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Yakovlev AG, Taisova AS. Downhill excitation energy flow in reaction centers of purple bacteria Rhodospirillum rubrum G9. BIOCHIMICA ET BIOPHYSICA ACTA. BIOENERGETICS 2024; 1865:149499. [PMID: 39069149 DOI: 10.1016/j.bbabio.2024.149499] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2024] [Revised: 07/24/2024] [Accepted: 07/24/2024] [Indexed: 07/30/2024]
Abstract
Using femtosecond differential spectroscopy, excitation energy transfer in reaction centers (RCs) of the carotenoidless strain of purple bacteria Rhodospirillum rubrum G9 was studied at room temperature. Excitation and probing of the Qy, Qx and Soret absorption bands of the RCs were carried out by pulses with duration of 25-30 fs. Modeling of ΔA (light - dark) kinetics made it possible to estimate the characteristic time of various stages of excitation energy transformation. It is shown that the dynamics of the downhill energy flow in the RCs is determined both by the internal energy conversion Soret→ Qx → Qy in each cofactor and by the energy transfer H* → B* → P* (H - bacteriopheophytin, B - bacteriochlorophyll a, P - bacteriochlorophyll a dimer) between cofactors. The transfer of energy between the upper excited levels (Soret and Qx) of the cofactors accelerates its arrival to the lower exciton level of the P, from where charge separation begins. It turned out that all conversion and energy transfer processes occur within 40-160 fs: the conversion Soret → Qx occurs in 40-50 fs, the conversion Qx → Qy occurs in 100-140 fs, the transfer H* → B* has a time constant of 80-120 fs, and the transfer B* → P* has a time constant of 130-160 fs. The rate of energy transfer between the upper excited levels is close to the rate of transfer between Qy levels.
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Affiliation(s)
- Andrei G Yakovlev
- Lomonosov Moscow State University, Belozersky Institute of Physico-Chemical Biology, Leninskie Gory, 119991 Moscow, Russian Federation.
| | - Alexandra S Taisova
- Lomonosov Moscow State University, Belozersky Institute of Physico-Chemical Biology, Leninskie Gory, 119991 Moscow, Russian Federation
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Zarrabi N, Obondi CO, Lim GN, Seetharaman S, Boe BG, D'Souza F, Poddutoori PK. Charge-separation in panchromatic, vertically positioned bis(donor styryl)BODIPY-aluminum(iii) porphyrin-fullerene supramolecular triads. NANOSCALE 2018; 10:20723-20739. [PMID: 30398274 DOI: 10.1039/c8nr06649c] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Three, broad band capturing, vertically aligned supramolecular triads, R2-BDP-AlPorF3←Im-C60 [R = H, styryl (C2H2-Ph), C2H2-TPA (TPA = triphenylamine); ← = coordinate bond], have been constructed using BODIPY derivative (BDP, BDP-Ph2 or BDP-TPA2), 5,10,15,20-tetrakis(3,4,5-trifluorophenyl)aluminum(iii) porphyrin (AlPorF3) and fullerene (C60) entities. The C60 and BDP units are bound to the Al center on the opposite faces of the porphyrin: the BDP derivative through a covalent axial bond using a benzoate spacer and the C60 through a coordination bond via an appended imidazole. Owing to the bis-styryl functionality on BDP, the constructed dyads and triads exhibited panchromatic light capture. Due to the diverse absorption and redox properties of the selected entities, it was possible to demonstrate excitation wavelength dependent photochemical events. In the case of the BDP-AlPorF3 dyad, selective excitation of BDP resulted in singlet-singlet energy transfer to AlPorF3 (kEnT = 1.0 × 1010 s-1). On the other hand, excitation of the AlPorF3 entity in the BDP-AlPorF3←Im-C60 triad revealed charge separation leading to the BDP-(AlPorF3)˙+-(C60)˙- charge separated state (kCS = 2.43 × 109 s-1). In the case of the Ph2-BDP-AlPorF3 dyad, energy transfer from 1AlPorF3* to 1(Ph2-BDP)* was witnessed (kEnT = 1.0 × 1010 s-1); however, upon assembling the supramolecular triad, (Ph2-BDP)-AlPorF3←Im-C60, electron transfer from 1AlPorF3* to C60 (kCS = 3.35 × 109 s-1), followed by hole shift (kHS = 1.00 × 109 s-1) to Ph2-BDP, was witnessed. Finally, in the case of the TPA2-BDP-AlPorF3←Im-C60 triad, only electron transfer leading to the (TPA2-BDP)˙+-AlPorF3←Im-(C60)˙- charge separated state, and no energy transfer, was observed. The facile oxidation of Ph2-BDP and TPA2-BDP compared to AlPorF3 in the latter two triads facilitated charge separation through either an electron migration or hole transfer mechanism depending on the initial excitation. The charge-separated states in these triads persisted for about 20 ns.
