Primary photochemistry and electron transport in Rhodospirillum rubrum

Loach, Paul A.; Sekura, Diane L.

doi:10.1021/bi00847a029

Cited by 69 publications

(44 citation statements)

References 32 publications

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“…13A~ In Chromatiwn a somewhat higher potential of 0.49 V for P870 has been reported by Cusanovich, BarL~ch and Kamen (1968). Loach and Sekura (1967) showed that the decay kinetics of the photoinduced absorption changes owing to P870 are identical to those of the EPR signal.. further kinetic and stoichiometric evidence supporting the identification of P870+ as oxidized BChl and responsible for the EPR signal was reported by Bolton, Clayton and Reed (1969) and by McElroy, Feher and ~huzerall (1969). Fig.…”

Section: 3 Trapping Times Deduced From Fluorescence Measurementssupporting

confidence: 55%

“…At room temperature the quantum yields are close to unity for both the P870 change (Leach and Sekl1ra, 1968;Parson, I 1968;Beugl ing, 1968;Bolton et al, 1969;Clayton, Fleming and Szuts, 1972;Clayton, Szuts and Fleming, 1972;Slooten, 1972) and for the EPR I signal (Loach and Walsh, 1969;Weaver and Weaver, 1969;Loach and Hall, 1972) 'for chromatophores and reaction center preparations. 1he quantum yield of the P87p bleaching is changed hardly at all c..t l°K (Clayton, !…”

Section: 3 Trapping Times Deduced From Fluorescence Measurementsmentioning

confidence: 86%

“…Subsequently Loach and Hall (1972), working with a preparation of photoreceptor subtmi ts from ~ rubrum containing active P870 but only 0.30 equivalents of Fe per reaction center, observed a rather narrow EPR signal at g = 2. 0050 which was kinetically similar to the BChl +signal at g = 2.0025.…”

Section: ·Primary Electron Acceptorsmentioning

confidence: 99%

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Primary Events and the Trapping of Energy

Sauer¹

1975

Energetics of Photosynthesis

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Section: 3 Trapping Times Deduced From Fluorescence Measurementssupporting

confidence: 55%

Section: 3 Trapping Times Deduced From Fluorescence Measurementsmentioning

confidence: 86%

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Primary Events and the Trapping of Energy

Sauer¹

1975

Energetics of Photosynthesis

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“…The unpaired spin is delocalized over a special pair of bacteriochlorophyll molecules. That the signal is produced in the primary quantum conversion reaction in which the special pair functions as the primary donor is suggested by the measured quantum yield for the signal production (Loach and Walsh, 1969) and for the oxidation of P870 (Loach and Sekura 1968;Wraight and Clayton, 1973). The measured values are near unity.…”

Section: Primary Donormentioning

confidence: 96%

“…It is well established for most bacteria that a c-type cytochrome is the secondary component which donates electrons to the oxidized primary donor 617 I 1 1 1 1 1 1 (Duysens, 1954;Chance and Smith, 1955;Olson and Chance, 1960;Clayton, 1962;Morita et al, 1965;Loach and Sekura, 1968;Cusanovich r't al., 1968). In addition, it has been shown that h-type cytochromes (Nishimura and Chance, 1963;Ke and Ngo, 1967;Dutton and Jackson, 1972;Evans and Crofts, 1974;Knaff and Buchanan, 1975;Prince and Dutton, 1975), iron-sulfur proteins (Shanmugan and Arnon, 1972) and ubiquinone (Clayton, 1962a;Clayton and Straley, 1972;Slooten, 1972;Romijn and Amesz, 1975) are involved in bacterial electron transport reactions.…”

Section: Introductionmentioning

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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Inhibition of the Primary Photochemical Events in Rhodospirillum Rubrum by Ubiquinone Analogues

Bering

Bustamante

Loach

1981

Israel Journal of Chemistry

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Twenty‐one quinone compounds have been tested for their ability to inhibit the primary photochemical events when added to R. rubrum chromatophores. This was determined by measuring their effect on the light‐induced absorbance change at 605 nm and their ability to quench the variable portion of fluorescence (Fv). Benzoquinone structures with one or more bromine or iodine substituents and a bulky group (isopropyl, t‐butyl, n‐hexyl) were particularly effective inhibitors. The most potent of these were 2,3,5‐tribromo‐6‐n‐hexyl‐1,4‐benzoquinone and 2,3‐diiodo‐5‐t‐butyl‐1,4‐benzoquinone which caused 50% inhibition at less than μM quantities (or about 5 to 10 fold above the phototrap concentrations). From control experiments with egg yolk phosphatidylcholine liposomes containing bacteriochlorophyll, it was shown that although the effective inhibitors also quenched fluorescence when added to this model system, quenching depended on the viscosity of the bilayer and was not very sensitive to structural parameters. In the in vivo system, phototrap activity was inhibited at 77 K to the same extent as room temperature, indicating diffusion was not important. In the control experiments with liposomes, the concentration for which 50% quenching was observed by 2,5‐dibromo‐3,6‐dimethyl‐1,4‐benzoquinone and 2,3,5‐tribromo‐6‐n‐hexyl‐1,4‐benzoquinone only differed by two fold whereas in the chromatophore system, the difference was over 1000 fold; no effect was seen in vivo by the former compound and the latter was the most effective. It is suggested that most of the instantaneous fluorescence (Fo) is from a bacteriochlorophyll component(s) which does not communicate with the reaction center and a higher concentration of added quinone is required before this pigment fluorescence is quenched.

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Primary photochemistry and electron transport in Rhodospirillum rubrum

Abstract: Fl- .photoxidation, a quantum yield of 0.95 ± 0.05 was determined for production of the primary oxidized species called P 870 or P0.44. The extent of the cytochrome c photoxidation could be significantly increased by adding horse heart ferrocytochrome c and 1.5%

Cited by 69 publications

References 32 publications

Primary Events and the Trapping of Energy

Primary Events and the Trapping of Energy

A Survey of Epr Investigations of Bacterial Photosynthesis

Inhibition of the Primary Photochemical Events in Rhodospirillum Rubrum by Ubiquinone Analogues

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