama 790-8577, Japan
| | - Maya Yoshimoto
- Department of Chemistry, Faculty of Science, Ehime University , Matsuyama 790-8577, Japan
| | - Masaharu Ishikura
- Green Project, Business Development Center, Showa Denko K.K. , Kawasaki 210-0858, Japan
| | - Shin-Ichi Nagaoka
- Department of Chemistry, Faculty of Science, Ehime University , Matsuyama 790-8577, Japan
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Radicals formed from proton loss of carotenoid radical cations: A special form of carotenoid neutral radical occurring in photoprotection. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2017; 166:148-157. [DOI: 10.1016/j.jphotobiol.2016.11.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Revised: 10/13/2016] [Accepted: 11/16/2016] [Indexed: 11/22/2022]
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Ligia Focsan A, Magyar A, Kispert LD. Chemistry of carotenoid neutral radicals. Arch Biochem Biophys 2015; 572:167-174. [DOI: 10.1016/j.abb.2015.02.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 02/03/2015] [Accepted: 02/04/2015] [Indexed: 10/24/2022]
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El-Agamey A, El-Hagrasy MA, Suenobu T, Fukuzumi S. Influence of pH on the decay of β-carotene radical cation in aqueous Triton X-100: A laser flash photolysis study. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2015; 146:68-73. [PMID: 25837728 DOI: 10.1016/j.jphotobiol.2015.02.026] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2014] [Revised: 02/17/2015] [Accepted: 02/19/2015] [Indexed: 11/25/2022]
Abstract
The identification of the spectral information of carotenoid neutral radicals is essential for studying their reactivities towards O2 and thereby evaluating their role in the antioxidant-prooxidant properties of the corresponding carotenoid. Recently, it was reported that β-carotene neutral radical (β-CAR) has an absorption maximum at 750 nm. This contradicts the results of many reports that show carotenoid neutral radicals (CAR) absorb in the same or near to the spectral region as their parent carotenoids. In this manuscript, the influence of pH on the decay of β-carotene radical cation (β-CAR-H(+)), generated in an aqueous solution of 2% Triton X-100 (TX-100), was investigated, employing laser flash photolysis (LFP) coupled with kinetic absorption spectroscopy, to identify the absorption bands of the β-carotene neutral radicals. By increasing the pH value of the solution, the decay of β-CAR-H(+) is enhanced and this enhancement is not associated with the formation of any positive absorption bands over the range 550-900 nm. By comparing these results with the literature, it can be concluded that β-carotene neutral radicals most probably absorb within the same spectral range as that of β-carotene. The reaction pathways of the reaction of β-CAR-H(+) with (-)OH have been discussed.
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Affiliation(s)
- Ali El-Agamey
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan; Chemistry Department, Faculty of Science, Damietta University, New Damietta, Damietta, Egypt
| | - Maha A El-Hagrasy
- Chemistry Department, Faculty of Science, Damietta University, New Damietta, Damietta, Egypt
| | - Tomoyoshi Suenobu
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan
| | - Shunichi Fukuzumi
- Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan
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Shinopoulos KE, Yu J, Nixon PJ, Brudvig GW. Using site-directed mutagenesis to probe the role of the D2 carotenoid in the secondary electron-transfer pathway of photosystem II. PHOTOSYNTHESIS RESEARCH 2014; 120:141-52. [PMID: 23334888 PMCID: PMC3961632 DOI: 10.1007/s11120-013-9793-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2012] [Accepted: 01/02/2013] [Indexed: 05/07/2023]
Abstract
Secondary electron transfer in photosystem II (PSII), which occurs when water oxidation is inhibited, involves redox-active carotenoids (Car), as well as chlorophylls (Chl), and cytochrome b 559 (Cyt b 559), and is believed to play a role in photoprotection. CarD2 may be the initial point of secondary electron transfer because it is the closest cofactor to both P680, the initial oxidant, and to Cyt b 559, the terminal secondary electron donor within PSII. In order to characterize the role of CarD2 and to determine the effects of perturbing CarD2 on both the electron-transfer events and on the identity of the redox-active cofactors, it is necessary to vary the properties of CarD2 selectively without affecting the ten other Car per PSII. To this end, site-directed mutations around the binding pocket of CarD2 (D2-G47W, D2-G47F, and D2-T50F) have been generated in Synechocystis sp. PCC 6803. Characterization by near-IR and EPR spectroscopy provides the first experimental evidence that CarD2 is one of the redox-active carotenoids in PSII. There is a specific perturbation of the Car(∙+) near-IR spectrum in all three mutated PSII samples, allowing the assignment of the spectral signature of Car D2 (∙+) ; Car D2 (∙+) exhibits a near-IR peak at 980 nm and is the predominant secondary donor oxidized in a charge separation at low temperature in ferricyanide-treated wild-type PSII. The yield of secondary donor radicals is substantially decreased in PSII complexes isolated from each mutant. In addition, the kinetics of radical formation are altered in the mutated PSII samples. These results are consistent with oxidation of CarD2 being the initial step in secondary electron transfer. Furthermore, normal light levels during mutant cell growth perturb the shape of the Chl(∙+) near-IR absorption peak and generate a dark-stable radical observable in the EPR spectra, indicating a higher susceptibility to photodamage further linking the secondary electron-transfer pathway to photoprotection.