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Affiliation(s)
- Niloofar Zarrabi
- Department of Chemistry & Biochemistry, University of Minnesota Duluth, 1039 University Drive, Duluth, Minnesota 55812, USA.
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Achary BS, Ramya AR, Nanubolu JB, Seetharaman S, Lim GN, Jang Y, D’Souza F, Giribabu L. Axially substituted phosphorous(v) corrole with polycyclic aromatic hydrocarbons: syntheses, X-ray structures, and photoinduced energy and electron transfer studies. NEW J CHEM 2018. [DOI: 10.1039/c7nj04363e] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Excited state energy and electron transfer processes in naphthalene and pyrene appended phosphorous(v) corroles.
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Affiliation(s)
- B. Shivaprasad Achary
- Inorganic & Physical Chemistry Division
- CSIR-Indian Institute of Chemical Technology
- Hyderabad-500007
- India
| | - A. R. Ramya
- Inorganic & Physical Chemistry Division
- CSIR-Indian Institute of Chemical Technology
- Hyderabad-500007
- India
| | - Jagadeesh Babu Nanubolu
- Laboratory of X-ray Crystallography
- CSIR-Indian Institute of Chemical Technology
- Hyderabad-500007
- India
| | | | - Gary N. Lim
- Department of Chemistry
- University of North Texas
- Denton
- USA
| | - Youngwoo Jang
- Department of Chemistry
- University of North Texas
- Denton
- USA
| | | | - Lingamallu Giribabu
- Inorganic & Physical Chemistry Division
- CSIR-Indian Institute of Chemical Technology
- Hyderabad-500007
- India
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Mamedov M, Nadtochenko V, Semenov A. Primary electron transfer processes in photosynthetic reaction centers from oxygenic organisms. PHOTOSYNTHESIS RESEARCH 2015; 125:51-63. [PMID: 25648636 DOI: 10.1007/s11120-015-0088-y] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Accepted: 01/12/2015] [Indexed: 05/22/2023]
Abstract
This minireview is written in honor of Vladimir A. Shuvalov, a pioneer in the area of primary photochemistry of both oxygenic and anoxygenic photosyntheses (See a News Report: Allakhverdiev et al. 2014). In the present paper, we describe the current state of the formation of the primary and secondary ion-radical pairs within photosystems (PS) II and I in oxygenic organisms. Spectral-kinetic studies of primary events in PS II and PS I, upon excitation by ~20 fs laser pulses, are now available and reviewed here; for PS II, excitation was centered at 710 nm, and for PS I, it was at 720 nm. In PS I, conditions were chosen to maximally increase the relative contribution of the direct excitation of the reaction center (RC) in order to separate the kinetics of the primary steps of charge separation in the RC from that of the excitation energy transfer in the antenna. Our results suggest that the sequence of the primary electron transfer reactions is P680 → ChlD1 → PheD1 → QA (PS II) and P700 → A 0A/A 0B → A 1A/A 1B (PS I). However, alternate routes of charge separation in PS II, under different excitation conditions, are not ruled out.
