Stark effect (electroabsorption) spectroscopy of photosynthetic reaction centers at 1.5K: Evidence that the special pair has a large excited-state polarizability

Middendorf, Thomas R.; Mazzola, Laura T; Lao, Kaiqin; Steffen, Martín; Boxer, Steven G.

doi:10.1016/0005-2728(93)90147-8

Cited by 86 publications

(151 citation statements)

References 31 publications

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“…The wild-type 2ω Stark spectrum line shape (Figure 7, left panel) is similar to the second derivative of the absorption spectrum. This agreement of the line shapes suggests that ∆µ is the dominant contributor to the Stark spectrum (35). In the L131LH mutant (upper middle panel), the second derivative of the absorption is also similar to the 2ω Stark spectrum, again suggesting that ∆µ dominates the Stark spectrum.…”

Section: Resultsmentioning

confidence: 59%

“…The Stark effect for the special pair in wild-type reaction centers is substantially larger than for BChl, and this has been attributed to a relatively large ∆µ associated with the mixing of intradimer CT states with the exciton state (23). A more detailed Liptay analysis at very low temperatures showed that there is also a significant firstderivative component to the Stark spectrum, and this was interpreted as indicating a large difference polarizability for the special pair (35).…”

Section: Discussionmentioning

confidence: 99%

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Excited-State Electronic Asymmetry of the Special Pair in Photosynthetic Reaction Center Mutants: Absorption and Stark Spectroscopy

1999

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The electronic absorption line shape and Stark spectrum of the lowest energy Q y transition of the special pair in bacterial reaction centers contain a wealth of information on mixing with charge transfer states and electronic asymmetry. Both vary greatly in mutants that perturb the chemical composition of the special pair, such as the heterodimer mutants, and in mutants that alter interactions between the special pair and the surrounding reaction center protein, such as those that add or remove hydrogen bonds. The conventional and higher-order Stark spectra of a series of mutants are presented with the aim of developing a systematic description of the electronic structure of the excited state of the special pair that initiates photosynthetic charge separation. The mutants L168HF, M197FH, L131LH and L131LH/M160LH/ M197FH are known to have different hydrogen-bonding patterns to the special pair; however, they exhibit Stark effects that are very similar to wild type. By contrast, the addition of a hydrogen bond to the M-side keto carbonyl group of the special pair in M160LH greatly affects both the absorption and Stark spectra. The heterodimer special pairs, L173HL and M202HL, exhibit much larger Stark effects than wild type, with the greatest effect in the M-side mutant. Double mutants that combine the M-side heterodimer and a hydrogen-bond addition to the L-side of the special pair decrease the magnitude of the Stark effect. These results suggest that the electronic asymmetry of the dimer can be perturbed either by the formation of a heterodimer or by adding or deleting a hydrogen bond to a keto carbonyl group. From the pattern observed, it is concluded that the charge transfer state P L + P M -has a larger influence on the excited state of the dimer in wild type than the P L -P M + charge transfer state. Furthermore, asymmetry can be varied continuously, from extreme cases in which the heterodimer and hydrogen-bond effects work together, to cases in which hydrogen bonding offsets the effects of the heterodimer, to cases in which the homodimer is perturbed by hydrogen bonds. This leads to a unified model for understanding the effects of perturbations on the electronic symmetry of the special pair, and this can be connected with perturbations on the properties of many other systems such as donor-acceptor-substituted polyenes.Photoexcitation of a strongly interacting pair of bacteriochlorophyll (BChl) 1 molecules called the special pair or P in bacterial photosynthetic reaction centers (RCs) initiates a series of light-driven charge separation reactions. The singlet excited state of P, 1 P, transfers an electron within a few picoseconds to H L , a bacteriopheophytin (BPhe) molecule that is the initial electron acceptor (1). As shown in the upper part of Figure 1, there are two similar sets of chromophores related by a local C 2 axis of symmetry that can serve as electron acceptors, yet only the chromophores on the L side (the right side as illustrated, sometimes denoted the A branch) participate in the i...

