1
|
Kobayashi Y, Fukuda D, Okayasu Y, Nagai Y. Relaxation dynamics of higher excited states of perylene-substituted perylene bisimide derivatives. J Chem Phys 2024; 161:034308. [PMID: 39017426 DOI: 10.1063/5.0205882] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2024] [Accepted: 06/28/2024] [Indexed: 07/18/2024] Open
Abstract
Stepwise two-photon absorption processes have received considerable attention, especially in photocatalysis, due to their relatively lower power threshold, characteristic spatial selectivity, amplification of chemical reactions, and so on. Meanwhile, studies on the relaxation dynamics of higher excited states in condensed systems have been limited for several molecular systems due to the short-lived nature of these states. In this study, we synthesized perylene-substituted perylene bisimide (PBI) and its derivate as model compounds and investigated their excited-state dynamics, including higher excited states, using pump-repump-probe spectroscopy. We revealed that these molecules form charge-transfer (CT) states instantaneously after the excitation, regardless of whether it is the perylene moiety or the PBI moiety that is excited. The lifetime of the CT state was shorter when the distance between the donor (perylene) and the acceptor (PBI) was shorter. Moreover, we also revealed that a higher-lying CT state generated by the stepwise excitation of the CT state using a 740-nm pulse induced Stark effect to the neighboring perylene moiety. The Stark effect not only gives more detailed information about the CT state, but also presents the possibility of new photofunctions, such as instantaneous modulation of the electronic state to achieve optimal electronic properties. These insights contribute to understanding advanced photochemical reactions and would be important for exploring photocatalytic reactions involving higher excited states.
Collapse
Affiliation(s)
- Yoichi Kobayashi
- Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan
| | - Daiki Fukuda
- Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan
| | - Yoshinori Okayasu
- Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan
| | - Yuki Nagai
- Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan
| |
Collapse
|
2
|
Zazubovich V, Jankowiak R. High-Resolution Frequency-Domain Spectroscopic and Modeling Studies of Photosystem I (PSI), PSI Mutants and PSI Supercomplexes. Int J Mol Sci 2024; 25:3850. [PMID: 38612659 PMCID: PMC11011720 DOI: 10.3390/ijms25073850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2024] [Revised: 03/23/2024] [Accepted: 03/26/2024] [Indexed: 04/14/2024] Open
Abstract
Photosystem I (PSI) is one of the two main pigment-protein complexes where the primary steps of oxygenic photosynthesis take place. This review describes low-temperature frequency-domain experiments (absorption, emission, circular dichroism, resonant and non-resonant hole-burned spectra) and modeling efforts reported for PSI in recent years. In particular, we focus on the spectral hole-burning studies, which are not as common in photosynthesis research as the time-domain spectroscopies. Experimental and modeling data obtained for trimeric cyanobacterial Photosystem I (PSI3), PSI3 mutants, and PSI3-IsiA18 supercomplexes are analyzed to provide a more comprehensive understanding of their excitonic structure and excitation energy transfer (EET) processes. Detailed information on the excitonic structure of photosynthetic complexes is essential to determine the structure-function relationship. We will focus on the so-called "red antenna states" of cyanobacterial PSI, as these states play an important role in photochemical processes and EET pathways. The high-resolution data and modeling studies presented here provide additional information on the energetics of the lowest energy states and their chlorophyll (Chl) compositions, as well as the EET pathways and how they are altered by mutations. We present evidence that the low-energy traps observed in PSI are excitonically coupled states with significant charge-transfer (CT) character. The analysis presented for various optical spectra of PSI3 and PSI3-IsiA18 supercomplexes allowed us to make inferences about EET from the IsiA18 ring to the PSI3 core and demonstrate that the number of entry points varies between sample preparations studied by different groups. In our most recent samples, there most likely are three entry points for EET from the IsiA18 ring per the PSI core monomer, with two of these entry points likely being located next to each other. Therefore, there are nine entry points from the IsiA18 ring to the PSI3 trimer. We anticipate that the data discussed below will stimulate further research in this area, providing even more insight into the structure-based models of these important cyanobacterial photosystems.
Collapse
Affiliation(s)
- Valter Zazubovich
- Department of Physics, Concordia University, Montreal, QC H4B 1R6, Canada
| | - Ryszard Jankowiak
- Department of Chemistry, Kansas State University, Manhattan, KS 66506, USA
| |
Collapse
|
3
|
Cherepanov DA, Semenov AY, Mamedov MD, Aybush AV, Gostev FE, Shelaev IV, Shuvalov VA, Nadtochenko VA. Current state of the primary charge separation mechanism in photosystem I of cyanobacteria. Biophys Rev 2022; 14:805-820. [PMID: 36124265 PMCID: PMC9481807 DOI: 10.1007/s12551-022-00983-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Accepted: 07/10/2022] [Indexed: 11/24/2022] Open
Abstract
This review analyzes new data on the mechanism of ultrafast reactions of primary charge separation in photosystem I (PS I) of cyanobacteria obtained in the last decade by methods of femtosecond absorption spectroscopy. Cyanobacterial PS I from many species harbours 96 chlorophyll a (Chl a) molecules, including six specialized Chls denoted Chl1A/Chl1B (dimer P700, or PAPB), Chl2A/Chl2B, and Chl3A/Chl3B arranged in two branches, which participate in electron transfer reactions. The current data indicate that the primary charge separation occurs in a symmetric exciplex, where the special pair P700 is electronically coupled to the symmetrically located monomers Chl2A and Chl2B, which can be considered together as a symmetric exciplex Chl2APAPBChl2B with the mixed excited (Chl2APAPBChl2B)* and two charge-transfer states P700 +Chl2A - and P700 +Chl2B -. The redistribution of electrons between the branches in favor of the A-branch occurs after reduction of the Chl2A and Chl2B monomers. The formation of charge-transfer states and the symmetry breaking mechanisms were clarified by measuring the electrochromic Stark shift of β-carotene and the absorption dynamics of PS I complexes with the genetically altered Chl 2B or Chl 2A monomers. The review gives a brief description of the main methods for analyzing data obtained using femtosecond absorption spectroscopy. The energy levels of excited and charge-transfer intermediates arising in the cyanobacterial PS I are critically analyzed.
