Primary processes in Photosystem I. Identification and decay kinetics of the P-700 triplet state

Sétif, Pièrre; Quaegebeur, Jean-Pierre; Mathis, Paul

doi:10.1016/0005-2728(82)90174-8

Cited by 27 publications

(7 citation statements)

References 26 publications

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“…The second one of these redox states corresponds probably to a fast sub-/as recombination between P700* and Ao which has been observed in CP1 particles containing only the acceptor A0 [12]. This back reaction induces the formation of some P700 triplet state which decays at 10K with an approximate lifetime of 0.Sms [5,14,15,18]. These properties raise the possibility that there exists another intermediate electron acceptor between A 0 and A1.…”

Section: Discussionmentioning

confidence: 84%

Photosystem I photochemistry: A new kinetic phase at low temperature

Sétif¹,

Mathis²

1986

Photosynth Res

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A new phase of charge recombination between the oxidized primary electron donor of photosystem I (P700(+)) and a reduced acceptor has been detected by flash absorption spectroscopy in PS I particles at low temperature. It occurs under highly reducing conditions (the secondary electron acceptors FA and FB and one or possibly two 'more primary' acceptors being prereduced) with a t1/2 of about 20 μs between 10 and 80 K.

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Section: Discussionmentioning

confidence: 84%

Photosystem I photochemistry: A new kinetic phase at low temperature

Sétif¹,

Mathis²

1986

Photosynth Res

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“…Illumination then generates the radical pair P7oo + A^ that decays to P7oo T A 0 . This decay as measured optically, however, is much faster than the ESP lifetime of 5 /is (Setif, Quaegebeur & Mathis, 1982). This suggests that the polarized spectra displayed in Fig.…”

Section: Low-temperature Experiments Soon After the Initial Work Bymentioning

confidence: 79%

“…In recent years the kinetic parameters of P T in the plant photosystems 1 and 2 and in the photosystem of green bacteria have also been accurately determined (Table zb), either with EPR (PS 1: Gast et al 1983;Setif et al 1982; green sulphur bacteria: Swarthoff et al 1981 a; or with Absorbance Detected Magnetic Resonance in zero field (ADMR, Den Blanken & Hoff, 1982) (PS 1: Den Blanken & Hoff, 1983c;PS 2: Den Blanken et al 1983a;green bacteria: Den Blanken et al 1983 c;Vasmel et al 1984). In addition, the ADMR technique has permitted the recording of highly resolved singlet-minus-triplet absorbance difference spectra for photosynthetic bacteria Den Blanken et al 1983 c;Den Blanken, Jongenelis & Hoff, 1983;Vasmel et al 1984), PS 1 (Den Blanken & Hoff, 1983 c) and PS 2 .…”

Section: Three-electron Spin Calculationsmentioning

confidence: 99%

Electron spin polarization of photosynthetic reactants

Hoff

1984

Quart. Rev. Biophys.

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Photosynthesis is the conversion of the quantum energy of light into the chemical energy of complex organic molecules and organized cellular structures in plants and in some bacteria. The processes of photosynthesis span the time domain of subpicoseconds to the millennia of slow-growing trees, its study brings together such diverse disciplines as photophysics, biochemistry, botany and ecology. In the last few decades tremendous progress has been made in understanding the multivarious chemical reactions that ultimately lead to the fixation of carbon dioxide into organic substance, yet the basic mechanism underlying the conversion of photon energy into chemical energy still remains very much an enigma. These so-called primary reactions which transduce the excitation energy of excited chlorophyll pigments into the potential energy of stabilized, separated charges on electron donor and electron acceptor molecules have been studied with a variety of physical techniques, among which fast optical spectroscopy and electron paramagnetic resonance (EPR) are prominent. This review will highlight one intriguing aspect of EPR, namely that of electron spin polarization (ESP).† It will be shown that ESP of photosynthetic primary reactants offers a unique tool to gain insight in the electrostatic and magnetic interactions that make photosynthesis work. Moreover, it will become apparent that ESP in photosynthesis has several unique traits not (yet) found in ESP of photochemical reactions in vitro. As such, it may serve as a paradigma of ESP phenomena and will present an absorbing spectacle also for EPR spectroscopists outside photosynthesis.