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Affiliation(s)
- Mahir Mamedov
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, 119991, Moscow, Russia,
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Poddutoori PK, Lim GN, Sandanayaka ASD, Karr PA, Ito O, D'Souza F, Pilkington M, van der Est A. Axially assembled photosynthetic reaction center mimics composed of tetrathiafulvalene, aluminum(III) porphyrin and fullerene entities. NANOSCALE 2015; 7:12151-12165. [PMID: 26126984 DOI: 10.1039/c5nr01675d] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The distance dependence of sequential electron transfer has been studied in six, vertical, linear supramolecular triads, (TTF-Ph(n)-py → AlPor-Ph(m)-C60, n = 0, 1 and m = 1, 2, 3), constructed using tetrathiafulvalene (TTF), aluminum(III) porphyrin (AlPor) and fullerene (C60) entities. The C60 and TTF units are bound to the Al center on opposite faces of the porphyrin; the C60 through a covalent axial bond using a benzoate spacer, and the TTF through a coordination bond via an appended pyridine. Time-resolved optical and EPR spectroscopic methods and computational studies are used to demonstrate that excitation of the porphyrin leads to step-wise, sequential electron transfer (ET) between TTF and C60, and to study the electron transfer rates and exchange coupling between the components of the triads as a function of the bridge lengths. Femtosecond transient absorption studies show that the rates of charge separation, k(CS) are in the range of 10(9)-10(11) s(-1), depending on the length of the bridges. The lifetimes of the charge-separated state TTF˙(+)-C₆₀˙⁻ obtained from transient absorbance experiments and the singlet lifetimes of the radical pairs obtained by time-resolved EPR are in good agreement with each other and range from 60-130 ns in the triads. The time-resolved EPR data also show that population of the triplet sublevels of the charge-separated state in the presence of a magnetic field leads to much longer lifetimes of >1 μs. The data show that a modest stabilization of the charge separation lifetime occurs in the triads. The attenuation factor β = 0.36 Å(-1) obtained from the exchange coupling values between TTF˙(+) and C₆₀˙⁻ is consistent with values reported in the literature for oligophenylene bridged TTF-C60 conjugates. The singlet charge recombination lifetime shows a much weaker dependence on the distance between the donor and acceptor, suggesting that a simple superexchange model is not sufficient to describe the back reaction.
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Affiliation(s)
- Prashanth K Poddutoori
- Department of Chemistry, Brock University, 500 Glenridge Ave., St. Catharines, Ontario, Canada L2S 3A1.
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Guo Z, Lin S, Woodbury NW. Utilizing the Dynamic Stark Shift as a Probe for Dielectric Relaxation in Photosynthetic Reaction Centers During Charge Separation. J Phys Chem B 2013; 117:11383-90. [DOI: 10.1021/jp4037843] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Zhi Guo
- The
Biodesign Institute at Arizona State University, ‡Department of Chemistry and Biochemistry, and §Department of
Physics, Arizona State University, Tempe, Arizona 85287-5201, United States
| | - Su Lin
- The
Biodesign Institute at Arizona State University, ‡Department of Chemistry and Biochemistry, and §Department of
Physics, Arizona State University, Tempe, Arizona 85287-5201, United States
| | - Neal W. Woodbury
- The
Biodesign Institute at Arizona State University, ‡Department of Chemistry and Biochemistry, and §Department of
Physics, Arizona State University, Tempe, Arizona 85287-5201, United States
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Guo Z, Woodbury NW, Pan J, Lin S. Protein dielectric environment modulates the electron-transfer pathway in photosynthetic reaction centers. Biophys J 2013. [PMID: 23199926 DOI: 10.1016/j.bpj.2012.09.027] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The replacement of tyrosine by aspartic acid at position M210 in the photosynthetic reaction center of Rhodobacter sphaeroides results in the generation of a fast charge recombination pathway that is not observed in the wild-type. Apparently, the initially formed charge-separated state (cation of the special pair, P, and anion of the A-side bacteriopheophytin, H(A)) can decay rapidly via recombination through the neighboring bacteriochlorophyll (B(A)) soon after formation. The charge-separated state then relaxes over tens of picoseconds and recombination slows to the hundreds-of-picoseconds or nanosecond timescale. This dielectric relaxation results in a time-dependent blue shift of B(A)(-) absorption, which can be monitored using transient absorbance measurements. Protein dynamics also appear to modulate the electron transfer between H(A) and the next electron carrier, Q(A) (a ubiquinone). The kinetics of this reaction are complex in the mutant, requiring two kinetic terms, and the spectra associated with the two terms are distinct; a red shift of the H(A) ground-state bleaching is observed between the shorter and longer H(A)-to-Q(A) electron-transfer phases. The kinetics appears to be pH-independent, suggesting a negligible contribution of static heterogeneity originating from protonation/deprotonation in the ground state. A dynamic model based on the energy levels of the two early charge-separated states, P(+)B(A)(-) and P(+)H(A)(-), has been developed in which the energetics of these states is modulated by fast protein dielectric relaxations and this in turn alters both the kinetic complexity of the reaction and the reaction pathway.