Collapse
Affiliation(s)
- Dmitry A. Cherepanov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 119991, Kosygina Street 1, Moscow, Russia
| | - Alexey Yu Semenov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 119991, Kosygina Street 1, Moscow, Russia
- A.N. Belozersky Institute of Physical-Chemical Biology, M.V. Lomonosov Moscow State University, 119992 Leninskye gory 1 building, 40 Moscow, Russia
| | - Mahir D. Mamedov
- A.N. Belozersky Institute of Physical-Chemical Biology, M.V. Lomonosov Moscow State University, 119992 Leninskye gory 1 building, 40 Moscow, Russia
| | - Arseniy V. Aybush
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 119991, Kosygina Street 1, Moscow, Russia
| | - Fedor E. Gostev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 119991, Kosygina Street 1, Moscow, Russia
| | - Ivan V. Shelaev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 119991, Kosygina Street 1, Moscow, Russia
| | - Vladimir A. Shuvalov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 119991, Kosygina Street 1, Moscow, Russia
| | - Victor A. Nadtochenko
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 119991, Kosygina Street 1, Moscow, Russia
- Department of Chemistry, Lomonosov Moscow State University, 119991, Leninskiye Gory 1-3, Moscow, Russia
| |
Collapse
|
4
|
Cherepanov DA, Shelaev IV, Gostev FE, Nadtochenko VA, Xu W, Golbeck JH, Semenov AY. Symmetry breaking in photosystem I: ultrafast optical studies of variants near the accessory chlorophylls in the A- and B-branches of electron transfer cofactors. Photochem Photobiol Sci 2021; 20:1209-1227. [PMID: 34478050 DOI: 10.1007/s43630-021-00094-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Accepted: 08/18/2021] [Indexed: 11/25/2022]
Abstract
Femtosecond absorption spectroscopy of Photosystem I (PS I) complexes from the cyanobacterium Synechocystis sp. PCC 6803 was carried out on three pairs of complementary amino acid substitutions located near the second pair of chlorophyll molecules Chl2A and Chl2B (also termed A-1A and A-1B). The absorption dynamics at delays of 0.1-500 ps were analyzed by decomposition into discrete decay-associated spectra and continuously distributed exponential components. The multi-exponential deconvolution of the absorption changes revealed that the electron transfer reactions in the PsaA-N600M, PsaA-N600H, and PsaA-N600L variants near the B-branch of cofactors are similar to those of the wild type, while the PsaB-N582M, PsaB-N582H, and PsaB-N582L variants near the A-branch of cofactors cause significant alterations of the photochemical processes, making them heterogeneous and poorly described by a discrete exponential kinetic model. A redistribution of the unpaired electron between the second and the third monomers Chl2A/Chl2B and Chl3A/Chl3B was identified in the time range of 9-20 ps, and the subsequent reduction of A1 was identified in the time range of 24-70 ps. In the PsaA-N600L and PsaB-N582H/L variants, the reduction of A1 occurred with a decreased quantum yield of charge separation. The decreased quantum yield correlates with a slowing of the phylloquinone A0 → A1 reduction, but not with the initial transient spectra measured at the shortest time delay. The results support a branch competition model, where the electron is sheared between Chl2A-Chl3A and Chl2B-Chl3B cofactors before its transfer to phylloquinone in either A1A or A1B sites.
Collapse
Affiliation(s)
- Dmitry A Cherepanov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygina St. 4, Moscow, 117977, Russian Federation.
| | - Ivan V Shelaev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygina St. 4, Moscow, 117977, Russian Federation
| | - Fedor E Gostev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygina St. 4, Moscow, 117977, Russian Federation
| | - Victor A Nadtochenko
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygina St. 4, Moscow, 117977, Russian Federation.,Department of Chemistry, Lomonosov Moscow State University, Leninskiye Gory 1-3, Moscow, 119991, Russian Federation
| | - Wu Xu
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, LA, 70504, USA
| | - John H Golbeck
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16801, USA.,Department of Chemistry, The Pennsylvania State University, University Park, PA, 16801, USA
| | - Alexey Yu Semenov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygina St. 4, Moscow, 117977, Russian Federation.,A.N. Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 1, Moscow, 119992, Russian Federation
| |
Collapse
|
5
|
Cherepanov DA, Shelaev IV, Gostev FE, Petrova A, Aybush AV, Nadtochenko VA, Xu W, Golbeck JH, Semenov AY. Primary charge separation within the structurally symmetric tetrameric Chl 2AP AP BChl 2B chlorophyll exciplex in photosystem I. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2021; 217:112154. [PMID: 33636482 DOI: 10.1016/j.jphotobiol.2021.112154] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Revised: 01/05/2021] [Accepted: 02/12/2021] [Indexed: 12/01/2022]
Abstract
In Photosystem I (PS I), the role of the accessory chlorophyll (Chl) molecules, Chl2A and Chl2B (also termed A-1A and A-1B), which are directly adjacent to the special pair P700 and fork into the A- and B-branches of electron carriers, is incompletely understood. In this work, the Chl2A and Chl2B transient absorption ΔA0(λ) at a time delay of 100 fs was identified by ultrafast pump-probe spectroscopy in three pairs of PS I complexes from Synechocystis sp. PCC 6803 with residues PsaA-N600 or PsaB-N582 (which ligate Chl2B or Chl2A through a H2O molecule) substituted by Met, His, and Leu. The ΔA0(λ) spectra were quantified using principal component analysis, the main component of which was interpreted as a mutation-induced shift of the equilibrium between the excited state of primary donor P700⁎ and the primary charge-separated state P700+Chl2-. This equilibrium is shifted to the charge-separated state in wild-type PS I and to the excited P700 in the PS I complexes with the substituted ligands to the Chl2A and Chl2B monomers. The results can be rationalized within the framework of an adiabatic model in which the P700 is electronically coupled with the symmetrically arranged monomers Chl2A and Chl2B; such a structure can be considered a symmetric tetrameric exciplex Chl2APAPBChl2B, in which the excited state (Chl2APAPBChl2B)* is mixed with two charge-transfer states P700+Chl2A- and P700+Chl2B-. The electron redistribution between the two branches in favor of the A-branch apparently takes place in the picosecond time scale after reduction of the Chl2A and Chl2B monomers.
Collapse
Affiliation(s)
- Dmitry A Cherepanov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia.
| | - Ivan V Shelaev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia
| | - Fedor E Gostev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia
| | - Anastasia Petrova
- A.N. Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Leninskie gory, 1, Building 40, Russia
| | - Arseniy V Aybush
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia
| | - Victor A Nadtochenko
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia; Department of Chemistry, Lomonosov Moscow State University, Leninskiye Gory 1-3, Moscow 119991, Russian Federation
| | - Wu Xu
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, LA 70504, USA
| | - John H Golbeck
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16801, USA; Department of Chemistry, The Pennsylvania State University, University Park, PA 16801, USA
| | - Alexey Yu Semenov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia; A.N. Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Leninskie gory, 1, Building 40, Russia
| |
Collapse
|
6
|
Cherepanov DA, Shelaev IV, Gostev FE, Aybush AV, Mamedov MD, Shuvalov VA, Semenov AY, Nadtochenko VA. Generation of ion-radical chlorophyll states in the light-harvesting antenna and the reaction center of cyanobacterial photosystem I. PHOTOSYNTHESIS RESEARCH 2020; 146:55-73. [PMID: 32144697 DOI: 10.1007/s11120-020-00731-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Accepted: 02/24/2020] [Indexed: 05/09/2023]
Abstract
The energy and charge-transfer processes in photosystem I (PS I) complexes isolated from cyanobacteria Thermosynechococcus elongatus and Synechocystis sp. PCC 6803 were investigated by pump-to-probe femtosecond spectroscopy. The formation of charge-transfer (CT) states in excitonically coupled chlorophyll a complexes (exciplexes) was monitored by measuring the electrochromic shift of β-carotene in the spectral range 500-510 nm. The excitation of high-energy chlorophyll in light-harvesting antenna of both species was not accompanied by immediate appearance of an electrochromic shift. In PS I from T. elongatus, the excitation of long-wavelength chlorophyll (LWC) caused a pronounced electrochromic effect at 502 nm assigned to the appearance of CT states of chlorophyll exciplexes. The formation of ion-radical pair P700+A1- at 40 ps was limited by energy transfer from LWC to the primary donor P700 and accompanied by carotenoid bleach at 498 nm. In PS I from Synechocystis 6803, the excitation at 720 nm produced an immediate bidentate bleach at 690/704 nm and synchronous carotenoid response at 508 nm. The bidentate bleach was assigned to the formation of primary ion-radical state PB+Chl2B-, where negative charge is localized predominantly at the accessory chlorophyll molecule in the branch B, Chl2B. The following decrease of carotenoid signal at ~ 5 ps was ascribed to electron transfer to the more distant molecule Chl3B. The reduction of phylloquinone in the sites A1A and A1B was accompanied by a synchronous blue-shift of the carotenoid response to 498 nm, pointing to fast redistribution of unpaired electron between two branches in favor of the state PB+A1A-.
