On the question of the primary acceptor in bacterial photosynthesis: Manganese substituting for iron in reaction centers of Rhodopseudomonas spheroides R-26

Fehér, G.; Isaacson, R. A.; McElroy, James D.; Ackerson, L.C.; Okamura, M. Y.

doi:10.1016/0005-2728(74)90104-2

Cited by 65 publications

(33 citation statements)

References 7 publications

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“…Following the light excitation, the EPR signals in Native and Quintuple mutant RCs decayed with different kinetics. Following the highest intensity illumination (I = 0.1 W/cm 2 ), the majority of the signal in the native RC ( (57,59). A minor component (see arrow Fig.…”

Section: Kinetics Of Charge Separation and Recombination In Native Anmentioning

confidence: 99%

Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

et al. 2006

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The reaction center (RC) from Rhodobacter sphaeroides captures light energy by electron transfer between quinones Q A and Q B , involving a conformational gating step. In this work, conformational states of D +• Q B −• were trapped (80K) and studied using EPR spectroscopy in mutant RCs that lack Q A in which Q B was reduced by the bacteriopheophytin along the B-branch. In mutant RCs frozen in the dark, a light induced EPR signal due to D +• Q B −• formed in 30% of the sample with low quantum yield (0.2%-20%) and decayed in 6 s. A small signal with similar characteristics was also observed in native RCs. In contrast, the EPR signal due to D + Q B − in mutant RCs illuminated while freezing formed in ~ 95% of the sample that did not decay (τ >10 7 s) at 80K. In all samples, the observed gvalues were the same (g=2.0026) indicating that all active Q B −• was located in a proximal conformation coupled with the non-heme Fe 2+ . We propose that before electron transfer at 80K, the majority (~70%) of Q B , structurally located in the distal site, cannot be stably reduced, while the minor ( can be considered to be the initial and final states along the reaction coordinate for conformationallygated electron transfer.

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Section: Kinetics Of Charge Separation and Recombination In Native Anmentioning

confidence: 99%

Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

et al. 2006

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“…To reconcile the UQ data with ESR evidence of an iron compound, a complex of iron-ubiquinone (Fe-UQ), Em = -50 mv, is generally considered to be a primary electron acceptor (9)(10)(11).…”

mentioning

confidence: 99%

Primary charge separation in bacterial photosynthesis: oxidized chlorophylls and reduced pheophytin.

Fajer¹,

Brune²,

Davis³

et al. 1975

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

287

173

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Bacteriopheophytin, the magesium-free base of bacteriochlorophyll, undergoes reversible one-electron reduction in organic solvents to yield an anionic free radical with characteristic optical and electron spin resonance spectra. The which was pumped away to codistill water, and the pigment was dried under reduced pressure (10-3 Pa) for several hours. RESULTSThe anion radical of bacteriopheophytin BPh exhibits a reversible, one electron, halfwave reduction potential E1/2 of -0.58 against NHE in CH2Cl2.

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“…Using chromatophores or sub-chromatophores of Chromatium D Dutton and Leigh, 1973), or reaction centers from R. spheroides Feher et al, 1974). Evans et al (1974) confirmed the photoproduction of the g = 1.82 line at temperatures less than 30 K in Chromatium chromatophores.…”

Section: Primary Acceptormentioning

confidence: 98%

“…However, the amplitude of the g = 2.0044 signal was non-reversibly increased when the whole cells were illuminated at 77 K as were two other signals with approximate g-values of 1.8 and 6.0. Several groups Bolton and Cost, 1973;Feher et al, 1974;Loach, 1975) have suggested that the primary acceptor is a complex between iron and ubiquinone. In fact, Feher et a/.…”

Section: Primary Acceptormentioning

confidence: 99%

A Survey of Epr Investigations of Bacterial Photosynthesis

Corker

1976

Photochem & Photobiology

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Abstract-Investigations in which EPR has been used as a probe of the mechanism of the primary quantum conversion reaction and/or electron transport reactions in bacterial photosynthesis are surveyed. These investigations include studies of whole cell organisms and simpler sub-cellular preparations, chromatophores and bacteriochlorophyll-protein complexes.Electron paramagnetic resonance studies have successfully demonstrated that the primary donor of the photosynthetic, photochemical reaction involves a dimer of bacteriochlorophyll, generally referred to as P870. P870 is photochemically oxidized to a cation radical which exhibits a g = 2.0025 EPR signal. Comparative studies of the time behaviour of this signal in whole cells and in sub-cellular preparations show that electron flow in the whole cells is substantially different than in the cell-free systems.The primary acceptor molecule of the photochemical reaction has not been conclusively identified. When it is photochemically reduced, it exhibits a broad EPR absorbance centered at g = 1.8 observable only at low temperatures. This signal involves an iron atom and a quinone molecule. Two possible identifications of the species responsible for the g = 1.8 signal are an iron-quinone complex and an iron-sulfur protein. The latter identification would require that one primary acceptor function for two primary donors and that the removal of a tightly held quinone alter the integrity of the system so as to inhibit the photochemistry.When the primary acceptor is chemically reduced, a photo-induced, polarized triplet EPR spectrum is detected. Both absorption and emission lines arq observed as if only one substate (m = 0) of the triplet manifold is populated. The zero field parameters of the triplet spectrum suggest that the triplet is formed through a decay of a biradical, not through an optical singlet to triplet transition.Low temperature EPR studies of photosynthetic preparations which had been poised at room temperature by subjecting the preparations to different redox potentials and/or dark adaptation and illumination show the presence of a number of light-influenced, EPR active components. The spectral characteristics of these components are indicative of iron-heme (both low and high-spin forms) and iron-sulfur (both oxidized and reduced) proteins and at least one other organic free radical distinct from P870'. The spectra varied for different strains of bacteria. Also, some of the signals detected in the whole cell organism were not detected in cell free preparations and the kinetics of the light influenced signal amplitudes were different in the whole cells than in chromatophores.

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On the question of the primary acceptor in bacterial photosynthesis: Manganese substituting for iron in reaction centers of Rhodopseudomonas spheroides R-26

Cited by 65 publications

References 7 publications

Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

Primary charge separation in bacterial photosynthesis: oxidized chlorophylls and reduced pheophytin.

A Survey of Epr Investigations of Bacterial Photosynthesis

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On the question of the primary acceptor in bacterial photosynthesis: Manganese substituting for iron in reaction centers of Rhodopseudomonas spheroides R-26

Cited by 65 publications

References 7 publications

Trapped Conformational States of Semiquinone (D+•QB-•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

Trapped Conformational States of Semiquinone (D+•QB-•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

Primary charge separation in bacterial photosynthesis: oxidized chlorophylls and reduced pheophytin.

A Survey of Epr Investigations of Bacterial Photosynthesis

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Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers