New experimental approach to the estimation of rate of electron transfer from the primary to secondary acceptors in the photosynthetic electron transport chain of purple bacteria

Chamorovsky, Sergey K.; Remennikov, S.M.; Kononenko, A.A.; Венедиктов, П.С.; Rubin, A. B.

doi:10.1016/0005-2728(76)90222-x

Cited by 41 publications

(17 citation statements)

References 18 publications

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“…The existence of different protein conformations with very different characteristics was shown by the inhibition of electron transfer from Q A −• to Q B in RCs frozen in the dark (4,5); this was in contrast to viable electron transfer in RCs frozen under illumination. Subsequently several studies to investigate these conformers (i.e.…”

Section: Conformational Gatementioning

confidence: 99%

“…sphaeroides is an example of a gated electron transfer process. The reaction rate was shown to depend upon protein conformation based on changes of electron transfer upon freezing to cryogenic temperatures (4,5), crosslinking of the protein subunits (6) and embedding the protein in a glassy matrix (7) or PVA film (8). Furthermore, quinone (Q A ) substitution studies showed that the observed rate of electron transfer was independent of the driving force indicating a conformational gating mechanism (9).…”

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confidence: 99%

“…The configurations of the protein before and after reduction were trapped by freezing RCs to cryogenic temperature as has been done previously (4,5). Since in the native RC Q B −• cannot be formed by electron transfer from Q A −• in samples frozen in the dark (5, 43), we developed a modified RC (Fig.…”

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Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

et al. 2006

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The reaction center (RC) from Rhodobacter sphaeroides captures light energy by electron transfer between quinones Q A and Q B , involving a conformational gating step. In this work, conformational states of D +• Q B −• were trapped (80K) and studied using EPR spectroscopy in mutant RCs that lack Q A in which Q B was reduced by the bacteriopheophytin along the B-branch. In mutant RCs frozen in the dark, a light induced EPR signal due to D +• Q B −• formed in 30% of the sample with low quantum yield (0.2%-20%) and decayed in 6 s. A small signal with similar characteristics was also observed in native RCs. In contrast, the EPR signal due to D + Q B − in mutant RCs illuminated while freezing formed in ~ 95% of the sample that did not decay (τ >10 7 s) at 80K. In all samples, the observed gvalues were the same (g=2.0026) indicating that all active Q B −• was located in a proximal conformation coupled with the non-heme Fe 2+ . We propose that before electron transfer at 80K, the majority (~70%) of Q B , structurally located in the distal site, cannot be stably reduced, while the minor ( can be considered to be the initial and final states along the reaction coordinate for conformationallygated electron transfer.

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Section: Conformational Gatementioning

confidence: 99%

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Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

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“…In early studies, large differences in transfer rates were observed between RCs frozen in the light or in the dark (14,15,18). For RCs frozen in the dark and illuminated at cryogenic temperatures, the reaction k AB…”

Section: Introductionmentioning

confidence: 99%

“…Second, the rate is independent of driving force (13), showing that electron transfer is not the rate limiting step, indicating a conformational gating mechanism. Third, large differences in the rate of electron transfer at cryogenic temperature were found depending upon whether RCs are frozen in the light or in the dark, indicating that a structural change between the neutral and charge separated states is important for electron transfer (14,15). In the present study we use ENDOR spectroscopy (Electron Nuclear Double Resonance) (see e.g.…”

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ENDOR Spectroscopy Reveals Light Induced Movement of the H-Bond from Ser-L223 upon Forming the Semiquinone (Q_B^-^•) in Reaction Centers fromRhodobacter sphaeroides