Collapse
Affiliation(s)
- Dmitry A Cherepanov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia.
| | - Ivan V Shelaev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia
| | - Fedor E Gostev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia
| | - Arseniy V Aybush
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia
| | - Mahir D Mamedov
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Kosygina st., 4, Moscow, Russia, 117991
| | - Vladimir A Shuvalov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Kosygina st., 4, Moscow, Russia, 117991
- Institute of Basic Biological Problems, Pushchino Scientific Center for Biological Research, Russian Academy of Sciences, Pushchino, Moscow Region, Russia
| | - Alexey Yu Semenov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Kosygina st., 4, Moscow, Russia, 117991
| | - Victor A Nadtochenko
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia
| |
Collapse
|
7
|
Fare C, Yuan L, Cordon-Preciado V, Michels JJ, Bearpark MJ, Rich P, van Thor JJ. Radical-Triggered Reaction Mechanism of the Green-to-Red Photoconversion of EosFP. J Phys Chem B 2020; 124:7765-7778. [PMID: 32805110 DOI: 10.1021/acs.jpcb.0c04587] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Reaction intermediates in the green-to-red photoconversion of the photochromic fluorescent protein EosFP have been observed using high-intensity continuous blue illumination. An intermediate was identified through light-induced accumulation that continues to convert the green form in subsequent darkness, putatively containing a tyrosyl radical, albeit with anomalously shifted features in both the electronic and FTIR spectra. Lowering the pH to 5.5 significantly delays the decay of this tyrosyl intermediate, which is accompanied by Stark-shifted features in the electronic spectra of reactants and products. Vibrational mode assignments for the high-frequency and fingerprint FTIR spectral regions of the reaction intermediates support a proposed sequence of events where the newly formed Cα═Cβ ethylenic bond precedes modifications on the His-62 imidazole ring and confirms a C═O(NH2) product group on Phe-61. We propose a reaction mechanism that involves tyrosyl generation via singlet excited-state-mediated oxidation which subsequently triggers the covalent reactions by oxidation of the green chromophore.
Collapse
Affiliation(s)
- Clyde Fare
- Molecular Biophysics, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom.,Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, 80 Wood Lane, London SW7 2AZ, United Kingdom
| | - Letong Yuan
- Molecular Biophysics, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
| | - Violeta Cordon-Preciado
- Molecular Biophysics, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
| | - Jasper J Michels
- Division of Molecular Electronics, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Michael J Bearpark
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, 80 Wood Lane, London SW7 2AZ, United Kingdom
| | - Peter Rich
- Department of Structural and Molecular Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Jasper J van Thor
- Molecular Biophysics, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
| |
Collapse
|
8
|
Khmelnitskiy A, Toporik H, Mazor Y, Jankowiak R. On the Red Antenna States of Photosystem I Mutants from Cyanobacteria Synechocystis PCC 6803. J Phys Chem B 2020; 124:8504-8515. [DOI: 10.1021/acs.jpcb.0c05201] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Anton Khmelnitskiy
- Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
| | - Hila Toporik
- School of Molecular Sciences and The Biodesign Institute, Arizona State University, Tempe, Arizona 85287, United States
| | - Yuval Mazor
- School of Molecular Sciences and The Biodesign Institute, Arizona State University, Tempe, Arizona 85287, United States
| | - Ryszard Jankowiak
- Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
- Department of Physics, Kansas State University, Manhattan, Kansas 66506, United States
| |
Collapse
|
9
|
Evidence that chlorophyll f functions solely as an antenna pigment in far-red-light photosystem I from Fischerella thermalis PCC 7521. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2020; 1861:148184. [PMID: 32179058 DOI: 10.1016/j.bbabio.2020.148184] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Revised: 02/21/2020] [Accepted: 03/09/2020] [Indexed: 11/20/2022]
Abstract
The Photosystem I (PSI) reaction center in cyanobacteria is comprised of ~96 chlorophyll (Chl) molecules, including six specialized Chl molecules denoted Chl1A/Chl1B (P700), Chl2A/Chl2B, and Chl3A/Chl3B that are arranged in two branches and function in primary charge separation. It has recently been proposed that PSI from Chroococcidiopsis thermalis (Nürnberg et al. (2018) Science 360, 1210-1213) and Fischerella thermalis PCC 7521 (Hastings et al. (2019) Biochim. Biophys. Acta 1860, 452-460) contain Chl f in the positions Chl2A/Chl2B. We tested this proposal by exciting RCs from white-light grown (WL-PSI) and far-red light grown (FRL-PSI) F. thermalis PCC 7521 with femtosecond pulses and analyzing the optical dynamics. If Chl f were in the position Chl2A/Chl2B in FRL-PSI, excitation at 740 nm should have produced the charge-separated state P700+A0- followed by electron transfer to A1 with a τ of ≤25 ps. Instead, it takes ~230 ps for the charge-separated state to develop because the excitation migrates uphill from Chl f in the antenna to the trapping center. Further, we observe a strong electrochromic shift at 685 nm in the final P700+A1- spectrum that can only be explained if Chl a is in the positions Chl2A/Chl2B. Similar arguments rule out the presence of Chl f in the positions Chl3A/Chl3B; hence, Chl f is likely to function solely as an antenna pigment in FRL-PSI. We additionally report the presence of an excitonically coupled homo- or heterodimer of Chl f absorbing around 790 nm that is kinetically independent of the Chl f population that absorbs around 740 nm.
Collapse
|
10
|
Cherepanov DA, Brady NG, Shelaev IV, Nguyen J, Gostev FE, Mamedov MD, Nadtochenko VA, Bruce BD. PSI-SMALP, a Detergent-free Cyanobacterial Photosystem I, Reveals Faster Femtosecond Photochemistry. Biophys J 2020; 118:337-351. [PMID: 31882247 PMCID: PMC6976803 DOI: 10.1016/j.bpj.2019.11.3391] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 11/17/2019] [Accepted: 11/26/2019] [Indexed: 12/12/2022] Open
Abstract
Cyanobacterial photosystem I (PSI) functions as a light-driven cyt c6-ferredoxin/oxidoreductase located in the thylakoid membrane. In this work, the energy and charge transfer processes in PSI complexes isolated from Thermosynechococcus elongatus via conventional n-dodecyl-β-D-maltoside solubilization (DM-PSI) and a, to our knowledge, new detergent-free method using styrene-maleic acid copolymers (SMA-PSI) have been investigated by pump-to-probe femtosecond laser spectroscopy. In DM-PSI preparations excited at 740 nm, the excitation remained localized on the long-wavelength chlorophyll forms within 0.1-20 ps and revealed little or no charge separation and oxidation of the special pair, P700. The formation of ion-radical pair P700+A1- occurred with a characteristic time of 36 ps, being kinetically controlled by energy transfer from the long-wavelength chlorophyll to P700. Quite surprisingly, the detergent-free SMA-PSI complexes upon excitation by these long-wave pulses undergo an ultrafast (<100 fs) charge separation in ∼45% of particles. In the remaining complexes (∼55%), the energy transfer to P700 occurred at ∼36 ps, similar to the DM-PSI. Both isolation methods result in a trimeric form of PSI, yet the SMA-PSI complexes display a heterogenous kinetic behavior. The much faster rate of charge separation suggests the existence of an ultrafast pathway for charge separation in the SMA-PSI that may be disrupted during detergent isolation.