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Section: Resultsmentioning

confidence: 59%

Section: Discussionmentioning

confidence: 99%

Excited-State Electronic Asymmetry of the Special Pair in Photosynthetic Reaction Center Mutants: Absorption and Stark Spectroscopy

1999

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“…[24][25][26][27] The technique is sensitive to changes in electronic environment of the pigment molecules and the interactions between pigments. [24][25][26][27][28][29][30][31] Since hydrogen bonds affect the electronic environment, the breaking or formation of hydrogen bonds is expected to influence the Stark spectrum. An example of the strong influence that the protein environment may exert on the Stark parameters is found for the carotenoid sphaeroidene in Rb.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the Light-Harvesting Antennas of Photosynthetic Purple Bacteria by Stark Spectroscopy. 2. LH2 Complexes: Influence of the Protein Environment

et al. 1997

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We have performed low-temperature Stark spectroscopy on a variety of different LH2 complexes from four photosynthetic bacteria, with the aim of characterizing the electric field response of the B800 and B850 absorption properties as a function of the protein environment. The following LH2 complexes were investigated: B800-850 and B800-820 of Rhodopseudomonas (Rps) acidophila; B800-850, B800-840 (RTyr +13 fPhe), and B800-826 (RTyr +13 fPhe, RTyr +14 fLeu) of Rhodobacter (Rb.) sphaeroides; B800-850 and B800-830 (obtained at high LDAO) of Ectothiorhodospira sp.; and B800-850 of Rhodospirillum (Rsp.) molischianum. For all these cases the spectral blue shift of B850 has been assigned to the loss hydrogenbonding interaction with the acetyl carbonyl of bacteriochlorophyll a. |∆µ| values for the 850 nm bands as well as for the blue-shifted bands are all on the order of 3-4.5 D/f. The loss of hydrogen-bonding interactions has only small effects on |∆µ| in these complexes. The values of the difference polarizability, Tr(∆r), are large (600-1400 Å 3 /f 2 ). The results are discussed in terms of crystal-structure-based models for LH2, in which pigment-pigment and pigment-protein interactions are considered; strong pigment-pigment interactions were found to be especially important. The values of |∆µ| for the 800 nm band are small, 1.0-1.5 D/f for LH2 complexes from Rb. sphaeroides and Rps. acidophila. However, in Rsp. molischianum and Ectothiorhodospira sp. |∆µ| values are much larger, of the order of 3 D/f. The difference in the B800 band is assigned to the difference in orientation of the B800 pigments in Rsp. molischianum and Ectothiorhodospira sp., as compared to the Rps. acidophila and Rb. sphaeroides. Due to the difference in orientation, the interactions of the Bchl a with the surrounding protein and neighboring carotenoid pigments are also not identical.

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“…This gives rise to Chls with a charge transfer-like excited state that can absorb a photon of a lower energy than the monomeric pigment exited state, thereby giving rise to the far-red light absorption (32). Similarly coupled Chls also exist in reaction center pigment assembly of PS I, PS II, and the bacterial reaction center (33)(34)(35)(36)(37). They have been reasonably well studied in the PS II reaction center, but less is known about such states in PS I.…”

Section: Photosystem I (Ps I)mentioning

confidence: 99%

“…Again, useful analogies with the PS II reaction center and the reaction center from purple bacteria can be drawn. The special pair in the reaction center from purple bacteria exhibits strong coupling (500 -1000 cm Ϫ1 (59)), and mixed charge transfer states are responsible for the special pair absorption in the very far-red at 900 nm (37). In the case of the PS II reaction center, the analogous Chls are much more weakly coupled (85-150 cm Ϫ1 ).…”

Section: Simultaneous Detection Of Ps I and Ps Ii Photochemistrymentioning

confidence: 99%

Defining the Far-red Limit of Photosystem I

Mokvist

Mamedov

2014

Journal of Biological Chemistry

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Stark effect (electroabsorption) spectroscopy of photosynthetic reaction centers at 1.5K: Evidence that the special pair has a large excited-state polarizability

Cited by 86 publications

References 31 publications

Excited-State Electronic Asymmetry of the Special Pair in Photosynthetic Reaction Center Mutants: Absorption and Stark Spectroscopy

Excited-State Electronic Asymmetry of the Special Pair in Photosynthetic Reaction Center Mutants: Absorption and Stark Spectroscopy

Characterization of the Light-Harvesting Antennas of Photosynthetic Purple Bacteria by Stark Spectroscopy. 2. LH2 Complexes: Influence of the Protein Environment

Defining the Far-red Limit of Photosystem I

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