Primary Charge Separation in Photosystem I: A Two-Step Electrogenic Charge Separation Connected with P700+A0- and P700+A1- Formation

Hecks, Birgit; Wulf, Karsten; Breton, Jacques; Leibl, Winfried; Trissl, H.‐W.

doi:10.1021/bi00195a001

Cited by 75 publications

(53 citation statements)

References 46 publications

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“…The solid curve in Figure 4 represents the best fit of Equations (1) and (2) for 30 ps flashes to the ps-data with the fit parameters ka = (2.5 ps) -1 and/3 = 1.0, yielding a = 4.8. Also in this preparation P-700 and P-700 + quench equally strongly (Hecks et al 1994). …”

Section: Photosystem I Membranes From Cyanobacteriamentioning

confidence: 54%

Competition between annihilation and trapping leads to strongly reduced yields of photochemistry under ps-flash excitation

Wulf

Trissl

1996

Photosynth Res

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Excitation of photosynthetic systems with short intense flashes is known to lead to exciton-exciton annihilation processes. Here we quantify the effect of competition between annihilation and trapping for Photosystem II, Photosystem I (thylakoids from peas and membranes from the cyanobacterium Synechocystis sp.), as well as for the purple bacterium Rhodospirillum rubrum. In none of the cases it was possible to reach complete product saturation (i.e. closure of reaction centers) even with an excitation energy exceeding 10 hits per photosynthetic unit. The parameter α introduced by Deprez et al. ((1990) Biochim. Biophys. Acta 1015: 295-303) describing the competition between exciton-exciton annihilation and trapping was calculated to range between ≈4.5 (PS II) and ≈6 (Rs. rubrum). The rate constants for bimolecular exciton-exciton annihilation ranged between (42 ps)(-1) and (2.5 ps)(-1) for PS II and PS I-membranes of Synechocystis, respectively. The data are interpreted in terms of hopping times (i.e. mean residence time of the excited state on a chromophore) according to random walk in isoenergetic antenna.

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Section: Photosystem I Membranes From Cyanobacteriamentioning

confidence: 54%

Competition between annihilation and trapping leads to strongly reduced yields of photochemistry under ps-flash excitation

Wulf

Trissl

1996

Photosynth Res

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“…The present work supplements electrical measurements that are based on the light-gradient method (14,22). An early study on pea chloroplasts was restricted to the time window between 35 ps and 60 ns (the RC discharge time constant of the capacitative measuring cell).…”

Section: Discussionmentioning

confidence: 87%

“…PCC 6803, two phases were resolved in the rise of the photovoltage signal. These were assigned to the formation of the state P700+A-(22 ps) and to the further electron transfer from Ao to A1 (50 ps) (22). The lack of slower electrogenic components in ref.…”

Section: Discussionmentioning

confidence: 98%

Electrogenic light reactions in photosystem I: resolution of electron-transfer rates between the iron-sulfur centers.