et al. 2007

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Proton ENDOR spectroscopy was used to monitor local conformational changes in bacterial reaction centers (RC) associated with the electron transfer reaction DQ B → D +• Q B −• using mutant RCs capable of photo-reducing Q B at cryogenic temperatures. The charge separated state D +• Q B −• was studied in mutant RCs formed by either (i) illuminating at low temperature (77K) a sample frozen in the dark (ground state protein conformation) or (ii) illuminating at room temperature prior to and during the freezing (charge separated state protein conformation). The charge recombination rates from the two states differed greatly (>10 6 fold) as shown previously, indicating a structural change (Paddock et al (2006) Biochemistry 45, 14032 -14042). ENDOR spectra of Q B −• from both samples (35 GHz, 77K) showed three nearly identical sets of hyperfine couplings due to exchangeable protons that were similar to those for Q B −• in native RCs indicating that in all RCs, Q B −• was located at the proximal position near the metal site. In contrast, one set of H-bond couplings was observed only in the sample frozen under illumination in which the protein can relax prior to freezing. This H-bond was assigned to an interaction between the Ser-L223 hydroxyl and Q B −• based on its absence in Ser L223 → Ala mutant RCs. The Ser-L223 hydroxyl H-bond was also observed in the native RCs frozen under illumination. Thus, part of the protein relaxation in response to light induced charge separation involves the formation of an H-bond between the OH group of Ser-L223 and the anionic semiquinone Q B −• . This proton movement serves to stabilize the charge separated state and facilitate proton transfer to reduced Q B . KeywordsB-branch; bacterial reaction center; quinone movement; bacterial photosynthesis; electron transfer; nanoswitch Conformational changes in protein structure associated with electron transfer reactions play an important role in stabilizing the resultant charge separated state and determining the rates of electron transfer (1-3). In photosynthetic bacteria, reaction centers (RCs) perform the initial photochemical reactions in photosynthesis (see e.g. 4,5) resulting in the light induced reduction of a bound quinone, Q B . The reduction of Q B clearly demonstrates the influence of conformational dynamics on electron transfer. The overall reaction is shown by the solid curves in Figure 1. The first step is the initial photochemistry, a rapid (τ = 10 -10 s) light induced electron transfer from a electron donor species D (a bacteriochlorophyll dimer) along the A-branch (one of two pseudo-symmetric pathways) through a series of acceptor molecules bacteriochlorphyll, B A , bacteriopheophytin, H A , to a tightly bound quinone, Q A ( Figure 1). This is followed by a *To whom correspondence should be addressed. Phone: (858) 534-2504, Fax: (858) , is coupled to protein dynamics as shown by several experimental observations (for a review see 9). First, the rate of reaction is dependent on protein structure as illustrated by the ef...

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Theory of chemical reactions in condensed media and its applications to biological processes

Christov

1979

Int J of Quantum Chemistry

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The general aspects of a theory of dense-phase reactions, based on an accurate quantummechanical formulation of the rate equation, are considered. Using an adiabatic one-frequency oscillator model, the theory is applied to several important biological processes at low temperatures: the photinduced oxidation of cytochrome C by bacteriochlorophyll, the electron transfer from primary to secondary acceptors in bacterial photosynthesis, and the ligand rebinding of carbon oxide and P-chain of hemoglobin. A very good agreement between theory and experiment is found making use of no more than one or two (or even without any) adjustable parameters.The reactions in solution (liquid or solid phase), in particular, the chargetransfer processes, undoubtedly present a great interest for chemistry, electrochemistry, and biology. The recent development of the theory of these reactions is mainly based on a semiclassical treatment using transition state theory [ 11 or on a quantum-mechanical treatment in the framework of perturbation theory [2]. This implies either a classical motion of nuclei or a weak electronic interaction between both reactants and products.A more general consideration, which avoids to a large extent all these limitations, is possible on the basis of a quantum collision theory of chemical reactions [3], which applies to both gas-[4] and dense-phase (especially chargetransfer) [5] reactions.The goal of this paper is to consider the general aspects of this theory concerning the reactions in dense media, in particular, biological processes including electron transfer from a donor to an acceptor center.The usual quantum-mechanical treatment of both gas-and dense-phase reactions is based on an adiabatic separation of the motions of nuclei and electrons, which results from the large difference of their masses (Born-Oppenheimer approximation). Therefore, for any given electronic state, the slow nuclear motion is governed by an effective potential that arises from the fast electronic motion. Thus, the potential-energy surface, used to describe the interactions between atoms and molecules in a definite electronic state, involves both the field of the electron cloud and the internuclear repulsion energy.A simple model for a description of reactions in dense phases is based on the assumption that the nuclei are making small harmonic vibrations in both the initial and final states of the system. Then, the potential-energy surface arises from the intersection of two many-dimensional paraboloids corresponding to separate reactants and products, both including the solvent molecules. The electronic

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New experimental approach to the estimation of rate of electron transfer from the primary to secondary acceptors in the photosynthetic electron transport chain of purple bacteria

Cited by 41 publications

References 18 publications

Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

ENDOR Spectroscopy Reveals Light Induced Movement of the H-Bond from Ser-L223 upon Forming the Semiquinone (Q_B^-^•) in Reaction Centers fromRhodobacter sphaeroides

Theory of chemical reactions in condensed media and its applications to biological processes

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New experimental approach to the estimation of rate of electron transfer from the primary to secondary acceptors in the photosynthetic electron transport chain of purple bacteria

Cited by 41 publications

References 18 publications

Trapped Conformational States of Semiquinone (D+•QB-•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

Trapped Conformational States of Semiquinone (D+•QB-•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

ENDOR Spectroscopy Reveals Light Induced Movement of the H-Bond from Ser-L223 upon Forming the Semiquinone (QB-•) in Reaction Centers fromRhodobacter sphaeroides

Theory of chemical reactions in condensed media and its applications to biological processes

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Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

ENDOR Spectroscopy Reveals Light Induced Movement of the H-Bond from Ser-L223 upon Forming the Semiquinone (Q_B^-^•) in Reaction Centers fromRhodobacter sphaeroides