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“…Illumination by 455 nm LED light induces the maximal absorbance changes that can be induced by visible actinic light due to an irreversible charge separation in a fraction of the PS I complexes. 30 , 31 Excitation with 50 flashes of a Xe-flash lamp or white light from a tungsten halogen lamp gives always the same maximum absorbance change as with 455 nm LED light. To determine the relative yield of P700 +• formation in PS I of different organisms at different excitation wavelengths and temperatures, the absolute values of the amplitudes at 691 and 703 nm were added and divided by the maximum value after irradiation with visible actinic light calculated in the same way.…”

Section: Resultsmentioning

confidence: 97%

“…The absorbance difference spectra (light-minus-dark) are attributed to the stable formation of P700 +• F A – • and P700 +• F B – • . It is known from studies of the heterogeneity of electron transfer reactions in PS I at low temperature 30 , 31 that in one fraction of the PS I complexes, an irreversible charge separation due to the stable formation of P700 +• F A/B –• takes place, whereas in the other fraction forward electron transfer to the terminal iron–sulfur clusters F A/B – • is completely blocked at cryogenic temperatures. 31 In this fraction, the charge separation is reversible at low temperature and can be attributed to the formation and decay of P700 +• A 1 –• and P700 +• F X –• , respectively.…”

Section: Methodsmentioning

confidence: 99%

Long-Wavelength Limit of Photochemical Energy Conversion in Photosystem I

et al. 2014

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In Photosystem I (PS I) long-wavelength chlorophylls (LWC) of the core antenna are known to extend the spectral region up to 750 nm for absorbance of light that drives photochemistry. Here we present clear evidence that even far-red light with wavelengths beyond 800 nm, clearly outside the LWC absorption bands, can still induce photochemical charge separation in PS I throughout the full temperature range from 295 to 5 K. At room temperature, the photoaccumulation of P700+• was followed by the absorbance increase at 826 nm. At low temperatures (T < 100 K), the formation of P700+•FA/B–• was monitored by the characteristic EPR signals of P700+• and FA/B–• and by the characteristic light-minus-dark absorbance difference spectrum in the QY region.P700 oxidation was observed upon selective excitation at 754, 785, and 808 nm, using monomeric and trimeric PS I core complexes of Thermosynechococcus elongatus and Arthrospira platensis, which differ in the amount of LWC. The results show that the LWC cannot be responsible for the long-wavelength excitation-induced charge separation at low temperatures, where thermal uphill energy transfer is frozen out. Direct energy conversion of the excitation energy from the LWC to the primary radical pair, e.g., via a superexchange mechanism, is excluded, because no dependence on the content of LWC was observed. Therefore, it is concluded that electron transfer through PS I is induced by direct excitation of a proposed charge transfer (CT) state in the reaction center. A direct signature of this CT state is seen in absorbance spectra of concentrated PS I samples, which reveal a weak and featureless absorbance band extending beyond 800 nm, in addition to the well-known bands of LWC (C708, C719 and C740) in the range between 700 and 750 nm. The present findings suggest that nature can exploit CT states for extending the long wavelength limit in PSI even beyond that of LWC. Similar mechanisms may work in other photosynthetic systems and in chemical systems capable of photoinduced electron transfer processes in general.

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Primary processes in Photosystem I. Identification and decay kinetics of the P-700 triplet state

Cited by 27 publications

References 26 publications

Photosystem I photochemistry: A new kinetic phase at low temperature

Photosystem I photochemistry: A new kinetic phase at low temperature

Electron spin polarization of photosynthetic reactants

Long-Wavelength Limit of Photochemical Energy Conversion in Photosystem I

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