Anisotropic electron spin polarization of correlated spin pairs in photosynthetic reaction centers

Stehlik, D.; Bock, Christian; Petersen, Jan

doi:10.1021/j100341a084

Cited by 156 publications

(142 citation statements)

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“…The half-time of 200 ns determined for this reaction in the present work suggests that the striking change in the polarized EPR spectrum of PS I at room temperature during the first few hundred nanoseconds after excitation (review [26]), reflects the same reaction. This would be consistent with the interpretation that the spin-polarized signals at early times arise from P700+ and a quinone-type AT [13,27,28].…”

Section: Resultssupporting

confidence: 90%

Electron transfer from A⁻₁to an iron‐sulfur center witht_{= 200 ns at room temperature in photosystem I Characterization by flash absorption spectroscopy}

Brettel

1988

FEBS Letters

116

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Forward electron transfer in intact photosystem I particles from Synechococcus sp. at room temperature has been studied by flash absorption spectroscopy with a time resolution of 5 ns. A kinetic phase with I ,,2 = 200 ns was resolved and characterized by its absorption difference spectrum between 325 and 495 nm. This phase is attributed to electron transfer from the reduced redox center A, to an iron-sulfur center, probably F.. The difference spectrum for the reduction of A, is evaluated and the previously proposed identification of A, with vitamin K, is discussed.

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Section: Resultssupporting

confidence: 90%

Electron transfer from A⁻₁to an iron‐sulfur center witht_{= 200 ns at room temperature in photosystem I Characterization by flash absorption spectroscopy}

Brettel

1988

FEBS Letters

116

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“…In contrast to [8] no zero-filling and no filtering was performed in our studies. The numerical simulations of the experimental data were calculated using a program, based on the simulation program for transient EPR spectra [3].…”

Section: Methodsmentioning

confidence: 99%

“…These RPs have been investigated using transient EPR spectroscopy (for reviews see [I, 21). Due to the anisotropic nature of the interaction between the RP electrons with an external magnetic field and the spin-spin coupling within the RP, information about the geometric arrangement of the two involved cofactors can be derived from the transient spectra of the RP state [3]. For the analysis of the experimental spectra, the model of the correlated coupled RP (CCRP) [4, 51 has successfully been applied.…”

Section: Introductionmentioning

confidence: 99%

Pulsed EPR experiments on radical pairs in photosynthesis: Comparison of the donor‐acceptor distances in photosystem I and bacterial reaction centers

Zech

Lubitz

Bittl

1996

Ber Bunsenges Phys Chem

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Pulsed EPR spectroscopy is applied to the radical pairs P&Q, in bacterial reaction centers of Rhodobacter sphaeroides R-26 and P;&, ' in photosystem I from Synechococcus elongatus. For both radical pairs an outof-phase echo was observed showing a deep modulation as a function of the spacing between the two microwave pulses. From the modulation frequency the dipolar and isotropic couplings between the radical pair spins were derived. For the bacterial reaction centers a dipolar coupling of D = -121 FT was obtained, resulting in a distance of about 28.4 A between the electron spins of the radical pair. This value is in good agreement with the distance derived from the x-ray structure of Rhodobacter sphaeroides R-26. From the faster modulation in the PS I sample we obtained a dipolar coupling of D = -170 wT, indicating a distance of 25.4 A between the primary donor P,oo and the acceptor quinone A , . For both radical pairs, only a small isotropic coupling of J = 1 pT, consistent with transient EPR spectra, was found.

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“…Light-induced charge separation in all well characterized photosynthetic reaction centers (RCs) 1 proceeds via a common multistep electron transfer process to a stabilized, charge-separated radical pair state P ϩ Q Ϫ consisting of an oxidized (bacterio)chlorophyll donor and a reduced quinone acceptor (whether the green sulfur bacterial RC and the heliobacterial RC contain a quinone acceptor is still controversial). Two types of RCs can be distinguished according to the electron acceptors and electron transfer pathways subsequent to the first quinone acceptor.…”

Section: ؊ (253 ؎ 03 å) Is the Same As Between P700mentioning

confidence: 99%

“…For native PS I, simulations of the polarization patterns of P ϩ A 1 Ϫ (1,2,7,17) show that A 1 is oriented such that the carbonyl bonds of the phylloquinone head group are parallel to the vector joining P700 ϩ and A 1 Ϫ . Qualitatively, this orientation of the quinone is reflected in the emissive feature on the low field edge of the spectra shown in Figs.…”