Collapse
Affiliation(s)
- Dmitry A Cherepanov
- N. N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia
| | - Nathan G Brady
- Biochemistry and Cellular and Molecular Biology Department, University of Tennessee, Knoxville, Tennessee
| | - Ivan V Shelaev
- N. N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia
| | - Jon Nguyen
- Biochemistry and Cellular and Molecular Biology Department, University of Tennessee, Knoxville, Tennessee
| | - Fedor E Gostev
- N. N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia
| | - Mahir D Mamedov
- A. N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Moscow, Russia
| | - Victor A Nadtochenko
- N. N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia.
| | - Barry D Bruce
- Biochemistry and Cellular and Molecular Biology Department, University of Tennessee, Knoxville, Tennessee; Energy Science & Engineering Program, The Bredesen Center, University of Tennessee, Knoxville, Tennessee.
| |
Collapse
|
11
|
Bhaduri S, Stadnytskyi V, Zakharov SD, Hasan SS, Bujnowicz Ł, Sarewicz M, Savikhin S, Osyczka A, Cramer WA. Pathways of Transmembrane Electron Transfer in Cytochrome bc Complexes: Dielectric Heterogeneity and Interheme Coulombic Interactions. J Phys Chem B 2017; 121:975-983. [DOI: 10.1021/acs.jpcb.6b11709] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
| | | | | | | | - Ł. Bujnowicz
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics, and
Biotechnology, Jagiellonian University, Kraków 31-007, Poland
| | - M. Sarewicz
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics, and
Biotechnology, Jagiellonian University, Kraków 31-007, Poland
| | | | - A. Osyczka
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics, and
Biotechnology, Jagiellonian University, Kraków 31-007, Poland
| | | |
Collapse
|
12
|
Kaucikas M, Nürnberg D, Dorlhiac G, Rutherford AW, van Thor JJ. Femtosecond Visible Transient Absorption Spectroscopy of Chlorophyll f-Containing Photosystem I. Biophys J 2017; 112:234-249. [PMID: 28122212 PMCID: PMC5266252 DOI: 10.1016/j.bpj.2016.12.022] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2016] [Revised: 11/02/2016] [Accepted: 12/01/2016] [Indexed: 01/09/2023] Open
Abstract
Photosystem I (PSI) from Chroococcidiopsis thermalis PCC 7203 grown under far-red light (FRL; >725 nm) contains both chlorophyll a and a small proportion of chlorophyll f. Here, we investigated excitation energy transfer and charge separation using this FRL-grown form of PSI (FRL-PSI). We compared femtosecond transient visible absorption changes of normal, white-light (WL)-grown PSI (WL-PSI) with those of FRL-PSI using excitation at 670 nm, 700 nm, and (in the case of FRL-PSI) 740 nm. The possibility that chlorophyll f participates in energy transfer or charge separation is discussed on the basis of spectral assignments. With selective pumping of chlorophyll f at 740 nm, we observe a final ∼150 ps decay assigned to trapping by charge separation, and the amplitude of the resulting P700+•A1-• charge-separated state indicates that the yield is directly comparable to that of WL-PSI. The kinetics shows a rapid 2 ps time constant for almost complete transfer to chlorophyll f if chlorophyll a is pumped with a wavelength of 670 nm or 700 nm. Although the physical role of chlorophyll f is best supported as a low-energy radiative trap, the physical location should be close to or potentially within the charge-separating pigments to allow efficient transfer for charge separation on the 150 ps timescale. Target models can be developed that include a branching in the formation of the charge separation for either WL-PSI or FRL-PSI.
Collapse
Affiliation(s)
- Marius Kaucikas
- Department of Life Sciences, Imperial College London, London, United Kingdom
| | - Dennis Nürnberg
- Department of Life Sciences, Imperial College London, London, United Kingdom
| | - Gabriel Dorlhiac
- Department of Life Sciences, Imperial College London, London, United Kingdom
| | | | - Jasper J. van Thor
- Department of Life Sciences, Imperial College London, London, United Kingdom,Corresponding author
| |
Collapse
|
13
|
Herascu N, Hunter MS, Shafiei G, Najafi M, Johnson TW, Fromme P, Zazubovich V. Spectral Hole Burning in Cyanobacterial Photosystem I with P700 in Oxidized and Neutral States. J Phys Chem B 2016; 120:10483-10495. [PMID: 27661089 DOI: 10.1021/acs.jpcb.6b07803] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Nicoleta Herascu
- Department
of Physics, Concordia University, 7141 Sherbrooke Street West, Montreal, H4B 1R4, Quebec, Canada
| | - Mark S. Hunter
- Department
of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona, United States
| | - Golia Shafiei
- Department
of Physics, Concordia University, 7141 Sherbrooke Street West, Montreal, H4B 1R4, Quebec, Canada
| | - Mehdi Najafi
- Department
of Physics, Concordia University, 7141 Sherbrooke Street West, Montreal, H4B 1R4, Quebec, Canada
| | - T. Wade Johnson
- Department
of Chemistry, Susquehanna University, Selinsgrove, Pennsylvania, United States
| | - Petra Fromme
- Department
of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona, United States
| | - Valter Zazubovich
- Department
of Physics, Concordia University, 7141 Sherbrooke Street West, Montreal, H4B 1R4, Quebec, Canada
| |
Collapse
|
14
|
Chauvet AAP, Agarwal R, Haddad AA, van Mourik F, Cramer WA. Photo-induced oxidation of the uniquely liganded heme f in the cytochrome b6f complex of oxygenic photosynthesis. Phys Chem Chem Phys 2016; 18:12983-91. [PMID: 27108913 PMCID: PMC4990003 DOI: 10.1039/c6cp01592a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The ultrafast behavior of the ferrous heme f from the cytochrome b6f complex of oxygenic photosynthesis is revealed by means of transient absorption spectroscopy. Benefiting from the use of microfluidic technologies for handling the sample as well as from a complementary frame-by-frame analysis of the heme dynamics, the different relaxation mechanisms from vibrationally excited states are disentangled and monitored via the shifts of the heme α-absorption band. Under 520 nm laser excitation, about 85% of the heme f undergoes pulse-limited photo-oxidation (<100 fs), with the electron acceptor being most probably one of the adjacent aromatic amino acid residues. After charge recombination in 5.3 ps, the residual excess energy is dissipated in 3.6 ps. In a parallel pathway, the remaining 15% of the hemes directly relax from their excited state in 2.5 ps. In contrast to a vast variety of heme-proteins, including the homologous heme c1 from the cytochrome bc1 complex, there is no evidence that heme f photo-dissociates from its axial ligands. Due to its unique binding, with histidine and an unusual tyrosine as axial ligands, the heme f exemplifies a dependence of ultrafast dynamics on the structural environment.
Collapse
Affiliation(s)
- Adrien A P Chauvet
- Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratoire de Spectroscopie Ultrarapide (LSU), ISIC, Faculté des Sciences de Base and Lausanne Centre for Ultrafast Science (LACUS), Station 6, 1015 Lausanne, Switzerland.
| | | | | | | | | |
Collapse
|
15
|
Directionality of electron transfer in cyanobacterial photosystem I at 298 and 77 K. FEBS Lett 2015; 589:1412-7. [DOI: 10.1016/j.febslet.2015.04.048] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Revised: 04/22/2015] [Accepted: 04/23/2015] [Indexed: 11/23/2022]
|
16
|
Hasan SS, Zakharov SD, Chauvet A, Stadnytskyi V, Savikhin S, Cramer WA. A map of dielectric heterogeneity in a membrane protein: the hetero-oligomeric cytochrome b6f complex. J Phys Chem B 2014; 118:6614-25. [PMID: 24867491 PMCID: PMC4067154 DOI: 10.1021/jp501165k] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
![]()
The
cytochrome b6f complex,
a member of the cytochrome bc family that
mediates energy transduction in photosynthetic and respiratory membranes,
is a hetero-oligomeric complex that utilizes two pairs of b-hemes in a symmetric dimer to accomplish trans-membrane
electron transfer, quinone oxidation–reduction, and generation
of a proton electrochemical potential. Analysis of electron storage
in this pathway, utilizing simultaneous measurement of heme reduction,
and of circular dichroism (CD) spectra, to assay heme–heme
interactions, implies a heterogeneous distribution of the dielectric
constants that mediate electrostatic interactions between the four
hemes in the complex. Crystallographic information was used to determine
the identity of the interacting hemes. The Soret band CD signal is
dominated by excitonic interaction between the intramonomer b-hemes, bn and bp, on the electrochemically negative and positive sides
of the complex. Kinetic data imply that the most probable pathway
for transfer of the two electrons needed for quinone oxidation–reduction
utilizes this intramonomer heme pair, contradicting the expectation
based on heme redox potentials and thermodynamics, that the two higher
potential hemes bn on different monomers
would be preferentially reduced. Energetically preferred intramonomer
electron storage of electrons on the intramonomer b-hemes is found to require heterogeneity of interheme dielectric
constants. Relative to the medium separating the two higher potential
hemes bn, a relatively large dielectric
constant must exist between the intramonomer b-hemes,
allowing a smaller electrostatic repulsion between the reduced hemes.
