Multiple pathways for ultrafast transduction of light energy in the photosynthetic reaction center of
            <i>Rhodobacter sphaeroides</i>

Brederode, Marion E. van; Mourik, Frank van; Stokkum, Ivo H. M. van; Jones, Michael R.; Grondelle, Rienk van

doi:10.1073/pnas.96.5.2054

Cited by 110 publications

(119 citation statements)

References 36 publications

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“…S5 provides an example of comparable wavelength selected excitation of detergent solubilized RCs in solution. A more complete analysis has been carried out earlier by van Grondelle and coworkers demonstrating charge-separation that did not initiate from P* (15,16). Overall the transient absorption spectra and lifetimes measured in solution agree with those of single RC crystals, implying that the photochemical pathways are retained upon RC crystallization.…”

Section: Resultsmentioning

confidence: 72%

“…A component of primary charge separation occurring within the BChl A BPh A pair that does not evolve from P* was suggested previously based on decay associated spectral analysis of transients recoded from solutions at low temperature (15,16). However, the broadness of ultrafast pump pulses and overlap of the BChl A and BChl B absorptions prevents exclusive cofactor excitation.…”

Section: Discussionmentioning

confidence: 99%

“…Possible complexities in primary photochemistry for the bacterial RC multicofactor core have been suggested by findings of excitation energy-dependent variation photochemical pathways (13,14), including those that do not involve P* (15,16) that are analogous to the primary processes identified in Photosystem I and II reaction centers in oxygenic photosynthesis. (17)(18)(19)(20).…”

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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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Section: Resultsmentioning

confidence: 72%

Section: Discussionmentioning

confidence: 99%

mentioning

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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“…In line with the multimer model, in which the similarity in magnitude of the exciton coupling and energetic disorder results in exciton states delocalized over several cofactors (14,37), it is reasonable to consider that depending on protein conformation, distinct exciton states are present in the system. Each of these leads to a different pathway of charge separation, which has also been demonstrated for the bacterial reaction center (7)(8)(9). At this point a question arises: is the protein actively involved in the determination of a pathway or is this determination only dependent on random static disorder?…”

Section: Discussionmentioning

confidence: 99%

Two Different Charge Separation Pathways in Photosystem II

et al. 2010

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Charge separation is an essential step in the conversion of solar energy into chemical energy in photosynthesis. To investigate this process, we performed transient absorption experiments at 77 K with various excitation conditions on the isolated Photosystem II reaction center preparations from spinach. The results have been analyzed by global and target analysis and demonstrate that at least two different excited states, (Chl D1 Phe D1 )* and (P D1 P D2 Chl D1 )*, give rise to two different pathways for ultrafast charge separation. We propose that the disorder produced by slow protein motions causes energetic differentiation among reaction center complexes, leading to different charge separation pathways. Because of the low temperature, two excitation energy trap states are also present, generating charge-separated states on long time scales. We conclude that these slow trap states are the same as the excited states that lead to ultrafast charge separation, indicating that at 77 K charge separation can be either activation-less and fast or activated and slow.Charge separation is one of the key processes in photosynthetic energy conversion. After absorption of a photon by the photochemically active reaction center, an electronically excited state is transformed into a short-lived charge-separated state. Subsequent electron transfer results in a stable charge-separated state which ultimately powers the photosynthetic organism.Type II reaction centers found in purple bacteria and in oxygenevolving organisms (cyanobacteria, algae, and higher plants) are membrane proteins that contain four (bacterio)chlorophyll [(B)Chl] 1 and two (bacterio)pheophytin [(B)Phe] molecules arranged in two symmetric branches spanning the membrane in the center of the complex. It is established that only one branch is active in charge separation (1-4).The best understanding of the kinetics and energetics of charge separation has been obtained for the reaction center (RC) of photosynthetic purple bacteria (5). The central excitonically coupled special pair, P, of BChl molecules [P A and P B , ∼8 Å apart, center to center (6)], absorbing at ∼875 nm in Rhodobacter sphaeroides, are electronically excited after the energy transfer from the LH1 core antenna (absorbing at approximately equal energy). Then, an electron is transferred to the BChl molecule on the active branch (B A ) in 3 ps, and from B A to the BPhe (H A ) in 1 ps, resulting in the final charge-separated state, P þ H A -. However, in isolated reaction centers, excitation of the accessory BChl absorbing at ∼800 nm (B A ) resulted in an even faster charge separation, either via B A þ H A -or via P þ B A -(7-9). In vivo, this second route does not occur to a significant extent, because B A is too high in energy to receive excitation energy from the antenna.In the photosystem II reaction center (PSII RC) of oxygenevolving organisms, there is no special pair, and the similar distance of ∼10-11 Å between neighboring pigments in the center of the complex (10-13) gives rise to a...

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“…This results in a highly dominant path for charge separation, labelled the "L" side, whereas the non-dominant side is labelled "M". [20][21][22][23][24][25] Accordingly, there are altogether six pigment excitation energies to model with site energies E H L/M . The close proximity of the special pair BChls suggests strong interaction between their excited states, leading to strong, i.e., thermally robust, coherent sharing of excitation between the two BChls.…”

Section: Introductionmentioning

confidence: 99%

Excited state dynamics in photosynthetic reaction center and light harvesting complex 1

Strümpfer

Schulten

2012

The Journal of Chemical Physics

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Key to efficient harvesting of sunlight in photosynthesis is the first energy conversion process in which electronic excitation establishes a trans-membrane charge gradient. This conversion is accomplished by the photosynthetic reaction center (RC) that is, in case of the purple photosynthetic bacterium Rhodobacter sphaeroides studied here, surrounded by light harvesting complex 1 (LH1). The RC employs six pigment molecules to initiate the conversion: four bacteriochlorophylls and two bacteriopheophytins. The excited states of these pigments interact very strongly and are simultaneously influenced by the surrounding thermal protein environment. Likewise, LH1 employs 32 bacteriochlorophylls influenced in their excited state dynamics by strong interaction between the pigments and by interaction with the protein environment. Modeling the excited state dynamics in the RC as well as in LH1 requires theoretical methods, which account for both pigment-pigment interaction and pigment-environment interaction. In the present study we describe the excitation dynamics within a RC and excitation transfer between light harvesting complex 1 (LH1) and RC, employing the hierarchical equation of motion method. For this purpose a set of model parameters that reproduce RC as well as LH1 spectra and observed oscillatory excitation dynamics in the RC is suggested. We find that the environment has a significant effect on LH1-RC excitation transfer and that excitation transfers incoherently between LH1 and RC.

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Multiple pathways for ultrafast transduction of light energy in the photosynthetic reaction center of Rhodobacter sphaeroides

Cited by 110 publications

References 36 publications

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

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

Two Different Charge Separation Pathways in Photosystem II

Excited state dynamics in photosynthetic reaction center and light harvesting complex 1

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