Variation in Electron Paramagnetic Resonance Signals of Photosynthetic Systems WTTH the Redox Level of Their Environment

Loach, Paul A.; Androes, G. M.; Maksim, Ann F.; Calvin, Melvin

doi:10.1111/j.1751-1097.1963.tb08901.x

Cited by 100 publications

(54 citation statements)

References 16 publications

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“…+550 mV (33), but no results were reported to indicate an association of the component with a primary reactant of Photosystem II. Since we have not made measurements of our light-induced change at physiological temperatures, the relation of the reported radical signal and our newly detected signal is not clear.…”

Section: Discussionmentioning

confidence: 90%

Detection of a Free Radical in the Primary Reaction of Chloroplast Photosystem II

Malkin

Bearden

1973

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

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Electron paramagnetic resonance (EPR) spectroscopy has revealed a new free-radical signal produced by illumination of spinach chloroplasts at 770K. This signal is observed only when an oxidant (ferricyanide) is added to the chloroplast suspension in the dark before illumination. The EPR signal is produced at 770K by illumination with 645-nm monochromatic light capable of activating Photosystem II but not with 715-nm illumination capable of activating Photosystem I. Furthermore, since the signal shows a relative increase in chloroplast fragments enriched in Photosystem II but is absent in chloroplast fragments enriched in Photosystem I, we conclude that this new EPR signal is associated with the primary photoact of Photosystem II in chloroplasts. On the basis of the measured EPR parameters (g = 2.0026 i 0.0002, linewidth = 8 G), it is suggested that the signal may be associated with the reaction-center chlorophyll of Photosystem II.The mechanism of oxygen evolution is one of the major unresolved problems inl chloroplast photosynthesis. Oxygen evolution has been found to )roceed more efficiently in short-wavelength light ( Chloroplast samples were placed in standard X-band quartz EPR tubes (3 mm i.d.) and illuminated for 30 sec at 770K directly in the EPR cavity with the apparatus described (20). Baird-Atomic interference filters (715 or 645 nm) of half-band width of 10 nm were used for the monochromatic illuminations. The incident light intensity on the sample was about 5 X 104 ergs cm-2 -sec-1. EPR spectra were recorded at 9.22

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Section: Discussionmentioning

confidence: 90%

Detection of a Free Radical in the Primary Reaction of Chloroplast Photosystem II

Malkin

Bearden

1973

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

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“…Conditions for growth of R. rubrum and preparation of the chromatophore fraction from whole cells have been described (4). Details for dissolution of chromatophores by the alkaline-urea-Triton method have also been given (1, 2).…”

Section: Methodsmentioning

confidence: 99%

“…At each field setting, the rate of change due to oxidation of the primary electron donor was subtracted from the total by conducting an identical measurement with a sample of chromatophores. In both cases, the samples absorbed all the light (880 4 10 nm) incident upon them. The shape and location data of the reduced radical, as shown in Fig.…”

Section: -R--1--w-t---1 1--1---t-7t-mentioning

confidence: 99%

The Question of the Primary Electron Acceptor in Bacterial Photosynthesis

Loach

Hall

1972

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

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An electrophoretic purification of Rhodospirillum rubrum photoreceptor subunits preparedby alkaline urea-detergent disruption is described. Completely active photoreceptor subunits with less than 0.30 eq of iron (or any Recent results from this laboratory (1, 2) have demonstrated that photosynthetic membrane fragments (chromatophores) of Rhodopseudomonas spheroides and Rhodospirillum rubrum can be quantitatively dissociated to yield active photoreceptor subunits. The procedure, in which chromatophores are treated with Triton X-100 and urea at high pH (AUT conditions), followed by sucrose density gradient centrifugation, causes a displacement of much of the phospholipid and a separation of about half of the protein originally present in the chromatophore membranes. The photoreceptor complex has a particle weight of about 100,000, contains most of its original complement of bacteriochlorophyll and carotenoid, and also retains high photochemical efficiency for the use of light absorbed by antenna carotenoids or bacteriochlorophyll. Iron was the only transition metal still present in the preparation at a high-enough concentration to have a direct role in the photochemical reaction. In the present report, we present data to show that iron is not required in these preparations for good photochemical activity (see also ref.3) and, therefore, probably does not function as the primary electron acceptor in these systems.The fact that transition metals do not play a role in the primary photochemical reaction would require that a second Abbreviations: AUT particles, the phototrap-containing fraction prepared by the combined alkaline urea-Triton X-100 method for membrane dissolution; AUT-e, electrophoretically-purified AUT particles; P865, the primary electron-donor molecule, characterized by a light-induced absorbance decrease at 865 nm. organic free-radical should be observable in these preparations, since the primary electron donor, a bacteriochlorophyll molecule, loses a single electron. In the case of the more intact membranous systems (e.g., chromatophores), it is well established that the only radical observed under the usual conditions of steady-state illumination is accounted for by the primary electron donor molecule (4-7). We also report here a newly observed EPR signal, which appears upon preparation of photoreceptor subunits from R. rubrum membrane particles. The molecule that gives rise to the signal has properties that would be expected of a primary electron acceptor. MATERIALS AND METHODSTriton X-100 is a product of Rohm and Haas, Philadelphia, Pa. All other chemicals were of at least reagent grade purity, and all solutions were made with deionized or deionized and distilled water.Conditions for growth of R. rubrum and preparation of the chromatophore fraction from whole cells have been described (4). Details for dissolution of chromatophores by the alkaline-urea-Triton method have also been given (1, 2). The original conditions (3% Triton X-100-6 M urea, pH 11.5) were modified by the addition of 1 ...

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“…(9) When chromatophore preparations are extracted with ethanol or acetone at various stages during the progress of such oxidation, the height of the bacteriochlorophyll peak at 770 mlJ (5) . .…”

Section: !mentioning

confidence: 99%

“…In certain bacterial chromatophores, such changes are accompanied by the production of unpaired electrons (9), and may be reversibly duplicated by careful treatment with such "one-electron" oxidants as hexachloroiridate{IV) or ferricyanide. (8) An interesting facet of such oxidations is the irreversible bleaching of the principal pigment which often occurs.…”

mentioning

confidence: 99%

Absorption Changes in Bacterial Chromatophores. Ii. A Newchlorophyll-Like Pigment From the Oxidation of Chromatophores Fromrhodospirillum Rubrum

Gould¹,

Kuntz²,

Calvin³

1964

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Variation in Electron Paramagnetic Resonance Signals of Photosynthetic Systems WTTH the Redox Level of Their Environment

Cited by 100 publications

References 16 publications

Detection of a Free Radical in the Primary Reaction of Chloroplast Photosystem II

Detection of a Free Radical in the Primary Reaction of Chloroplast Photosystem II

The Question of the Primary Electron Acceptor in Bacterial Photosynthesis

Absorption Changes in Bacterial Chromatophores. Ii. A Newchlorophyll-Like Pigment From the Oxidation of Chromatophores Fromrhodospirillum Rubrum

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