Heterogeneity of dielectric constants is an additional structure–function
parameter of membrane protein complexes.
Collapse
Affiliation(s)
- S Saif Hasan
- Department of Biological Sciences and ‡Department of Physics, Purdue University , West Lafayette, Indiana 47907, United States
| | | | | | | | | | | |
Collapse
|
17
|
Chauvet A, Sarrou J, Lin S, Romberger SP, Golbeck JH, Savikhin S, Redding KE. Temporal and spectral characterization of the photosynthetic reaction center from Heliobacterium modesticaldum. PHOTOSYNTHESIS RESEARCH 2013; 116:1-9. [PMID: 23812833 DOI: 10.1007/s11120-013-9871-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Accepted: 06/11/2013] [Indexed: 06/02/2023]
Abstract
A time-resolved spectroscopic study of the isolated photosynthetic reaction center (RC) from Heliobacterium modesticaldum reveals that thermal equilibration of light excitation among the antenna pigments followed by trapping of excitation and the formation of the charge-separated state P800 (+)A0 (-) occurs within ~25 ps. This time scale is similar to that reported for plant and cyanobacterial photosystem I (PS I) complexes. Subsequent electron transfer from the primary electron acceptor A0 occurs with a lifetime of ~600 ps, suggesting that the RC of H. modesticaldum is functionally similar to that of Heliobacillus mobilis and Heliobacterium chlorum. The (A0 (-) - A0) and (P800 (+) - P800) absorption difference spectra imply that an 8(1)-OH-Chl a F molecule serves as the primary electron acceptor and occupies the position analogous to ec3 (A0) in PS I, while a monomeric BChl g pigment occupies the position analogous to ec2 (accessory Chl). The presence of an intense photobleaching band at 790 nm in the (A0 (-) - A0) spectrum suggests that the excitonic coupling between the monomeric accessory BChl g and the 8(1)-OH-Chl a F in the heliobacterial RC is significantly stronger than the excitonic coupling between the equivalent pigments in PS I.
Collapse
Affiliation(s)
- Adrien Chauvet
- Department of Physics, Purdue University, 525 Northwestern Ave, West Lafayette, IN 47907, USA
| | | | | | | | | | | | | |
Collapse
|
18
|
Semenov AY, Shelaev IV, Gostev FE, Mamedov MD, Shuvalov VA, Sarkisov OM, Nadtochenko VA. Primary steps of electron and energy transfer in photosystem I: Effect of excitation pulse wavelength. BIOCHEMISTRY (MOSCOW) 2012; 77:1011-20. [DOI: 10.1134/s0006297912090088] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
19
|
Chauvet A, Dashdorj N, Golbeck JH, Johnson TW, Savikhin S. Spectral resolution of the primary electron acceptor A0 in Photosystem I. J Phys Chem B 2012; 116:3380-6. [PMID: 22332796 DOI: 10.1021/jp211246a] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The reduced state of the primary electron acceptor of Photosystem I, A(0), was resolved spectroscopically in its lowest energy Q(y) region for the first time without the addition of chemical reducing agents and without extensive data manipulation. To carry this out, we used the menB mutant of Synechocystis sp. PCC 6803 in which phylloquinone is replaced by plastoquinone-9 in the A(1) sites of Photosystem I. The presence of plastoquinone-9 slows electron transfer from A(0) to A(1), leading to a long-lived A(0)(-) state. This allows its spectral signature to be readily detected in a time-resolved optical pump-probe experiment. The maximum bleaching (A(0)(-) - A(0)) was found to occur at 684 nm with a corresponding extinction coefficient of 43 mM(-1) cm(-1). The data show evidence for an electrochromic shift of an accessory chlorophyll pigment, suggesting that the latter Q(y) absorption band is centered around 682 nm.
Collapse
Affiliation(s)
- Adrien Chauvet
- Department of Physics, Purdue University, 525 Northwestern Ave, West Lafayette, Indiana 47907, USA
| | | | | | | | | |
Collapse
|
20
|
Renger T, Schlodder E. Optical properties, excitation energy and primary charge transfer in photosystem II: theory meets experiment. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2011; 104:126-41. [PMID: 21531572 DOI: 10.1016/j.jphotobiol.2011.03.016] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2010] [Revised: 03/04/2011] [Accepted: 03/21/2011] [Indexed: 11/29/2022]
Abstract
In this review we discuss structure-function relationships of the core complex of photosystem II, as uncovered from analysis of optical spectra of the complex and its subunits. Based on descriptions of optical difference spectra including site directed mutagenesis we propose a revision of the multimer model of the symmetrically arranged reaction center pigments, described by an asymmetric exciton Hamiltonian. Evidence is provided for the location of the triplet state, the identity of the primary electron donor, the localization of the cation and the secondary electron transfer pathway in the reaction center. We also discuss the stationary and time-dependent optical properties of the CP43 and CP47 subunits and the excitation energy transfer and trapping-by-charge-transfer kinetics in the core complex.
Collapse
Affiliation(s)
- Thomas Renger
- Institut für Theoretische Physik, Johannes Kepler Universität, Abteilung Theoretische Biophysik, Austria.
| | | |
Collapse
|
21
|
Abramavicius D, Mukamel S. Exciton delocalization and transport in photosystem I of cyanobacteria Synechococcus elongates: simulation study of coherent two-dimensional optical signals. J Phys Chem B 2009; 113:6097-108. [PMID: 19351124 PMCID: PMC2905166 DOI: 10.1021/jp811339p] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Electronic excitations and the optical properties of the photosynthetic complex PSI are analyzed using an effective exciton model developed by Vaitekonis et al. [Photosynth. Res. 2005, 86, 185]. States of the reaction center, the linker states, the highly delocalized antenna states and the red states are identified and assigned in absorption and circular dichroism spectra by taking into account the spectral distribution of density of exciton states, exciton delocalization length, and participation ratio in the reaction center. Signatures of exciton cooperative dynamics in nonchiral and chirality-induced two-dimensional (2D) photon-echo signals are identified. Nonchiral signals show resonances associated with the red, the reaction center, and the bulk antenna states as well as transport between them. Spectrally overlapping contributions of the linker and the delocalized antenna states are clearly resolved in the chirality-induced signals. Strong correlations are observed between the delocalized antenna states, the linker states, and the RC states. The active space of the complex covering the RC, the linker, and the delocalized antenna states is common to PSI complexes in bacteria and plants.
