Dependence of singlet-energy transfer on the conjugation length of carotenoids reconstituted into the LH1 complex from Rhodospirillum rubrum G9

Akahane, Junji; Rondonuwu, Ferdy S.; Fiedor, Leszek; Watanabe, Yasutaka; Koyama, Yasushi

doi:10.1016/j.cplett.2004.06.021

Cited by 53 publications

(81 citation statements)

References 17 publications

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“…This nondecaying signal forms a narrow peak centered at 530 nm and is generated within the first picosecond after excitation. The same signal was observed in LH1 complexes of Rhodospirillum rubrum reconstituted with spheroidene, and it was identified as a T 1 -T n transition due to a spheroidene triplet state (18).…”

Section: Resultssupporting

confidence: 49%

“…This strong dependence is ascribed to unfavorable spectral overlap between the carotenoid S 1 state and Q y band of BChl-a (1). Essentially the same situation was found for either native LH1 complexes (17) or LH1 reconstituted with different carotenoids (18) or for genetically modified LH2 complexes (19).…”

mentioning

confidence: 71%

“…Multiple pathways involving S 2 and S 1 routes are common in LH2 and LH1 complexes of purple bacteria binding carotenoids with N < 11 (1,15,18). When carotenoids with a longer conjugated bond system such as lycopene (16,18,19) or spirilloxanthin (18,31) are bound to LH2 or LH1 complexes the S 1 route becomes inactive, but the S 2 pathway is functional in all purple bacterial antenna studied so far. It is worth noting that the S 2 route is significantly diminished in light-harvesting complexes of dinoflagellates or diatoms binding the carbonyl carotenoids peridinin or fucoxanthin.…”

Section: Resultsmentioning

confidence: 99%

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Photoprotection in a purple phototrophic bacterium mediated by oxygen-dependent alteration of carotenoid excited-state properties

Šlouf

Chábera

Olsen³

et al. 2012

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

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Carotenoids are known to offer protection against the potentially damaging combination of light and oxygen encountered by purple phototrophic bacteria, but the efficiency of such protection depends on the type of carotenoid. Rhodobacter sphaeroides synthesizes spheroidene as the main carotenoid under anaerobic conditions whereas, in the presence of oxygen, the enzyme spheroidene monooxygenase catalyses the incorporation of a keto group forming spheroidenone. We performed ultrafast transient absorption spectroscopy on membranes containing reaction center-light-harvesting 1-PufX (RC-LH1-PufX) complexes and showed that when oxygen is present the incorporation of the keto group into spheroidene, forming spheroidenone, reconfigures the energy transfer pathway in the LH1, but not the LH2, antenna. The spheroidene/spheroidenone transition acts as a molecular switch that is suggested to twist spheroidenone into an s-trans configuration increasing its conjugation length and lowering the energy of the lowest triplet state so it can act as an effective quencher of singlet oxygen. The other consequence of converting carotenoids in RC-LH1-PufX complexes is that S 2 ∕S 1 ∕triplet pathways for spheroidene is replaced with a new pathway for spheroidenone involving an activated intramolecular charge-transfer (ICT) state. This strategy for RC-LH1-PufX-spheroidenone complexes maintains the light-harvesting cross-section of the antenna by opening an active, ultrafast S 1 ∕ICT channel for energy transfer to LH1 Bchls while optimizing the triplet energy for singlet oxygen quenching. We propose that spheroidene/spheroidenone switching represents a simple and effective photoprotective mechanism of likely importance for phototrophic bacteria that encounter light and oxygen.charge-transfer state | photoprotection | purple bacteria | photosynthesis C arotenoids are natural pigments that absorb light in the 450-550 nm spectral region and transfer the energy to (bacterio) chlorophylls [(B)Chls] thereby acting as important energy donors in photosynthesis (1). In addition to extending the spectral range for absorption of solar energy, carotenoids play a structural role in light-harvesting (antenna) complexes (2, 3). Finally, carotenoids play a photoprotective role by dissipating unwanted excited states in antenna complexes (4, 5). It is well documented that carotenoids in purple phototrophic bacteria perform light-harvesting and structural roles, and the availability of carotenoidless mutants showed early on that carotenoids are essential for protection against oxygen radicals (6, 7). The present study demonstrates the mechanistic basis for photoprotection in photosynthetic bacteria using the purple bacterium Rhodobacter (Rba.) sphaeroides as a model. The photosynthetic complexes of this bacterium form interconnected membrane domains representing ∼4;000 BChl molecules (8-10). The membranes are found within the cell as hundreds of spherical intracytoplasmic membrane vesicles ∼50 nm in diameter (11). Light-harvesting LH2 complexes form the bulk...