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Affiliation(s)
- Zhi Guo
- The Biodesign Institute at Arizona State University, Tempe, Arizona, USA
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Du J, Kobayashi T, Watanabe K, Tamiaki H. B-side Electron Transfer in Bacterial Photosynthetic Reaction Centers Revealed by a Few-Cycle Pulse Laser. EPJ WEB OF CONFERENCES 2013. [DOI: 10.1051/epjconf/20134108012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Jankowiak R, Reppert M, Zazubovich V, Pieper J, Reinot T. Site Selective and Single Complex Laser-Based Spectroscopies: A Window on Excited State Electronic Structure, Excitation Energy Transfer, and Electron–Phonon Coupling of Selected Photosynthetic Complexes. Chem Rev 2011; 111:4546-98. [DOI: 10.1021/cr100234j] [Citation(s) in RCA: 122] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ryszard Jankowiak
- Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
| | - Mike Reppert
- Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
| | - Valter Zazubovich
- Department of Physics, Concordia University, Montreal H4B1R6 Quebec, Canada
| | - Jörg Pieper
- Max-Volmer-Laboratories for Biophysical Chemistry, Technical University of Berlin, Germany
- Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia
| | - Tonu Reinot
- Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
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Pudlak M, Pincak R. Electronic pathway in reaction centers from Rhodobacter sphaeroides and Chloroflexus aurantiacus. J Biol Phys 2010; 36:273-89. [PMID: 21629589 DOI: 10.1007/s10867-009-9183-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2008] [Accepted: 12/09/2009] [Indexed: 12/13/2022] Open
Abstract
The reaction centers (RC) of Chloroflexus aurantiacus and Rhodobacter sphaeroidesH(M182)L mutant were investigated. Prediction for electron transfer (ET) at very low temperatures was also performed. To describe the kinetics of the C. aurantiacus RCs, the incoherent model of electron transfer was used. It was shown that the asymmetry in electronic coupling parameters must be included to explain the experiments. For the description of R. sphaeroidesH(M182)L mutant RCs, the coherent and incoherent models of electron transfer were used. These two models are discussed with regard to the observed electron transfer kinetics. It seems likely that the electron transfer asymmetry in R. sphaeroides RCs is caused mainly by the asymmetry in the free energy levels of L- and M-side cofactors. In the case of C. aurantiacus RCs, the unidirectionality of the charge separation can be caused mainly by the difference in the electronic coupling parameters in two branches.
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Gibasiewicz K, Pajzderska M, Karolczak J, Dobek A. Excitation and electron transfer in reaction centers from Rhodobacter sphaeroides probed and analyzed globally in the 1-nanosecond temporal window from 330 to 700 nm. Phys Chem Chem Phys 2009; 11:10484-93. [PMID: 19890535 DOI: 10.1039/b912431d] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Global analysis of a set of room temperature transient absorption spectra of Rhodobacter sphaeroides reaction centers, recorded in wide temporal and spectral ranges and triggered by femtosecond excitation of accessory bacteriochlorophylls at 800 nm, is presented. The data give a comprehensive review of all spectral dynamics features in the visible and near UV, from 330 to 700 nm, related to the primary events in the Rb. sphaeroides reaction center: excitation energy transfer from the accessory bacteriochlorophylls (B) to the primary donor (P), primary charge separation between the primary donor and primary acceptor (bacteriopheophytin, H), and electron transfer from the primary to the secondary electron acceptor (ubiquinone). In particular, engagement of the accessory bacteriochlorophyll in primary charge separation is shown as an intermediate electron acceptor, and the initial free energy gap of approximately 40 meV, between the states P(+)B(A)(-) and P(+)H(A)(-) is estimated. The size of this gap is shown to be constant for the whole 230 ps lifetime of the P(+)H(A)(-) state. The ultrafast spectral dynamics features recorded in the visible range are presented against a background of results from similar studies performed for the last two decades.
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Affiliation(s)
- K Gibasiewicz
- Department of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland.