Collapse
Affiliation(s)
- Darius Abramavicius
- Chemistry Department, University of California Irvine, California 92697-2025, USA.
| | | |
Collapse
|
22
|
Simonson T. Dielectric relaxation in proteins: the computational perspective. PHOTOSYNTHESIS RESEARCH 2008; 97:21-32. [PMID: 18443919 DOI: 10.1007/s11120-008-9293-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2007] [Accepted: 02/18/2008] [Indexed: 05/26/2023]
Abstract
In photoexcitation and electron transfer, a new dipole or charge is introduced, and the structure is adjusted. This adjustment represents dielectric relaxation, which is the focus of this review. We concentrate on a few selected topics. We discuss linear response theory, as a unifying framework and a tool to describe non-equilibrium states. We review recent, molecular dynamics simulation studies that illustrate the calculation of dynamic and thermodynamic properties, such as Stokes shifts or reorganization free energies. We then turn to the macroscopic, continuum electrostatic view. We recall the physical definition of a dielectric constant and revisit the decomposition of the free energy into a reorganization and a static term. We review some illustrative continuum studies and discuss some difficulties that can arise with the continuum approach. In conclusion, we consider recent developments that will increase the accuracy and broaden the scope of all these methods.
Collapse
Affiliation(s)
- Thomas Simonson
- Laboratoire de Biochimie (UMR CNRS 7654), Department of Biology, Ecole Polytechnique, 91128 Palaiseau, France.
| |
Collapse
|
23
|
Spectroscopic properties of reaction center pigments in photosystem II core complexes: revision of the multimer model. Biophys J 2008; 95:105-19. [PMID: 18339736 DOI: 10.1529/biophysj.107.123935] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Absorbance difference spectra associated with the light-induced formation of functional states in photosystem II core complexes from Thermosynechococcus elongatus and Synechocystis sp. PCC 6803 (e.g., P(+)Pheo(-),P(+)Q(A)(-),(3)P) are described quantitatively in the framework of exciton theory. In addition, effects are analyzed of site-directed mutations of D1-His(198), the axial ligand of the special-pair chlorophyll P(D1), and D1-Thr(179), an amino-acid residue nearest to the accessory chlorophyll Chl(D1), on the spectral properties of the reaction center pigments. Using pigment transition energies (site energies) determined previously from independent experiments on D1-D2-cytb559 complexes, good agreement between calculated and experimental spectra is obtained. The only difference in site energies of the reaction center pigments in D1-D2-cytb559 and photosystem II core complexes concerns Chl(D1). Compared to isolated reaction centers, the site energy of Chl(D1) is red-shifted by 4 nm and less inhomogeneously distributed in core complexes. The site energies cause primary electron transfer at cryogenic temperatures to be initiated by an excited state that is strongly localized on Chl(D1) rather than from a delocalized state as assumed in the previously described multimer model. This result is consistent with earlier experimental data on special-pair mutants and with our previous calculations on D1-D2-cytb559 complexes. The calculations show that at 5 K the lowest excited state of the reaction center is lower by approximately 10 nm than the low-energy exciton state of the two special-pair chlorophylls P(D1) and P(D2) which form an excitonic dimer. The experimental temperature dependence of the wild-type difference spectra can only be understood in this model if temperature-dependent site energies are assumed for Chl(D1) and P(D1), reducing the above energy gap from 10 to 6 nm upon increasing the temperature from 5 to 300 K. At physiological temperature, there are considerable contributions from all pigments to the equilibrated excited state P*. The contribution of Chl(D1) is twice that of P(D1) at ambient temperature, making it likely that the primary charge separation will be initiated by Chl(D1) under these conditions. The calculations of absorbance difference spectra provide independent evidence that after primary electron transfer the hole stabilizes at P(D1), and that the physiologically dangerous charge recombination triplets, which may form under light stress, equilibrate between Chl(D1) and P(D1).
Collapse
|
24
|
Hastings G, Wang R. Vibrational mode frequency calculations of chlorophyll-d for assessing (P740(+)-P740) FTIR difference spectra obtained using photosystem I particles from Acaryochloris marina. PHOTOSYNTHESIS RESEARCH 2008; 95:55-62. [PMID: 17710563 DOI: 10.1007/s11120-007-9228-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2007] [Accepted: 07/16/2007] [Indexed: 05/16/2023]
Abstract
Acaryochloris marina is an oxygen-evolving organism that utilizes chlorophyll-d for light induced photochemistry. In photosystem I particles from Acaryochloris marina, the primary electron donor is called P740, and it is thought that P740 consist of two chlorophyll-d molecules. (P740(+)-P740) FTIR difference spectra have been produced, and vibrational features that are specific to chlorophyll-d (and not chlorophyll-a) were observed, supporting the idea that P740 consists chlorophyll-d molecules. Although bands in the (P740(+)-P740) FTIR difference spectra were assigned specifically to chlorophyll-d, how these bands shifted, and how their intensities changed, upon cation formation was never considered. Without this information it is difficult to draw unambiguous conclusions from the FTIR difference spectra. To gain a more detailed understanding of cation induced shifting of bands associated with vibrational modes of P740 we have used density functional theory to calculate the vibrational properties of a chlorophyll-d model in the neutral, cation and anion states. These calculations are shown to be of considerable use in interpreting bands in (P740(+)-P740) FTIR difference spectra. Our calculations predict that the 3(1) formyl C-H mode of chlorophyll-d upshifts/downshifts upon cation/anion formation, respectively. The mode intensity also decreases/increases upon cation/anion formation, respectively. The cation induced bandshift of the 3(1) formyl C-H mode of chlorophyll-d is also strongly dependant on the dielectric environment of the chlorophyll-d molecules. With this new knowledge we reassess the interpretation of bands that were assigned to 3(1) formyl C-H modes of chlorophyll-d in (P740(+)-P740) FTIR difference spectra. Considering our calculations in combination with (P740(+)-P740) FTIR DS we find that the most likely conclusions are that P740 is a dimeric Chl-d species, in an environment of low effective dielectric constant ( approximately 2-8). In the P740(+) state, charge is asymmetrically distributed over the two Chl-d pigments in a roughly 60:40 ratio.
Collapse
Affiliation(s)
- Gary Hastings
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, 30303, USA.
| | | |
Collapse
|
25
|
Schlodder E, Shubin VV, El-Mohsnawy E, Roegner M, Karapetyan NV. Steady-state and transient polarized absorption spectroscopy of photosytem I complexes from the cyanobacteria Arthrospira platensis and Thermosynechococcus elongatus. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2007; 1767:732-41. [PMID: 17321489 DOI: 10.1016/j.bbabio.2007.01.013] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2006] [Revised: 01/05/2007] [Accepted: 01/22/2007] [Indexed: 11/29/2022]
Abstract
Core antenna and reaction centre of photosystem I (PS I) complexes from the cyanobacteria Arthrospira platensis and Thermosynechococcus elongatus have been characterized by steady-state polarized absorption spectroscopy, including linear dichroism (LD) and circular dichroism (CD). CD spectra and the second derivatives of measured 77 K CD spectra reveal the spectral components found in the polarized absorption spectra indicating the excitonic origin of the spectral forms of chlorophyll in the PS I complexes. The CD bands at 669-670(+), 673(+), 680(-), 683-685(-), 696-697(-), and 711(-) nm are a common feature of used PSI complexes. The 77 K CD spectra of the trimeric PS I complexes exhibit also low amplitude components around 736 nm for A. platensis and 720 nm for T. elongatus attributed to red-most chlorophylls. The LD measurements indicate that the transition dipole moments of the red-most states are oriented parallel to the membrane plane. The formation of P700(+)A(1)(-) or (3)P700 was monitored by time-resolved difference absorbance and LD spectroscopy to elucidate the spectral properties of the PS I reaction centre. The difference spectra give strong evidence for the delocalization of the excited singlet states in the reaction centre. Therefore, P700 cannot be considered as a dimer but should be regarded as a multimer of the six nearly equally coupled reaction centre chlorophylls in accordance with structure-based calculations. On the basis of the results presented in this work and earlier work in the literature it is concluded that the triplet state is localized most likely on P(A), whereas the cation is localized most likely on P(B).