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Section: Resultssupporting

confidence: 49%

mentioning

confidence: 71%

Section: Resultsmentioning

confidence: 99%

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Photoprotection in a purple phototrophic bacterium mediated by oxygen-dependent alteration of carotenoid excited-state properties

Šlouf

Chábera

Olsen³

et al. 2012

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

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“…3). A comparison of the uorescence excitation spectra showed that the eciency of Crt → BChla energy transfer decreases gradually from 90 to 35% along the series, very close to the values obtained by ultrafast absorption spectroscopy [28,29]. As the number of conjugated double bonds in…”

Section: Intracomplex Energy Transfermentioning

confidence: 88%

“…A series of LH1 complexes incorporating various Crts (neurosporene, spheroidene, lycopene, anhydrorhodovibrin and spirilloxanthin) was obtained, using the Crt exchange approach [28,29]. The correctness of LH1 assembly is conrmed by the high eciency of the intracomplex Crt → BChl singlet energy transfer (Fig.…”

Section: Intracomplex Energy Transfermentioning

confidence: 99%

Controlling Structural and Functional Features of Photosynthetic Antenna

Fiedor

Pilch

et al. 2012

Acta Phys. Pol. A

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In order to gain control over the assembly and functioning of photosynthetic antenna, we have developed methods to manipulate pigment composition of bacterial LH1 complexes via their reconstitution with modied bacteriochlorophylls or carotenoids, major photoactive cofactors of these antennae. In the present work we show how the reconstitution and pigment exchange approach is applied to control structural and functional parameters of LH1 and its subunits. The size of the subunits and the energy of the rst excited singlet state can be controlled via the use of detergent while the thermodynamics of LH1 formation can be modied using carotenoids and/or a co-solvent. Carotenoids aect the eciency of the intracomplex energy transfer, while the replacement of native bacteriochlorophyll a with its Ni-substituted analog allows one to control the excited state properties of LH1. These results show that LH1 is a very promising model system applicable for the design of bio-inspired device performing solar energy conversion.

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Quantum Chemical Description of Absorption Properties and Excited‐State Processes in Photosynthetic Systems

2011

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The theoretical description of the initial steps in photosynthesis has gained increasing importance over the past few years. This is caused by more and more structural data becoming available for light-harvesting complexes and reaction centers which form the basis for atomistic calculations and by the progress made in the development of first-principles methods for excited electronic states of large molecules. In this Review, we discuss the advantages and pitfalls of theoretical methods applicable to photosynthetic pigments. Besides methodological aspects of excited-state electronic-structure methods, studies on chlorophyll-type and carotenoid-like molecules are discussed. We also address the concepts of exciton coupling and excitation-energy transfer (EET) and compare the different theoretical methods for the calculation of EET coupling constants. Applications to photosynthetic light-harvesting complexes and reaction centers based on such models are also analyzed.

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Dependence of singlet-energy transfer on the conjugation length of carotenoids reconstituted into the LH1 complex from Rhodospirillum rubrum G9

Cited by 53 publications

References 17 publications

Photoprotection in a purple phototrophic bacterium mediated by oxygen-dependent alteration of carotenoid excited-state properties

Photoprotection in a purple phototrophic bacterium mediated by oxygen-dependent alteration of carotenoid excited-state properties

Controlling Structural and Functional Features of Photosynthetic Antenna

Quantum Chemical Description of Absorption Properties and Excited‐State Processes in Photosynthetic Systems

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