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Williams JC, Allen JP. Directed Modification of Reaction Centers from Purple Bacteria. THE PURPLE PHOTOTROPHIC BACTERIA 2009. [DOI: 10.1007/978-1-4020-8815-5_18] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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Mechanism of Charge Separation in Purple Bacterial Reaction Centers. THE PURPLE PHOTOTROPHIC BACTERIA 2009. [DOI: 10.1007/978-1-4020-8815-5_19] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Allen JP, Cordova JM, Jolley CC, Murray TA, Schneider JW, Woodbury NW, Williams JC, Niklas J, Klihm G, Reus M, Lubitz W. EPR, ENDOR, and special TRIPLE measurements of P(*+) in wild type and modified reaction centers from Rb. sphaeroides. PHOTOSYNTHESIS RESEARCH 2009; 99:1-10. [PMID: 18819016 DOI: 10.1007/s11120-008-9346-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2008] [Accepted: 07/22/2008] [Indexed: 05/26/2023]
Abstract
The influence of the protein environment on the primary electron donor, P, a bacteriochlorophyll a dimer, of reaction centers from Rhodobacter sphaeroides, has been investigated using electron paramagnetic resonance and electron nuclear double resonance spectroscopy. These techniques were used to probe the effects on P that are due to alteration of three amino acid residues, His L168, Asn L170, and Asn M199. The introduction of Glu at L168, Asp at L170, or Asp at M199 changes the oxidation/reduction midpoint potential of P in a pH-dependent manner (Williams et al. (2001) Biochemistry 40, 15403-15407). For the double mutant His L168 to Glu and Asn at L170 to Asp, excitation results in electron transfer along the A-side branch of cofactors at pH 7.2, but at pH 9.5, a long-lived state involving B-side cofactors is produced (Haffa et al. (2004) J Phys Chem B 108, 4-7). Using electron paramagnetic resonance spectroscopy, the mutants with alterations of each of the three individual residues and a double mutant, with changes at L168 and L170, were found to have increased linewidths of 10.1-11.0 G compared to the linewidth of 9.6 G for wild type. The Special TRIPLE spectra were pH dependent, and at pH 8, the introduction of aspartate at L170 increased the spin density ratio, rho (L)/rho (M), to 6.1 while an aspartate at the symmetry related position, M199, decreased the ratio to 0.7 compared to the value of 2.1 for wild type. These results indicate that the energy of the two halves of P changes by about 100 meV due to the mutations and are consistent with the interpretation that electrostatic interactions involving these amino acid residues contribute to the switch in pathway of electron transfer.
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Affiliation(s)
- J P Allen
- Department of Chemistry and Biochemistry and Center for Bioenergy and Photosynthesis, Arizona State University, Tempe, AZ, 85287-1604, USA.
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High-Field/High-Frequency Electron Paramagnetic Resonance Involving Single- and Multiple-Transition Schemes. BIOPHYSICAL TECHNIQUES IN PHOTOSYNTHESIS 2008. [DOI: 10.1007/978-1-4020-8250-4_14] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Haffa ALM, Lin S, Lobrutto R, Williams JC, Taguchi AKW, Allen JP, Woodbury NW. Environmental control of primary photochemistry in a mutant bacterial reaction center. J Phys Chem B 2007; 109:19923-8. [PMID: 16853576 DOI: 10.1021/jp052007e] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The core structure of the photosynthetic reaction center is quasisymmetric with two potential pathways (called A and B) for transmembrane electron transfer. Both the pathway and products of light-induced charge separation depend on local electrostatic interactions and the nature of the excited states generated at early times in reaction centers isolated from Rhodobacter sphaeroides. Here transient absorbance measurements were recorded following specific excitation of the Q(y)() transitions of P (the special pair of bacteriochlorophylls), the monomer bacteriochlorophylls (B(A) and B(B)), or the bacteriopheophytins (H(A) and H(B)) as a function of both buffer pH and detergent in a reaction center mutant with the mutations L168 His to Glu and L170 Asn to Asp in the vicinity of P and B(B). At a low pH in any detergent, or at any pH in a nonionic detergent (Triton X-100), the photochemistry of this mutant is faster than, but similar to, wild type (i.e. electron transfer occurs along the A-side, 390 nm excitation is capable of producing short-lived B-side charge separation (B(B)(+)H(B)(-)) but no long-lived B(B)(+)H(B)(-) is observed). Certain buffering conditions result in the stabilization of the B-side charge separated state B(B)(+)H(B)(-), including high pH in the zwitterionic detergent LDAO, even following excitation with low energy photons (800 or 740 nm). The most striking result is that conditions giving rise to stable B-side charge separation result in a lack of A-side charge separation, even when P is directly excited. The mechanism that links B(B)(+)H(B)(-) stabilization to this change in the photochemistry of P in the mutant is not understood, but clearly these two processes are linked and highly sensitive to the local electrostatic environment produced by buffering conditions (pH and detergent).
