A New Pathway for Transmembrane Electron Transfer in Photosynthetic Reaction Centers of <i>Rhodobacter sphaeroides</i> Not Involving the Excited Special Pair

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

doi:10.1021/bi9703756

Cited by 123 publications

(134 citation statements)

References 30 publications

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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: 96%

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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Section: Discussionmentioning

confidence: 96%

Two Different Charge Separation Pathways in Photosystem II

et al. 2010

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“…Global analysis was performed as described in ref. 18 with the addition that the wavelength dependence of time-zero caused by group velocity dispersion (GVD) was taken into account. To achieve this, the rise and decay of the optical Kerr signal in CS 2 measured over the different wavelength windows was analyzed with a third-order polynomial function to describe the variation of time zero of the IRF.…”

Section: Methodsmentioning

confidence: 99%

“…This finding implied that an ultrafast and efficient alternative pathway for charge separation driven by monomeric pigments must exist. For the YM210W and YM210L mutants, in which the rate of P*-driven charge separation is slowed down to hundreds of ps, the presence of this alternative pathway for primary charge separation could be clearly resolved in pump-probe experiments (17,18). The charge-separated states formed from B A * in 200 fs were interpreted as P ϩ B A Ϫ and B A ϩ H A Ϫ , which in turn evolved to P ϩ H A Ϫ in a few ps.…”

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

Brederode

Mourik

Stokkum

et al. 1999

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

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A pathway of electron transfer is described that operates in the wild-type reaction center (RC) of the photosynthetic bacterium Rhodobacter sphaeroides. The pathway does not involve the excited state of the special pair dimer of bacteriochlorophylls (P*), but instead is driven by the excited state of the monomeric bacteriochlorophyll (B A *) present in the active branch of pigments along which electron transfer occurs. Pump-probe experiments were performed at 77 K on membrane-bound RCs by using different excitation wavelengths, to investigate the formation of the charge separated state P ؉ H A ؊ . In experiments in which P or B A was selectively excited at 880 nm or 796 nm, respectively, the formation of P ؉ H A ؊ was associated with similar time constants of 1.5 ps and 1.7 ps. However, the spectral changes associated with the two time constants are very different. Global analysis of the transient spectra shows that a mixture of P ؉ B A ؊ and P* is formed in parallel from B A * on a subpicosecond time scale. In contrast, excitation of the inactive branch monomeric bacteriochlorophyll (B B ) and the high exciton component of P (P ؉ ) resulted in electron transfer only after relaxation to P*. The multiple pathways for primary electron transfer in the bacterial RC are discussed with regard to the mechanism of charge separation in the RC of photosystem II from higher plants.

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“…These observations have led a number of authors to suggest that primary charge separation might occur differently in PSII, potentially initiated by excitation of B A rather than P A /P B . A number of groups have shown in bacterial reaction centers that it is possible to observe, under certain conditions, the formation of radical pair states upon direct excitation of B A (69,128,130,142). Dekker & van Grondelle (24) and Rutherford and coworkers (98,99) have suggested that in PSII the lack of spectral differentiation and the orientation of 3 P, respectively, might be consistent with a contribution of B * A to primary radical formation.…”

Section: Pheomentioning

confidence: 99%

STRUCTURE, DYNAMICS, AND ENERGETICS OF THE PRIMARY PHOTOCHEMISTRY OF PHOTOSYSTEM II OF OXYGENIC PHOTOSYNTHESIS

Diner

Rappaport

2002

Annu. Rev. Plant Biol.

389

246

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▪ Abstract Recent progress in two-dimensional and three-dimensional electron and X-ray crystallography of Photosystem II (PSII) core complexes has led to major advances in the structural definition of this integral membrane protein complex. Despite the overall structural and kinetic similarity of the PSII reaction centers to their purple nonsulfur photosynthetic bacterial homologues, the different cofactors and subtle differences in their spatial arrangement result in significant differences in the energetics and mechanism of primary charge separation. In this review we discuss some of the recent spectroscopic, structural, and mutagenic work on the primary and secondary electron transfer reactions in PSII, stressing what is experimentally novel, what new insights have appeared, and where questions of interpretation remain.

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A New Pathway for Transmembrane Electron Transfer in Photosynthetic Reaction Centers of Rhodobacter sphaeroides Not Involving the Excited Special Pair

Cited by 123 publications

References 30 publications

Two Different Charge Separation Pathways in Photosystem II

Two Different Charge Separation Pathways in Photosystem II

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

STRUCTURE, DYNAMICS, AND ENERGETICS OF THE PRIMARY PHOTOCHEMISTRY OF PHOTOSYSTEM II OF OXYGENIC PHOTOSYNTHESIS

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