Collapse
Affiliation(s)
- Eberhard Schlodder
- Max-Volmer-Laboratorium für Biophysikalische Chemie, Technische Universität Berlin, Strasse des 17.Juni 135, 10623 Berlin, Germany.
| | | | | | | | | |
Collapse
|
26
|
|
27
|
Byrdin M, Santabarbara S, Gu F, Fairclough WV, Heathcote P, Redding K, Rappaport F. Assignment of a kinetic component to electron transfer between iron–sulfur clusters FX and FA/B of Photosystem I. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:1529-38. [PMID: 16945322 DOI: 10.1016/j.bbabio.2006.06.016] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2006] [Revised: 06/14/2006] [Accepted: 06/16/2006] [Indexed: 10/24/2022]
Abstract
We studied the kinetics of reoxidation of the phylloquinones in Chlamydomonas reinhardtii Photosystem I using site-directed mutations in the PhQ(A)-binding site and of the residues serving as the axial ligand to ec3(A) and ec3(B) chlorophylls. In wild type PS I, these kinetics are biphasic, and mutations in the binding region of PhQ(A) induced a specific slowing down of the slow component. This slowing allowed detection of a previously unobserved 180-ns phase having spectral characteristics that differ from electron transfer between phylloquinones and F(X). The new kinetic phase thus reflects a different reaction that we ascribe to oxidation of F(X)(-) by the F(A/B) FeS clusters. These absorption changes partly account for the differences between the spectra associated with the two kinetic components assigned to phylloquinone reoxidation. In the mutant in which the axial ligand to ec3(A) (PsaA-Met688) was targeted, about 25% of charge separations ended in P(700)(+)A(0)(-) charge recombination; no such recombination was detected in the B-side symmetric mutant. Despite significant changes in the amplitude of the components ascribed to phylloquinone reoxidation in the two mutants, the overall nanosecond absorption changes were similar to the wild type. This suggests that these absorption changes are similar for the two different phylloquinones and that part of the differences between the decay-associated spectra of the two components reflect a contribution from different electron acceptors, i.e. from an inter-FeS cluster electron transfer.
Collapse
Affiliation(s)
- Martin Byrdin
- Institut de Biologie Physico-Chimique, UMR 7141 CNRS/Paris 6, 13 Rue Pierre et Marie Curie, 75005 Paris, France
| | | | | | | | | | | | | |
Collapse
|
28
|
Riley KJ, Zazubovich V, Jankowiak R. Frequency-Domain Spectroscopic Study of the PS I−CP43‘ Supercomplex from the Cyanobacterium Synechocystis PCC 6803 Grown under Iron Stress Conditions. J Phys Chem B 2006; 110:22436-46. [PMID: 17091985 DOI: 10.1021/jp063691f] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Absorption, fluorescence excitation, emission, and hole-burning (HB) spectra were measured at liquid helium temperatures for the PS I-CP43' supercomplexes of Synechocystis PCC 6803 grown under iron stress conditions and for respective trimeric PS I cores. Results are compared with those of room temperature, time-domain experiments (Biochemistry 2003, 42, 3893) as well as with the low-temperature steady-state experiments on PS I-CP43' supercomplexes of Synechococcus PCC 7942 (Biochim. Biophys. Acta 2002, 1556, 265). In contrast to the CP43' of Synechococcus PCC 7942, CP43' of Synechocystis PCC 6803 possesses two low-energy states analogous to the quasidegenerate states A and B of CP43 of photosystem II (J. Phys. Chem. B 2000, 104, 11805). Energy transfer between the CP43' and the PS I core occurs, to a significant degree, through the state A, characterized with a broader site distribution function (SDF). It is demonstrated that the low temperature (T = 5 K) excitation energy transfer (EET) time between the state A of CP43' (IsiA) and the PS I core in PS I-CP43' supercomplexes from Synechocystis PCC 6803 is about 60 ps, which is significantly slower than the EET observed at room temperature. Our results are consistent with fast (< or =10 ps) energy transfer from state B to state A in CP43'. Energy absorbed by the CP43' manifold has, on average, a greater chance of being transferred to the reaction center (RC) and utilized for charge separation than energy absorbed by the PS I core antenna. This indicates that energy is likely transferred from the CP43' to the RC along a well-defined path and that the "red antenna states" of the PS I core are localized far away from that path, most likely on the B7-A32 and B37-B38 dimers in the vicinity of the PS I trimerization domain (near PsaL subunit). We argue that the A38-A39 dimer does not contribute to the red antenna region.
Collapse
Affiliation(s)
- Kerry J Riley
- Ames Laboratory-USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011-3111, USA
| | | | | |
Collapse
|
29
|
Ren X, Yang Z, Kuang T. Solvent-induced changes in photochemical activity and conformation of photosystem I particles by glycerol. Biol Chem 2006; 387:23-9. [PMID: 16497161 DOI: 10.1515/bc.2006.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
It has been shown that a large number of water molecules coordinate with the pigments and subunits of photosystem I (PSI); however, the function of these water molecules remains to be clarified. In this study, the photosynthetic properties of PSI from spinach were investigated using different spectroscopic and activity measurements under conditions of decreasing water content caused by increasing concentrations of glycerol. The results show that glycerol addition caused pronounced changes in the photochemical activity of PSI particles. At low concentrations (<60%, v/v), glycerol stimulated the rate of oxygen uptake in PSI particles, while higher concentrations of glycerol cause inhibition of PSI activity. The capacity of P700 photooxidation also increased with glycerol concentrations lower than 60%. In contrast, this capacity decreased at higher glycerol concentrations. On the other hand, glycerol addition considerably affected the distribution of the bulk and red antenna chlorophyll (Chl) forms or states, with the population of red-shifted Chl forms augmented with increasing glycerol. In addition, glycerol-treated PSI particles showed a blue shift of the tryptophan fluorescence emission maximum and an increase in their capacity to bind the hydrophobic probe 1-anilino-8-naphthalene sulfonate, indicating a more non-polar environment for tryptophan residues and increased exposure of hydrophobic surfaces.
Collapse
Affiliation(s)
- Xiaohua Ren
- Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
| | | | | |
Collapse
|
30
|
Holzwarth AR, Müller MG, Niklas J, Lubitz W. Ultrafast transient absorption studies on photosystem I reaction centers from Chlamydomonas reinhardtii. 2: mutations near the P700 reaction center chlorophylls provide new insight into the nature of the primary electron donor. Biophys J 2006; 90:552-65. [PMID: 16258055 PMCID: PMC1367060 DOI: 10.1529/biophysj.105.059824] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2005] [Accepted: 10/03/2005] [Indexed: 11/18/2022] Open
Abstract
The energy transfer and charge separation kinetics in several core Photosystem I particles of Chlamydomonas reinhardtii with point mutations around the PA and PB reaction center chlorophylls (Chls) have been studied using ultrafast transient absorption spectroscopy in the femtosecond to nanosecond time range to characterize the influence on the early electron transfer processes. The data have been analyzed in terms of kinetic compartment models. The adequate description of the transient absorption kinetics requires three different radical pairs in the time range up to approximately 100 ps. Also a charge recombination process from the first radical pair back to the excited state is present in all the mutants, as already shown previously for the wild-type (Müller, M. G., J. Niklas, W. Lubitz, and A. R. Holzwarth. 2003. Biophys. J. 85:3899-3922; and Holzwarth, A. R., M. G. Müller, J. Niklas, and W. Lubitz. 2005. J. Phys. Chem. B. 109:5903-59115). In all mutants, the primary charge separation occurs with the same effective rate constant within the error limits as in the wild-type (>>350 ns(-1)), which implies an intrinsic rate constant of charge separation of <1 ps(-1). The rate constant of the secondary electron transfer process is slowed down by a factor of approximately 2 in the mutant B-H656C, which lacks the ligand to the central metal of Chl PB. For the mutant A-T739V, which breaks the hydrogen bond to the keto carbonyl of Chl PA, only a slight slowing down of the secondary electron transfer is observed. Finally for mutant A-W679A, which has the Trp near the PA Chl replaced, either no pronounced effect or, at best, a slight increase on the secondary electron transfer rate constants is observed. The effective charge recombination rate constant is modified in all mutants to some extent, with the strongest effect observed in mutant B-H656C. Our data strongly suggest that the Chls of the PA and PB pair, constituting what is traditionally called the "primary electron donor P700", are not oxidized in the first electron transfer process, but rather only in the secondary electron transfer step. We thus propose a new electron transfer mechanism for Photosystem I where the accessory Chl(s) function as the primary electron donor(s) and the A0 Chl(s) are the primary electron acceptor(s). This new mechanism also resolves in a straightforward manner the difficulty with the previous mechanism, where an electron would have to overcome a distance of approximately 14 A in <1 ps in a single step. If interpreted within a scheme of single-sided electron transfer, our data suggest that the B-branch is the active branch, although parallel A-branch activity cannot be excluded. All the mutations do affect to a varying extent the energy difference between the reaction center excited state RC* and the first radical pair and thus affect the rate constant of charge recombination. It is interesting to note that the new mechanism proposed is in fact analogous to the electron transfer mechanism in Photosystem II, where the accessory Chl also plays the role of the primary electron donor, rather than the special Chl pair P680 (Prokhorenko, V. and A. R. Holzwarth. 2000. J. Phys. Chem. B. 104:11563-11578).