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Affiliation(s)
- Arlene L M Haffa
- Department of Chemistry and Biochemistry, Center for the Study of Early Events in Photosynthesis, School of Life Sciences, Arizona State University, Tempe, Arizona 85287-1604, USA
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Watson AJ, Fyfe PK, Frolov D, Wakeham MC, Nabedryk E, van Grondelle R, Breton J, Jones MR. Replacement or exclusion of the B-branch bacteriopheophytin in the purple bacterial reaction centre: The HB cofactor is not required for assembly or core function of the Rhodobacter sphaeroides complex. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2005; 1710:34-46. [PMID: 16181607 DOI: 10.1016/j.bbabio.2005.08.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2005] [Revised: 08/15/2005] [Accepted: 08/16/2005] [Indexed: 11/16/2022]
Abstract
All of the membrane-embedded cofactors of the purple bacterial reaction centre have well-defined functional or structural roles, with the exception of the bacteriopheophytin (H(B)) located approximately half-way across the membrane on the so-called inactive- or B-branch of cofactors. Sequence alignments indicate that this bacteriochlorin cofactor is a conserved feature of purple bacterial reaction centres, and a pheophytin is also found at this position in the Photosystem-II reaction centre. Possible structural or functional consequences of replacing the H(B) bacteriopheophytin by bacteriochlorophyll were investigated in the Rhodobacter sphaeroides reaction centre through mutagenesis of residue Leu L185 to His (LL185H). Results from absorbance spectroscopy indicated that the LL185H mutant assembled with a bacteriochlorophyll at the H(B) position, but this did not affect the capacity of the reaction centre to support photosynthetic growth, or change the kinetics of charge separation along the A-branch of cofactors. It was also found that mutation of residue Ala M149 to Trp (AM149W) caused the reaction centre to assemble without an H(B) bacteriochlorin, demonstrating that this cofactor is not required for correct assembly of the reaction centre. The absence of a cofactor at this position did not affect the capacity of the reaction centre to support photosynthetic growth, or the kinetics of A-branch electron transfer. A combination of X-ray crystallography and FTIR difference spectroscopy confirmed that the H(B) cofactor was absent in the AM149W mutant, and that this had not produced any significant disturbance of the adjacent ubiquinol reductase (Q(B)) site. The data are discussed with respect to possible functional roles of the H(B) bacteriopheophytin, and we conclude that the reason(s) for conservation of a bacteriopheophytin cofactor at this position in purple bacterial reaction centres are likely to be different from those underlying conservation of a pheophytin at the analogous position in Photosystem-II.
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Affiliation(s)
- Ashley J Watson
- Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
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Wakeham MC, Jones MR. Rewiring photosynthesis: engineering wrong-way electron transfer in the purple bacterial reaction centre. Biochem Soc Trans 2005; 33:851-7. [PMID: 16042613 DOI: 10.1042/bst0330851] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The purple bacterial reaction centre uses light energy to separate charge across the cytoplasmic membrane, reducing ubiquinone and oxidizing a c-type cytochrome. The protein possesses a macroscopic structural two-fold symmetry but displays a strong functional asymmetry, with only one of two available membrane-spanning branches of cofactors (the so-called A-branch) being used to catalyse photochemical charge separation. The factors underlying this functional asymmetry have been the subject of study for many years but are still not fully understood. Site-directed mutagenesis has been partially successful in rerouting electron transfer along the normally inactive B-branch, allowing comparison of the kinetics of equivalent electron transfer reactions on the two branches. Both the primary and secondary electron transfer steps on the B-branch appear to be considerably slower than their A-branch counterparts. The effectiveness of different mutations in rerouting electron transfer along the B-branch of cofactors is discussed.
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Affiliation(s)
- M C Wakeham
- Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
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Möbius K, Savitsky A, Schnegg A, Plato M, Fuchs M. High-field EPR spectroscopy applied to biological systems: characterization of molecular switches for electron and ion transfer. Phys Chem Chem Phys 2005; 7:19-42. [DOI: 10.1039/b412180e] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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