Low-Temperature Optical and Resonance Raman Spectra of a Carotenoid Cation Radical in Photosystem II

Vrettos, John S.; Stewart, David; Paula, Julio C. de; Brudvig, Gary W.

doi:10.1021/jp991464q

Cited by 75 publications

(79 citation statements)

References 34 publications

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“…Taking G Х 2 nS (the largest conductance measured for Car with 9 double bonds under oxidizing potential) (Fig. 3a Middle) yields k et ϭ 5.6 ϫ 10 6 s Ϫ1 or ϭ 0.18 s. Both time scales are significantly smaller than that assumed for electron transfer from Q A Ϫ to P 680 ϩ via ␤-carotene in photosystem II (200 s to 1 ms) (1,30), indicating that the electron transfer is not limited by the transfer across the Car but more likely by other steps in the photoprotection mechanism. Additionally, it is likely that electron transfer in our system involves ballistic tunneling of many electrons as opposed to consecutive oxidation and reduction for the transfer of each electron.…”

Section: Discussionmentioning

confidence: 93%

“…In photosystem II reaction centers, Car participate in the ''side-path'' electron donation reactions for reduction of P 680 ϩ as part of the photoprotective system. The role of the Car is thought to be that of an electron carrier (1,2). It is believed that ␤-carotene in photosystem II is oxidized under illumination (1,2).…”

mentioning

confidence: 99%

“…The role of the Car is thought to be that of an electron carrier (1,2). It is believed that ␤-carotene in photosystem II is oxidized under illumination (1,2). To investigate whether Car oxidation is a prerequisite for electron transport in photosystem II photoprotection, we measured the conductivity and the length-dependence of the tunneling rate for single-Car molecules under potential control.…”

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confidence: 99%

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Conductance of a biomolecular wire

Visoly‐Fisher

Daie

Terazono

et al. 2006

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

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Carotenoids (Car) act as ''wires'' that discharge unwanted electrons in the reaction center of higher plants. One step in this ''side-path'' electron conduction is thought to be mediated by Car oxidation. We have carried out direct measurements of the conductance of single-Car molecules under potential control in a membrane-mimicking environment, and we found that when Car are oxidized conductance is enhanced and the electronic decay constant (␤) is decreased. However, the neutral molecule may already be conductive enough to account for observed electron transfer rates.carotenoid ͉ molecular electronics ͉ photosynthesis ͉ potential control ͉ single molecule P hotosynthetic systems are natural photoelectronic devices, integrating electronic and photonic elements in a protein scaffold. Understanding the role played by the different components is important both for understanding photosynthetic processes as well as for using them in artificial molecular electronic devices. Carotenoids (Car) in photosynthesis contribute to light harvesting, structural stabilization, and protection from photooxidation. In photosystem II reaction centers, Car participate in the ''side-path'' electron donation reactions for reduction of P 680 ϩ as part of the photoprotective system. The role of the Car is thought to be that of an electron carrier (1, 2). It is believed that ␤-carotene in photosystem II is oxidized under illumination (1, 2). To investigate whether Car oxidation is a prerequisite for electron transport in photosystem II photoprotection, we measured the conductivity and the length-dependence of the tunneling rate for single-Car molecules under potential control. Measuring electron transport under potential control allows us to simulate the redox environment of the Car under natural conditions and to relate our electronic measurements to its function in vivo.Single (neutral) Car polyenes are much more conductive than alkanes of equivalent length because of their conjugated -electron system (3-5). We and others (6-9) have shown that the conductivity of redox-active single molecules can be regulated by changes in the molecule's oxidation state. Here, we have extended our experimental methods to work in a water-and oxygen-free environment that mimics the conditions found in cell membranes. In this way, we hope to understand one of the roles of Car in photosynthesis and to explore their role as gatable electronic components. Finding such components remains a challenge to date (10).Single-molecule electron transport measurements under potential control were carried out by following the method developed by Xu and Tao (6, 11), for which a scanning tunneling microscope (STM) is used with a partially insulated probe to enable measurements in a conductive electrolyte, which is required for maintaining potential control. A scheme of the experimental setup is shown in Fig. 1 (see also the supporting information, which is published on the PNAS web site). Photosystem II is a transmembrane protein complex, so the surrounding environment o...

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Section: Discussionmentioning

confidence: 93%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Conductance of a biomolecular wire

Visoly‐Fisher

Daie

Terazono

et al. 2006

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

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“…12 Carotenoids also may act as stabilizers of protein structure and facilitators of the assembly of pigment-protein complexes, [13][14][15] as regulators of energy flow, 6,[15][16][17][18][19][20][21] or as redox cofactors. [22][23][24][25] The most well-known naturally occurring carotenoid, -carotene, is a C 40 hydrocarbon with terminal isoprenoid rings and eleven π-electron conjugated carbon-carbon double bonds. Other naturally occurring carotenoids often contain functional group substitutions along the polyene chain and on the isoprenoid terminal rings.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic and Photochemical Properties of Open-Chain Carotenoids