Sigfridsson

Hansson

Brzezinski

1995

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

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Flash-induced voltage changes (electrogenic events) in photosystem I particles from spinach, oriented in a phospholipid layer, have been studied at room temperature on a time scale ranging from 1 ,us to several seconds. A phospholipid layer containing photosystem I particles was adsorbed to a Teflon film separating two aqueous compartments. Voltage changes were measured across electrodes immersed in the compartments. In the absence of added electron donors and acceptors, a multiphasic voltage increase, associated with charge separation, was followed by a decrease, associated with charge recombination. Several kinetic phases were resolved: a rapid (<1 ,us) increase, ascribed to electron transfer from the primary electron donor P700 to the ironsulfur electron acceptor FB, was followed by a slower, biphasic increase with time constants of 30 and 200 ,is. The 30-,us phase is assigned to electron transfer from FB to the ironsulfur center FA. The voltage decrease had a time constant of 90 ms, ascribed to charge recombination from FA to P700. Upon chemical prereduction of FA and FB the 30-and 200-,us phases disappeared and the decay time constant was accelerated to 330 pus, assigned to charge recombination from the phylloquinone electron acceptor (A1) or the iron-sulfur center Fx to P700.The photosystem I (PSI) reaction center is a membrane-bound protein complex, which converts light energy to redox energy.The spinach complex consists of 2 large ("80 kDa) and at least 10 smaller (5-20 kDa) subunits, which bind a number of cofactors associated with the conversion process. The absorption of light by one of -200 antenna chlorophyll molecules is followed by a rapid migration of the excitation energy to the chlorophyll primary electron donor, P700, and an electron transfer is then brought about between P700 and the chlorophyll primary electron acceptor Ao. The sequence and kinetics of the electron-transfer reactions between the different cofactors have been investigated by a number of spectroscopic techniques, including flash-induced optical and electron paramagnetic resonance (EPR) spectroscopy. The details of the electron-transfer reactions between the Fe-S centers are, however, largely unknown. This is so because the optical spectra of the Fe-S centers are nearly identical and, although they can be distinguished with EPRThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. spectroscopy, such studies can be made only at low temperatures (<40 K) since their EPR spectra are too broad at higher temperatures.In this study, we have used a different approach. PSI particles were oriented in a phospholipid layer adsorbed to a Teflon film, and light-induced electrogenic events were measured. This technique has previously been used with bacteriorhodopsin (5) and with reaction centers from purple bacteria (6), from PSII (7), and cytochrome c oxidase (8). After pulsed illu...

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“…They showed that, on the contrary, the relative amplitudes of the fast and slow phases were independent of the membrane potential. Leibl and co-workers (13,48) have also concluded from photovoltage measurements that the rate of electron transfer from F X Ϫ to F A /F B ( Յ50 ns) is faster than that of the slow phase of A 1 Ϫ oxidation. Both of these experimental observations thus argue against the equilibrium model and in favor of one where either the two quinones operate independently in a two-pathway model or where only one of the quinones is functional, but where there is a heterogeneity in the centers giving rise to two different rate constants for A 1 Ϫ to F X electron transfer (12).…”

Section: Resultsmentioning

confidence: 99%

Biochemical and Biophysical Characterization of Photosystem I from Phytoene Desaturase and ζ-Carotene Desaturase Deletion Mutants of Synechocystis Sp. PCC 6803

Bautista

Rappaport

Guergova-Kuras

et al. 2005

Journal of Biological Chemistry

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In photosystem I, oxidation of reduced acceptor A 1 ؊ through iron-sulfur cluster F X is biphasic with halftimes of ϳ5-30 ns ("fast" phase) and ϳ150 -300 ns ("slow" phase). Whether these biphasic kinetics reflect unidirectional electron transfer, involving only the PsaA-side phylloquinone or bi-directional electron transfer, involving both the PsaA-and PsaB-side phylloquinones, has been the source of some controversy. Brettel ؊ difference spectra, measured in cells and photosystem I complexes, retain the electrochromic band shift centered at 450 nm but show a complete loss of the electrochromic band shifts centered at 500 -510 nm. Thus, the latter clearly arise from ␤-carotene. In the wild type, the electrochromic band shift of the slow phase (centered at 500 nm) is shifted by 6 nm to the blue compared with the fast phase (centered at 506 nm). Thus, the carotenoid pigments acting as electrochromic markers during the fast and slow phases of A 1 ؊ oxidation are different, indicating the involvement of both the PsaA-and the PsaB-side phylloquinones in photosystem I electron transport.

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Primary Charge Separation in Photosystem I: A Two-Step Electrogenic Charge Separation Connected with P700+A0- and P700+A1- Formation

Cited by 75 publications

References 46 publications

Competition between annihilation and trapping leads to strongly reduced yields of photochemistry under ps-flash excitation

Competition between annihilation and trapping leads to strongly reduced yields of photochemistry under ps-flash excitation

Electrogenic light reactions in photosystem I: resolution of electron-transfer rates between the iron-sulfur centers.

Biochemical and Biophysical Characterization of Photosystem I from Phytoene Desaturase and ζ-Carotene Desaturase Deletion Mutants of Synechocystis Sp. PCC 6803

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