Collapse
Affiliation(s)
- Alfred R Holzwarth
- Max-Planck-Institut für Bioanorganische Chemie, D-45470 Mülheim an der Ruhr, Germany.
| | | | | | | |
Collapse
|
31
|
Sacksteder CA, Bender SL, Barry BA. Role for bound water and CH-pi aromatic interactions in photosynthetic electron transfer. J Am Chem Soc 2005; 127:7879-90. [PMID: 15913378 DOI: 10.1021/ja050659a] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Photosystem I (PSI) is one of two photosynthetic reaction centers present in plants, algae, and cyanobacteria and catalyzes the reduction of ferredoxin and the oxidation of cytochrome c or plastocyanin. The PSI primary chlorophyll donor, which is oxidized in the primary electron-transfer events, is a heterodimer of chl a and a' called P700. It has been suggested that protein relaxation accompanies light-induced electron transfer in this reaction center (Dashdorj, N.; Xu, W.; Martinsson, P.; Chitnis, P. R.; Savikhin, S. Biophys. J. 2004, 86, 3121. Kim, S.; Sacksteder, C. A.; Bixby, K. A.; Barry, B. A. Biochemistry 2001, 40, 15384). To investigate the details of electron transfer and relaxation events in PSI, we have employed several experimental approaches. First, we report a pH-dependent viscosity effect on P700+ reduction; this result suggests a role for proton transfer in the PSI electron-transfer reactions. Second, we find that changes in hydration alter the rate of P700+ reduction and the interactions of P700 with the protein environment. This result suggests a role for bound water in electron transfer to P700+. Third, we present evidence that deuteration of the tyrosine aromatic side chain perturbs the vibrational spectrum, associated with P700+ reduction. We attribute this result to a linkage between CH-pi interactions and electron transfer to P700+.
Collapse
Affiliation(s)
- Colette A Sacksteder
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, St. Paul, Minnesota 55108, USA
| | | | | |
Collapse
|
32
|
Poluektov OG, Utschig LM, Dubinskij AA, Thurnauer MC. Electron transfer pathways and protein response to charge separation in photosynthetic reaction centers: time-resolved high-field ENDOR of the spin-correlated radical pair P865(+)QA(-). J Am Chem Soc 2005; 127:4049-59. [PMID: 15771542 DOI: 10.1021/ja043063g] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Recently we reported the first observation of time-resolved (TR) high-frequency (HF) electron nuclear double resonance (ENDOR) of the transient charge separated state P865(+)Q(-)A in purple photosynthetic bacterial reaction centers (RC) (Poluektov, O. G., et al. J. Am. Chem. Soc. 2004, 126, 1644-1645). The high resolution and orientational selectivity of HF ENDOR allows us to directly probe protein environments by spectrally selecting specific nuclei in isotopically labeled samples. A new phenomenon associated with the spin correlated radical pair (SCRP) nature of P865(+)Q(-)A was observed. The TR-HF ENDOR spectra of protein nuclei (protons) surrounding deuterated QA(-) exhibit a derivative-like, complicated line shape, which differs considerably from the HF ENDOR spectrum of the protein nuclei surrounding thermally equilibrated QA(-). Here, a theoretical analysis of these observations is presented that shows that the positions and amplitudes of ENDOR lines contain information on hyperfine interactions (HFI) of a particular nucleus (a proton of the protein) with both correlated electron spins. Thus, spin density delocalization in the protein environment between the SCRP donor and acceptor molecules can be revealed via HF ENDOR. Novel approaches for acquiring and analyzing SCRP ENDOR that simplify interpretation of the spectra are discussed. Furthermore, we report here that the positions of the ENDOR lines of the SCRP shift with an increase in the time after laser flash, which initiates electron transfer. These shifts provide direct spectroscopic evidence of reorganization of the protein environment to accommodate the donor-acceptor charge-separated state P865(+)QA(-).
Collapse
Affiliation(s)
- Oleg G Poluektov
- Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
| | | | | | | |
Collapse
|
33
|
Dahlbom MG, Reimers * JR. Successes and failures of time-dependent density functional theory for the low-lying excited states of chlorophylls. Mol Phys 2005. [DOI: 10.1080/00268970412331333528] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
|
34
|
Wenk SO, Schneider D, Boronowsky U, Jäger C, Klughammer C, de Weerd FL, van Roon H, Vermaas WFJ, Dekker JP, Rögner M. Functional implications of pigments bound to a cyanobacterial cytochrome b6f complex. FEBS J 2004; 272:582-92. [PMID: 15654895 DOI: 10.1111/j.1742-4658.2004.04501.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
A highly purified cytochrome b(6)f complex from the cyanobacterium Synechocystis sp. PCC 6803 selectively binds one chlorophyll a and one carotenoid in analogy to the recent published structure from two other b(6)f complexes. The unknown function of these pigments was elucidated by spectroscopy and site-directed mutagenesis. Low-temperature redox difference spectroscopy showed red shifts in the chlorophyll and carotenoid spectra upon reduction of cytochrome b(6), which indicates coupling of these pigments with the heme groups and thereby with the electron transport. This is supported by the correlated kinetics of these redox reactions and also by the distinct orientation of the chlorophyll molecule with respect to the heme cofactors as shown by linear dichroism spectroscopy. The specific role of the carotenoid echinenone for the cytochrome b(6)f complex of Synechocystis 6803 was elucidated by a mutant lacking the last step of echinenone biosynthesis. The isolated mutant complex preferentially contained a carotenoid with 0, 1 or 2 hydroxyl groups (most likely 9-cis isomers of beta-carotene, a monohydroxy carotenoid and zeaxanthin, respectively) instead. This indicates a substantial role of the carotenoid - possibly for strucure and assembly - and a specificity of its binding site which is different from those in most other oxygenic photosynthetic organisms. In summary, both pigments are probably involved in the structure, but may also contribute to the dynamics of the cytochrome b(6)f complex.
Collapse
Affiliation(s)
- Stephan-Olav Wenk
- Plant Biochemistry, Faculty for Biology, Ruhr-University Bochum, D-44780 Bochum, Germany
| | | | | | | | | | | | | | | | | | | |
Collapse
|