Triplet states in photosystem I of spinach chloroplasts and subchloroplast particles.

Frank, Harry A.; McLean, Mary Blackwell; Sauer, Kenneth

doi:10.1073/pnas.76.10.5124

Cited by 72 publications

(29 citation statements)

References 33 publications

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“…This demonstrates the primary photochemical activity of the preparation. The ZFS parameters calculated from this EPR spectrum agree, within experimental error, with those first reported by Frank et al (1979), and also with those found in this work using FDMR detected at Af > 700 nm (see below and Table 1). This is good evidence for the identity of the triplet state measured by FDMR at A e > 700 nm with 3p700, however, it cannot be regarded as conclusive as it is well established that there is relatively little variation in ZFS parameters between different forms of Chl a (Schaafsma 1982).…”

Section: Spectral Characterisation Of Cp1supporting

confidence: 79%

“…The 3p700 is generated by the radical pair (RP) mechanism, first observed in PSI by Frank et al (1979). It contains only the 82kD/83 kD heterodimer, which binds the heterogenous population of antenna Chl a and the primary electron donor P700 and electron acceptor A0, and has lost LHCI, the 730-735nm emitting light harvesting Chl a/bprotein (Kuang et al 1984), together with the smaller polypeptides present in larger PSI particles (Scheller et al 1989).…”

Section: Introductionmentioning

confidence: 99%

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Fluorescence detected magnetic resonance of the primary donor and inner core antenna chlorophyll in Photosystem I reaction centre protein: Sign inversion and energy transfer

Searle

Schaafsma

1992

Photosynth Res

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The Photosystem I reaction centre protein CP1, isolated from barley using polyacrylamide gel electrophoresis showed an EPR (Electron Paramgnetic Resonance) spectrum with the polarisation pattern AEEAAE, typical of the primary donor triplet state (3)P700, created via radical pair formation and recombination. (3)P700 could also be detected by Fluorescence Detected Magnetic Resonance (FDMR) at λf > 700 nm even in the presence of a large number of chlorophyll antennae. Its zero field splitting parameters, D=282.5×10(-4) cm(-1) and E=38.5×10(-4) cm(-1), were independent of the detection wavelength, and agreed with ADMR (Absorption Detected Magnetic Resonance) and EPR values. The signs of the (3)P700 D+E and D-E transitions were positive (increase in fluorescence intensity on applying a resonance microwave field). In contrast, in the emission band 685 < λf < 700 nm FDMR spectra with negative D+E and D-E transitions were detected, and the D value was wavelength-dependent. These FDMR results support an excitation energy transfer model for CP1, derived from time-resolved fluorescence studies, in which two chlorophyll antenna forms are distinguished, with fluorescence at 685 < λf < 700 nm (inner core antennae, F690), and λf > 700 nm (low energy antenna sites, F720), in addition to the P700. The FDMR spectrum in F690 emission can be interpreted as that of (3)P700, observed via reverse singlet excitation energy transfer and added to the FDMR spectrum of the antenna triplet states generated via intramolecular intersystem crossing. This would indicate that reversible energy transfer between F690 and P700 occurs even at 4.2 K.

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Section: Spectral Characterisation Of Cp1supporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Fluorescence detected magnetic resonance of the primary donor and inner core antenna chlorophyll in Photosystem I reaction centre protein: Sign inversion and energy transfer

Searle

Schaafsma

1992

Photosynth Res

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“…These particles were prepared as previously described [19]. In each case, the treated suspensions were combined with an equal amount of ethylene glycol, sealed in EPR tubes, and stored at 77°K.…”

Section: Methodsmentioning

confidence: 99%

Radical pair interactions in spinach chloroplasts

McCracken

Frank

Sauer

1982

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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“…This represents ϳ0. 33 3 Car/P700. Wild-type PS I complexes show a flash-induced absorbance change that represents less than 0.08 3 Car/P700 ϩ (data not shown), which would suggest an increased generation of 3 Car in PS I complexes from the menB rubA mutant.…”