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Affiliation(s)
| | - Jianfeng Yu
- Division of Molecular Biosciences, Sir Ernst Chain Building – Wolfson Laboratories, Imperial College London, S. Kensington campus, London, SW7 2AY UK
| | - Peter J. Nixon
- Division of Molecular Biosciences, Sir Ernst Chain Building – Wolfson Laboratories, Imperial College London, S. Kensington campus, London, SW7 2AY UK
| | - Gary W. Brudvig
- Department of Chemistry, Yale University, New Haven, CT 06520-8107 USA
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Álvarez R, Vaz B, Gronemeyer H, de Lera ÁR. Functions, therapeutic applications, and synthesis of retinoids and carotenoids. Chem Rev 2013; 114:1-125. [PMID: 24266866 DOI: 10.1021/cr400126u] [Citation(s) in RCA: 151] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Rosana Álvarez
- Departamento de Química Orgánica, Centro de Investigación Biomédica (CINBIO), and Instituto de Investigación Biomédica de Vigo (IBIV), Universidade de Vigo , 36310 Vigo, Spain
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Cerezo J, Zúñiga J, Bastida A, Requena A, Pedro Cerón-Carrasco J. Conformational changes of β-carotene and zeaxanthin immersed in a model membrane through atomistic molecular dynamics simulations. Phys Chem Chem Phys 2013; 15:6527-38. [DOI: 10.1039/c3cp43947j] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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Zaidi A, Li H, Sliwka HR, Partali V, Ernst H, Melø TB. Energy and electron transfer reactions of polyenic acids with variable chain lengths. Tetrahedron 2013. [DOI: 10.1016/j.tet.2012.10.041] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Cerezo J, Zúñiga J, Bastida A, Requena A, Cerón-Carrasco JP, Eriksson LA. Antioxidant Properties of β-Carotene Isomers and Their Role in Photosystems: Insights from Ab Initio Simulations. J Phys Chem A 2012; 116:3498-506. [DOI: 10.1021/jp301485k] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Javier Cerezo
- Departamento de Química Física, Universidad de Murcia, 30100 Murcia, Spain
| | - José Zúñiga
- Departamento de Química Física, Universidad de Murcia, 30100 Murcia, Spain
| | - Adolfo Bastida
- Departamento de Química Física, Universidad de Murcia, 30100 Murcia, Spain
| | - Alberto Requena
- Departamento de Química Física, Universidad de Murcia, 30100 Murcia, Spain
| | - José Pedro Cerón-Carrasco
- CEISAM, UMR CNRS 6230, BP 92208, Université de Nantes, 2, rue de la Houssinière, 44322 Nantes
Cedex 3, France
| | - Leif A. Eriksson
- Department of Chemistry and Molecular Biology, University of Gothenburg, 41296 Göteborg, Sweden
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Shinopoulos KE, Brudvig GW. Cytochrome b₅₅₉ and cyclic electron transfer within photosystem II. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2011; 1817:66-75. [PMID: 21864501 DOI: 10.1016/j.bbabio.2011.08.002] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2011] [Revised: 08/06/2011] [Accepted: 08/08/2011] [Indexed: 11/18/2022]
Abstract
Cytochrome b₅₅₉ (Cyt b₅₅₉), β-carotene (Car), and chlorophyll (Chl) cofactors participate in the secondary electron-transfer pathways in photosystem II (PSII), which are believed to protect PSII from photodamage under conditions in which the primary electron-donation pathway leading to water oxidation is inhibited. Among these cofactors, Cyt b₅₅₉ is preferentially photooxidized under conditions in which the primary electron-donation pathway is blocked. When Cyt b₅₅₉ is preoxidized, the photooxidation of several of the 11 Car and 35 Chl molecules present per PSII is observed. In this review, the discovery of the secondary electron donors, their structures and electron-transfer properties, and progress in the characterization of the secondary electron-transfer pathways are discussed. This article is part of a Special Issue entitled: Photosystem II.
