Primary charge separation between P* and BA: Electron-transfer pathways in native and mutant GM203L bacterial reaction centers

Yakovlev, A. G.; Jones, Michael R.; Potter, Jonathan; Fyfe, Paul K.; Vasilieva, L. G.; Shkuropatov, A. Ya.; Shuvalov, Vladimir V

doi:10.1016/j.chemphys.2005.08.018

Cited by 38 publications

(35 citation statements)

References 55 publications

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“…In the experiments of Yakovlev et al, 30,31 an oscillation corresponding to a wavenumber of 130 cm -1 explains the initial part of the ∆A kinetics. As mentioned above, it is very likely, and in fact commonly accepted, that this is one of many possible dimer modes 23,24 that affects the orbital energy of the electron to be transferred from P. As described by Yakovlev et al 30 this initiates a wave packet motion toward an avoided crossing with the P + B A -state.…”

Section: Methods and Resultsmentioning

confidence: 96%

Trapped Water Molecule in the Charge Separation of a Bacterial Reaction Center

Ivashin

Larsson

2008

J. Phys. Chem. B

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Low-frequency oscillations in the absorption spectrum at 1020 nm, connected to the primary charge separation process in Rhodobacter sphaeroides, have been shown by Yakovlev et al. to be caused by rotational motion of an interstitial water molecule called "water-A". The same water molecule was shown by Potter et al. to increase the rate of charge separation by a factor of 8. We have carried out geometry optimization of water-A and its nearest atoms in the protein pocket, using density functional theory (DFT). There are strong hydrogen bonds to the axial imidazol group of the B part of the special pair (P=PAPB) and to the keto carbonyl group of ring V of the accessory chlorophyll (BA). Rotation of water-A is thus impossible in the electronic ground state. We have tried to support our speculations on other possible mechanisms by calculations. The P(+)BA(-) charge transfer state is stabilized by proton transfer from water-A and simultaneous proton transfer from the axial group of PB to water-A. After double proton transfer the hydrogen bond to the keto group disappears whereby a possibility opens up for almost free water rotation. The results therefore would explain the 32 cm(-1) oscillation of Yakovlev et al. The proposed mechanism assumes, however, that the general assumption that the activation energy disappears in the primary charge separation of bacterial photosynthesis, holds also for this special case.

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Section: Methods and Resultsmentioning

confidence: 96%

Trapped Water Molecule in the Charge Separation of a Bacterial Reaction Center

Ivashin

Larsson

2008

J. Phys. Chem. B

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“…Long-lived electronic coherence between the excited states of BPh and BChl was observed recently with 2-color photon echo experiments and was attributed to strong correlation between the protein-induced fluctuations in the transition energy levels of BChl and BPh (28). Electronic coherence between the cofactors allows the excitation to move coherently in space, enabling excited populations moving between different cofactors (24)(25)(26)(27)(28)(29). Based on the observation of electronic coherence is much longer lived at low temperature (28), the fact that we observe multicofactor transitions in the initial excited states only at cryogenic temperature suggests that electronic coherence might play an important role.…”

Section: Discussionmentioning

confidence: 99%

“…Analysis of a broad range of spectroscopic, excitation energy transfer, and electron transfer properties based on modeling the electronic structure of RCs have led to the concept that the hexameric cofactor core should be considered as a supermolecule with a ladder of exciton states composed of various contributions from each of the individual cofactors (21)(22)(23). Further, recent 2D electronic spectroscopic studies revealed surprisingly long-lived excited-state quantum coherence between cofactors preserved by correlated protein environments in photosynthetic light-harvesting and reaction center complexes (24)(25)(26)(27)(28)(29). This intercofactor electronic coherence is significant as a conduit for energy transfer that is potentially relevant to electron transfer as well.…”

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confidence: 99%

“…Interpigment electronic coupling has been studied by ultrafast pump-probe anisotropy spectroscopy in solution (28,30,31). Interpigment couplings in these measurements are detected through delocalized excited-state absorption changes, including coherent wave-packet motion, (25,(31)(32)(33) and by polarization studies that resolve transition moment anisotropies that deviate from the individual molecular reference frames (30,31,34,35). Limitations for photo-selection spectroscopy arise from the inability of excitation pulses to selectively isolate a single transition in regions of spectral congestion.…”

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confidence: 99%

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Cofactor-specific photochemical function resolved by ultrafast spectroscopy in photosynthetic reaction center crystals

Huang

Ponomarenko

Wiederrecht

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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High-resolution mapping of cofactor-specific photochemistry in photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides was achieved by polarization selective ultrafast spectroscopy in single crystals at cryogenic temperature. By exploiting the fixed orientation of cofactors within crystals, we isolated a single transition within the multicofactor manifold, and elucidated the sitespecific photochemical functions of the cofactors associated with the symmetry-related active A and inactive B branches. Transient spectra associated with the initial excited states were found to involve a set of cofactors that differ depending upon whether the monomeric bacteriochlorophylls, BChl A , BChl B , or the special pair bacteriochlorophyll dimer, P, was chosen for excitation. Proceeding from these initial excited states, characteristic photochemical functions were resolved. Specifically, our measurements provide direct evidence for an alternative charge separation pathway initiated by excitation of BChl A that does not involve P*. Conversely, the initial excited state produced by excitation of BChl B was found to decay by energy transfer to P. A clear sequential kinetic resolution of BChl A and the A-side bacteriopheophytin, BPh A , in the electron transfer proceeding from P* was achieved. These experiments demonstrate the opportunity to resolve photochemical function of individual cofactors within the multicofactor RC complexes using single crystal spectroscopy.photosynthesis | transient absorption | light-harvesting

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“…From the experimental side, a wealth of data on the rates and relative energies of the ET processes in PRCs are now available, thanks to the constant improvement in spectroscopical time-resolved techniques [7][8][9][10]. These advances have allowed for understanding many mechanistic details of the ET steps which ensure the high efficiency of energy conversion in photosynthetic centers.…”

Section: Introductionmentioning

confidence: 99%

Electron transfer rates and Franck–Condon factors: an application to the early electron transfer steps in photosynthetic reaction centers

2006

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Mechanistic aspects of some of the early electron transfer steps occurring in photosynthetic reaction centers are discussed. Starting from the normal modes of the redox cofactors involved in the electron transfer processes, we show how a series of quantities which regulate electron transfer rates, such as (i) the electron transfer active modes, (ii) the intramolecular reorganization energy, and (iii) the mutual couplings between the vibronic states of the donor and the acceptor, can be obtained and used to draw qualitative conclusions on ET rates.

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Primary charge separation between P* and BA: Electron-transfer pathways in native and mutant GM203L bacterial reaction centers

Cited by 38 publications

References 55 publications

Trapped Water Molecule in the Charge Separation of a Bacterial Reaction Center

Trapped Water Molecule in the Charge Separation of a Bacterial Reaction Center

Cofactor-specific photochemical function resolved by ultrafast spectroscopy in photosynthetic reaction center crystals

Electron transfer rates and Franck–Condon factors: an application to the early electron transfer steps in photosynthetic reaction centers

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