Section: Flash-induced Absorbance Changes In the Near-ir And Uvmentioning

confidence: 99%

“…Bottom, at later times, the polarization pattern changes into a "late" triplet signal with a (E)/A/E/A/E/(A) pattern; the sample is PS I complexes from the menB rubA mutant with Q ϭ PQ-9. The experimental conditions are as above except for a different time integration window of 7-10 s. The signal is assigned to 3 Car populated via intersystem crossing-populated 3 Chl and represents an independent photocycle in the antenna system of PS I. by 3 Car as observed optically (27) or by EPR (32)(33)(34). The same kind of triplet polarization patterns and competing excitation trapping processes were also observed in a recent study of PS I with a Met to Leu mutation of the axial ligand to the Mg 2ϩ of the primary electron acceptor A 0 (21).…”

Section: Flash-induced Absorbance Changes In the Near-ir And Uvmentioning

confidence: 99%

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

Sakuragi

Zybailov

Shen

et al. 2005

Journal of Biological Chemistry

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A photosystem I (PS I) complex containing plastoquinone-9 (PQ-9) but devoid of F X , F B , and F A was isolated and characterized from a mutant strain of Synechococcus sp. PCC 7002 in which the menB and rubA genes were insertionally inactivated. In isolated PS I trimers, the decay of P700؉ measured in the near-IR and the decay of A 1 ؊ measured in the near-UV were found to be biphasic, with (averaged) room temperature lifetimes of 12 and 350 s. The decay-associated spectra of both kinetic phases are characteristic of the oxidized minus reduced difference spectrum of a semiquinone, consistent with charge recombination between P700؉ and PQ-9 ؊ . The amplitude of the flash-induced absorbance changes in both the near-IR and the near-UV show that approximately one-half of the A 1 binding sites are either empty or nonfunctional. A spin-polarized chlorophyll triplet is observed by time-resolved EPR, and it is attributed to the 3 P700 product of P700 ؉ A 0 ؊ charge recombination via the T 0 spin level in those PS I complexes that do not contain a functional quinone. In those A 1 sites that are occupied, the P700 ؉ Q ؊ polarization pattern indicates that PQ-9 is oriented in a similar manner to that in the menB mutant. When excess 9,10-anthraquinone is added in vitro, it displaces PQ-9 and occupies the A 1 binding site more readily than in the menB mutant. This can be explained by a greater accessibility to the A 1 site in the menB rubA mutant due to the absence of F X and the stromal ridge polypeptides. The relatively low binding affinity of 9,10-anthraquinone allows it to be readily removed from the A 1 site by washing. However, all A 1 sites are shown to bind napthoquinones with high affinity and thus are proven to be functionally competent in quinone binding. The ability to readily displace PQ-9 from the A 1 site makes the menB rubA mutant ideal for introducing novel quinones, particularly anthraquinones, into PS I.Photosystem I is a multisubunit, pigment-protein complex that is found in the membranes of plants, algae, and cyanobacteria and that mediates the light-induced transfer of electrons from plastocyanin/cytochrome c 6 to ferredoxin/flavodoxin. According to current understanding, light-induced charge separation results in the oxidation of the primary electron donor P700 (E m Ј ϩ430 mV), a chlorophyll a/aЈ heterodimer located on the luminal (inner) side of the membrane, and the reduction of the primary electron acceptor A 0 (E m Ј approximately Ϫ1000 mV), a chlorophyll a monomer located in the interior of the membrane. The electron is passed to A 1 (E m Ј approximately Ϫ800 mV), an alkyl-substituted menadione (2-methyl-1,4-naphthalenedione); to F X (E m Ј Ϫ705 mV), an interpolypeptide (4Fe-4S) cluster; and finally to F A (E m Ј Ϫ520 mV) and F B (E m Ј Ϫ580 mV), which are (4Fe-4S) clusters bound to the extrinsic subunit PsaC located on the stromal (cytoplasmic) side of the membrane. In most organisms, including Synechocystis sp. PCC 6803, the quinone in the A 1 site is phylloquinone (2-methyl-3-phytyl-1,4-naphtho...

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Triplet states in photosystem I of spinach chloroplasts and subchloroplast particles.

Cited by 72 publications

References 33 publications

Fluorescence detected magnetic resonance of the primary donor and inner core antenna chlorophyll in Photosystem I reaction centre protein: Sign inversion and energy transfer

Fluorescence detected magnetic resonance of the primary donor and inner core antenna chlorophyll in Photosystem I reaction centre protein: Sign inversion and energy transfer

Radical pair interactions in spinach chloroplasts

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

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