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Focsan AL, Bowman MK, Molnár P, Deli J, Kispert LD. Carotenoid radical formation: dependence on conjugation length. J Phys Chem B 2011; 115:9495-506. [PMID: 21711000 DOI: 10.1021/jp204787b] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The relative energy of carotenoid neutral radicals formed by proton loss from the radical cations of linear carotenoids has been examined as a function of conjugation length from n = 15 to 9. For a maximum conjugation length of n = 15 (bisdehydrolycopene, a symmetrical compound), proton loss can occur from any of the 10 methyl groups, with proton loss from the methyl group at position C1 or C1' being the most favorable. In contrast, the most energetically favorable proton loss from the radical cations of lycopene, neurosporene, spheroidene, spheroidenone, spirilloxanthin, and anhydrorhodovibrin occurs from methylene groups that extend from the conjugated system. For example, decreasing the conjugation length to n = 11 (lycopene) by saturation of the double bonds C3-C4 and at C3'-C4' of bisdehydrolycopene favors proton loss at C4 or C4' methylene groups. Saturation at C7'-C8' in the case of neurosporene, spheroidene, and spheroidenone (n = 9, 10, 11) favors the formation of a neutral radical at the C8' methylene group. Saturation of C1-C2 by addition of a methoxy group to a bisdehydrolycopene-like structure with conjugation of n = 12 or 13 (anhydrorhodovibrin, spirilloxanthin) favors proton loss at the C2 methylene group. As a consequence of deprotonation of the radical cation, the unpaired electron spin distribution changes so that larger β-methyl proton couplings occur for the neutral radicals (13-16 MHz) than for the radical cation (7-10 MHz), providing a means to identify possible carotenoid radicals in biological systems by Mims ENDOR.
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Affiliation(s)
- A Ligia Focsan
- Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama 35487-0336, United States
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El-Agamey A, Fukuzumi S. Laser flash photolysis study on the retinol radical cation in polar solvents. Org Biomol Chem 2011; 9:6437-46. [DOI: 10.1039/c1ob05814b] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
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Pang Y, Jones GA, Prantil MA, Fleming GR. Unusual Relaxation Pathway from the Two-Photon Excited First Singlet State of Carotenoids. J Am Chem Soc 2010; 132:2264-73. [DOI: 10.1021/ja908472y] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Yoonsoo Pang
- Department of Chemistry, University of California, Berkeley, and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-1460
| | - Garth A. Jones
- Department of Chemistry, University of California, Berkeley, and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-1460
| | - Matthew A. Prantil
- Department of Chemistry, University of California, Berkeley, and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-1460
| | - Graham R. Fleming
- Department of Chemistry, University of California, Berkeley, and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-1460
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Polyakov NE, Leshina TV, Meteleva ES, Dushkin AV, Konovalova TA, Kispert LD. Enhancement of the photocatalytic activity of TiO2 nanoparticles by water-soluble complexes of carotenoids. J Phys Chem B 2009; 114:14200-4. [PMID: 19968316 DOI: 10.1021/jp908578j] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Photoirradiation of TiO(2) nanoparticles by visible light in the presence of the water-soluble natural polysaccharide arabinogalactan complexes of the hydrocarbon carotenoid β-carotene leads to enhanced yield of the reactive hydroxyl (OH) radicals. The electron paramagnetic resonance (EPR) spin-trapping technique using α-phenyl-N-tert-butyl nitrone (PBN) as the spin-trap has been applied to detect this intermediate by trapping the methyl and methoxy radicals generated upon reaction of the hydroxyl radical with dimethylsulfoxide (DMSO). The free radicals formed in this system proceed via oxygen reduction and not via the reaction of holes on the TiO(2) surface. As compared with pure carotenoids, carotenoid-arabinogalactan complexes exhibit an enhanced quantum yield of free radicals and stability toward photodegradation. The observed enhancement of the photocatalytic efficiency for carotenoid complexes, as measured by the quantum yield of the desired spin adducts, arises specifically from the decrease in the rate constant for the back electron transfer to the carotenoid radical cation. These results are important for a variety of TiO(2) applications, namely, in photodynamic therapy, and in the design of artificial light-harvesting, photoredox, and catalytic devices.