et al. 2002

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The spectroscopic properties of open-chain, all-trans-C 30 carotenoids having seven, eight and nine π-electron conjugated carbon-carbon double bonds were studied using steady-state absorption, fluorescence, fluorescence excitation and time-resolved absorption spectroscopy. These diapocarotenes were purified by high performance liquid chromatography (HPLC) prior to the spectroscopic experiments. The fluorescence data show a systematic crossover from dominant S 1 f S 0 (2 1 A g f 1 1 A g ) emission to dominant S 2 f S 0 (1 1 B u f 1 1 A g ) with increasing extent of conjugation. The low temperatures facilitated the determination of the spectral origins of the S 1 f S 0 (2 1 A g f 1 1 A g ) emissions, which were assigned by Gaussian deconvolution of the experimental line shapes. The lifetimes of the S 1 states of the molecules were measured by transient absorption spectroscopy and were found to decrease as the conjugated chain length increases. The energy gap law for radiationless transitions is used to correlate the S 1 energies with the dynamics. These molecules provide a systematic series for understanding the structural features that control the photochemical properties of open-chain, diapocarotenoids. The implications of these results on the roles of carotenoids in photosynthetic organisms are discussed.

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“…The Chl Z cation is re-reduced by Cyt b 559, which, in turn, is reduced by reduced plastoquinone. Recent evidence also suggests that a ␤-carotene (␤-Car) may participate in this PSII electron transfer cycle between Chl Z and P680 or directly reduce P680 ϩ (26)(27)(28)(29)(30)(31)(32)(33). The Chl Z cycle has been proposed to reduce photoinhibitory damage by facilitating the oxidation of overreduced quinone electron acceptors and reduction of long-lived P680 ϩ states (25,34).…”

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confidence: 99%

Functional asymmetry of photosystem II D1 and D2 peripheral chlorophyll mutants of Chlamydomonas reinhardtii

Wang

Gosztola

Ruffle

et al. 2002

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

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The peripheral accessory chlorophylls (Chls) of the photosystem II (PSII) reaction center (RC) are coordinated by a pair of symmetryrelated histidine residues (D1-H118 and D2-H117). These Chls participate in energy transfer from the proximal antennae complexes (CP43 and CP47) to the RC core chromophores. In addition, one or both of the peripheral Chls are redox-active and participate in a low-quantum-yield electron transfer cycle around PSII. We demonstrate that conservative mutations of the D2-H117 residue result in decreased Chl fluorescence quenching efficiency attributed to reduced accumulation of the peripheral accessory Chl cation, Chl Z ؉ . In contrast, identical symmetry-related mutations at residue D1-H118 had no effect on A mong the photosynthetic organisms, there are two different, quinone-type photosynthetic reaction centers (RCs): the oxygenic type present in chloroplasts and cyanobacteria (photosystem II, PSII) and the nonoxygenic type (bacterial reaction center, BRC) as typified by that in purple-sulfur photosynthetic bacteria (for reviews, see refs. 1 and 2). In 1984, the crystal structure of the Rhodopseudomonas viridis BRC was determined at 3-Å resolution by Deisenhofer et al. (3). It soon was recognized that the L and M polypeptides of the BRC had substantial amino acid sequence similarity with the PSII D1 and D2 proteins, respectively. Early models of the D1 and D2 proteinfolding topologies indicated that the PSII D1 and D2 polypeptides were structurally analogous to the L and M subunits (3-8). These models of the PSII RC polypeptides and their associated cofactors were verified by electron and x-ray diffraction of twoand three-dimensional PSII crystals (9-12). Recently, a 3.8-Å resolution structure of the oxygen-evolving PSII complex from Synechecoccus elongatus was determined (13).The PSII RC has six chlorophylls (Chls), two pheophytins (Pheos), two quinones, and one cytochrome b 559 (Cyt b 559 ) heme (8, 13). Significantly, the PSII RC has two additional Chls, relative to the BRC. Site-directed mutagenesis and spectroscopic studies demonstrated that the additional pair of Chls present in PSII is coordinated by a pair of conserved and C 2 symmetryrelated histidine residues (D1-H118 and D2-H117, Chlamydomonas reinhardtii nomenclature) (14-20). Unlike the four Chls and two Pheos involved in primary charge separation, the additional pair of Chls present in the PSII RC is located on the periphery of D1 and D2 polypeptides.Biophysical evidence for the involvement of the peripheral Chls in energy transfer first was obtained from analysis of P680 oxidation kinetics by Schelvis et al. (14). They observed a Ϸ30-ps P680 oxidation lifetime component, which they attributed to energy transfer from a Chl monomer to P680. Based on a Förster mechanism (21) for energy transfer, they calculated that the distance between the peripheral Chl and P680 was 30 Å, a distance confirmed by the recent PSII crystal structure. A similar distance relationship also was predicted on the basis of Chl fluorescence decay kine...

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Low-Temperature Optical and Resonance Raman Spectra of a Carotenoid Cation Radical in Photosystem II

Cited by 75 publications

References 34 publications

Conductance of a biomolecular wire

Conductance of a biomolecular wire

Spectroscopic and Photochemical Properties of Open-Chain Carotenoids

Functional asymmetry of photosystem II D1 and D2 peripheral chlorophyll mutants of Chlamydomonas reinhardtii

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