Section: Fig 4 Photoaccumulated and Simulated Q-band Cw Epr Spectramentioning

confidence: 99%

Recruitment of a Foreign Quinone into the A1 Site of Photosystem I

Zybailov¹,

Est²,

Zech³

et al. 2000

Journal of Biological Chemistry

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Electron paramagnetic resonance (EPR) and electronnuclear double resonance studies of the photosystem (PS) I quinone acceptor, A 1 , in phylloquinone biosynthetic pathway mutants are described. Room temperature continuous wave EPR measurements at X-band of whole cells of menA and menB interruption mutants show a transient reduction and oxidation of an organic radical with a g-value and anisotropy characteristic of a quinone. In PS I complexes, the continuous wave EPR spectrum of the photoaccumulated Q ؊ radical, measured at Q-band, and the electron spin-polarized transient EPR spectra of the radical pair P700 ؉ Q ؊ , measured at X-, Q-, and W-bands, show three prominent features: (i) Q ؊ has a larger g-anisotropy than native phylloquinone, (ii) Q ؊ does not display the prominent methyl hyperfine couplings attributed to the 2-methyl group of phylloquinone, and (iii) the orientation of Q ؊ in the A 1 site as derived from the spin polarization is that of native phylloquinone in the wild type. Electron spin echo modulation experiments on P700 ؉ Q ؊ show that the dipolar coupling in the radical pair is the same as in native PS I, i.e. the distance between P700؉ and Q ؊ (25.3 ؎ 0.3 Å) is the same as between P700 ؉ and A 1 ؊ in the wild type. Pulsed electron-nuclear double resonance studies show two sets of resolved spectral features with nearly axially symmetric hyperfine couplings. They are tentatively assigned to the two methyl groups of the recruited plastoquinone-9, and their difference indicates a strong inequivalence among the two groups when in the A 1 site. These results show that Q (i) functions in accepting an electron from A 0 ؊ and in passing the electron forward to the iron-sulfur clusters, (ii) occupies the A 1 site with an orientation similar to that of phylloquinone in the wild type, and (iii) has spectroscopic properties consistent with its identity as plastoquinone-9.Light-induced charge separation in all well characterized photosynthetic reaction centers (RCs) 1 proceeds via a common multistep electron transfer process to a stabilized, charge-separated radical pair state P ϩ Q Ϫ consisting of an oxidized (bacterio)chlorophyll donor and a reduced quinone acceptor (whether the green sulfur bacterial RC and the heliobacterial RC contain a quinone acceptor is still controversial). Two types of RCs can be distinguished according to the electron acceptors and electron transfer pathways subsequent to the first quinone acceptor. A series of iron-sulfur clusters with electron transfer essentially perpendicular to the membrane characterize Type I RCs (PS I, green sulfur bacteria, and heliobacteria), whereas a second quinone acceptor Q B and electron transfer parallel to the membrane from the first quinone acceptor Q A characterize Type II RCs (PS II and the RC of purple bacteria). The first quinone is therefore the interface either between electron transfer involving organic cofactors and electron transfer involving iron-sulfur clusters (Type I) or between pure electron transfer and coupled electron/proton tr...

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Anisotropic electron spin polarization of correlated spin pairs in photosynthetic reaction centers

Cited by 156 publications

References 1 publication

Electron transfer from A⁻₁to an iron‐sulfur center witht_{= 200 ns at room temperature in photosystem I Characterization by flash absorption spectroscopy}

Electron transfer from A⁻₁to an iron‐sulfur center witht_{= 200 ns at room temperature in photosystem I Characterization by flash absorption spectroscopy}

Pulsed EPR experiments on radical pairs in photosynthesis: Comparison of the donor‐acceptor distances in photosystem I and bacterial reaction centers

Recruitment of a Foreign Quinone into the A1 Site of Photosystem I

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Anisotropic electron spin polarization of correlated spin pairs in photosynthetic reaction centers

Cited by 156 publications

References 1 publication

Electron transfer from A−1to an iron‐sulfur center witht= 200 ns at room temperature in photosystem I Characterization by flash absorption spectroscopy

Electron transfer from A−1to an iron‐sulfur center witht= 200 ns at room temperature in photosystem I Characterization by flash absorption spectroscopy

Pulsed EPR experiments on radical pairs in photosynthesis: Comparison of the donor‐acceptor distances in photosystem I and bacterial reaction centers

Recruitment of a Foreign Quinone into the A1 Site of Photosystem I

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Electron transfer from A⁻₁to an iron‐sulfur center witht_{= 200 ns at room temperature in photosystem I Characterization by flash absorption spectroscopy}

Electron transfer from A⁻₁to an iron‐sulfur center witht_{= 200 ns at room temperature in photosystem I Characterization by flash absorption spectroscopy}