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Tracewell CA, Brudvig GW. Multiple redox-active chlorophylls in the secondary electron-transfer pathways of oxygen-evolving photosystem II. Biochemistry 2008; 47:11559-72. [PMID: 18850718 PMCID: PMC2674297 DOI: 10.1021/bi801461d] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Photosystem II (PS II) is unique among photosynthetic reaction centers in having secondary electron donors that compete with the primary electron donors for reduction of P680(+). We have characterized the photooxidation and dark decay of the redox-active accessory chlorophylls (Chl) and beta-carotenes (Car) in oxygen-evolving PS II core complexes by near-IR absorbance and EPR spectroscopies at cryogenic temperatures. In contrast to previous results for Mn-depleted PS II, multiple near-IR absorption bands are resolved in the light-minus-dark difference spectra of oxygen-evolving PS II core complexes including two fast-decaying bands at 793 and 814 nm and three slow-decaying bands at 810, 825, and 840 nm. We assign these bands to chlorophyll cation radicals (Chl(+)). The fast-decaying bands observed after illumination at 20 K could be generated again by reilluminating the sample. Quantization by EPR gives a yield of 0.85 radicals per PS II, and the yield of oxidized cytochrome b 559 by optical difference spectroscopy is 0.15 per PS II. Potential locations of Chl(+) and Car(+) species, and the pathways of secondary electron transfer based on the rates of their formation and decay, are discussed. This is the first evidence that Chls in the light-harvesting proteins CP43 and CP47 are oxidized by P680(+) and may have a role in Chl fluorescence quenching. We also suggest that a possible role for negatively charged lipids (phosphatidyldiacylglycerol and sulfoquinovosyldiacylglycerol identified in the PS II structure) could be to decrease the redox potential of specific Chl and Car cofactors. These results provide new insight into the alternate electron-donation pathways to P680(+).
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Affiliation(s)
| | - Gary W. Brudvig
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520-8107, U.S.A
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Tracewell CA, Brudvig GW. Characterization of the secondary electron-transfer pathway intermediates of photosystem II containing low-potential cytochrome b559. PHOTOSYNTHESIS RESEARCH 2008; 98:189-97. [PMID: 18780156 DOI: 10.1007/s11120-008-9360-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2008] [Accepted: 08/19/2008] [Indexed: 05/09/2023]
Abstract
Beta-carotene (Car) and chlorophyll (Chl) function as secondary electron donors in photosystem II (PS II) under conditions, such as low temperature, when electron donation from the O(2)-evolving complex is inhibited. In prior studies of the formation and decay of Car(*+) and Chl(*+) species at low temperatures, cytochrome b(559) (Cyt b(559)) was chemically oxidized prior to freezing the sample. In this study, the photochemical formation of Car(*+) and Chl(*+) is characterized at low temperature in O(2)-evolving Synechocystis PS II treated with ascorbate to reduce most of the Cyt b(559). Not all of the Cyt b(559) is reduced by ascorbate; the remainder of the PS II reaction centers, containing oxidized low-potential Cyt b(559), give rise to Car(*+) and Chl(*+) species after illumination at low temperature that are characterized by near-IR spectroscopy. These data are compared to the measurements on ferricyanide-treated O(2)-evolving Synechocystis PS II in which the Car(*+) and Chl(*+) species are generated in PS II centers containing mostly high- and intermediate-potential Cyt b(559). Spectral differences observed in the ascorbate-reduced PS II samples include decreased intensity of the Chl(*+) and Car(*+) absorbance peaks, shifts in the Car(*+) absorbance maxima, and lack of formation of a 750 nm species that is assigned to a Car neutral radical. These results suggest that different spectral forms of Car are oxidized in PS II samples containing different redox forms of Cyt b(559), which implies that different secondary electron donors are favored depending on the redox form of Cytb(559) in PS II.
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Affiliation(s)
- Cara A Tracewell
- Department of Chemistry, Yale University, New Haven, CT 06520-8107, USA
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