Determination of P680 singlet state lifetimes in photosystem two reaction centres

Durrant, James R.; Hastings, Gary; Hong, Qiang; Barber, James; Porter, George; Klug, David R.

doi:10.1016/0009-2614(92)85088-r

Cited by 43 publications

(64 citation statements)

References 23 publications

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“…In TIME ps 0.010 described in our earlier report was carried out at the magic angle (24). In the work of Durrant et al (33,35,36) The data in Fig. 2 addition, selective excitation of a subset of the pigments in this wavelength region when the RCs are excited at present in the PSII RC is complicated by the spectral width of wavelengths shorter than 680 nm for the parallel polarization.…”

Section: Discussionmentioning

confidence: 99%

“…The 20-to 25-ps energy transfer process was also observed in fluorescence decay measurements using the original Nanba and Satoh preparation (28,29). Recent fluorescence data from Roelofs et al (30) at both 277 K and 77 K on RCs with 4-5 Chl molecules and from Gatzen et al (31) Using PSII RCs with 6 Chl molecules, Durrant et al (33) and Hastings et al (34) have obtained transient absorption data that have led them to propose that the formation time for P680+-Pheo-is 21 ps. These conclusions are based primarily on observation of the appearance of the Pheo bleach at 545 nm.…”

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confidence: 89%

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Femtosecond photodichroism studies of isolated photosystem II reaction centers.

Wiederrecht

Seibert

Govindjee

et al. 1994

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

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Photosynthetic conversion oflight energy into chemical potential begins in reaction center protein complexes, where rapid charge separation occurs with nearly unit quantum efficiency. Primary charge separation was studied in isolated photosystem H reaction centers from spinach containing 6 chlorophyll a, 2 pheophytin a (Pheo), 1 cytochrome b559, and 2 f-carotene molecules. Time-resolved pump-probe kinetic spectroscopy was carried out with 105-fs time resolution and with the pump laser polarized parallel, perpendicular, and at the magic angle (54.70) relative to the polarized probe beam. The time evolution of the transient absorption changes due to the formation of the oxidized primary electron donor P680+ and the reduced primary electron acceptor Pheo-were measured at 820 nm and 545 nm, respectively. In addition, kinetics were obtained at 680 nm, the wavelength ascribed to the Q transition of the primary electron donor P680 in the reaction center. At each measured probe wavelength the kinetics of the transient absorption changes can be fit to two major kinetic components. The relative amplitudes of these components are strongly dependent on the polarization of the pump beam relative to that of the probe. At the magic angle, where no photoselection occurs, the amplitude of the 3-ps component, which is indicative of the charge separation, dominates. When the primary electron acceptor Pheo is reduced prior to P680 excitation, the 3-ps component is eliminated.The detailed mechanism of primary charge separation in isolated reaction center (RC) complexes from photosynthetic organisms is an important topic of current interest (1-4). Femtosecond transient absorption spectroscopy has been used to probe a variety of issues regarding primary charge separation in the RCs of anoxygenic bacteria. It is of considerable interest to obtain the analogous data for photosystem II (PSII) from algae and higher plants because of the similarities between the bacterial and PSII RCs (5, 6). The first reported isolation of the PSII RC, the D1-D2-cytochrome b559 (cyt-b559) protein complex, from higher plants by Nanba and Satoh (5) yielded a complex containing 4-5 chlorophyll a (Chl) molecules (6-8). Subsequent work (9, 10) demonstrated that the RC complex, as originally isolated, was quite unstable, and thus of limited use in many spectroscopic studies. Fortunately, simple modifications to the Nanba and Satoh procedure, such as substituting the detergent dodecyl P-maltoside (DM) for Triton X-100 (9) and adding an active enzymatic 02-scrubbing system in situ (10), improve the stability of the PSII RC under prolonged illumination. The use of DM does not alter the spectroscopic properties of the RC as does Triton X-100 (11-13). Other changes in the isolation procedure have led to stable RCs that contain 6 Chl, 2 pheophytin a (Pheo), 1 cyt-b559, and 2 3-carotene molecules per RC (14-17).Carrying out detailed spectroscopic studies of PSII RCs is difficult because at room temperature the Q bands of all the chlorophylls and pheophytins wi...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 89%

Femtosecond photodichroism studies of isolated photosystem II reaction centers.

Wiederrecht

Seibert

Govindjee

et al. 1994

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

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“…In particular, Small et al (28,32) (4). We also reported the observation of two faster kinetic components with lifetimes of 400 fs and 3.5 ps after direct excitation of P680 (33). These components were both assigned to decay of an initially delocalized P680 singlet excited state, although it was not possible to determine whether these decays resulted from energy-or electron-transfer processes.…”

mentioning

confidence: 93%

Subpicosecond equilibration of excitation energy in isolated photosystem II reaction centers.

Durrant

Hastings

Joseph

et al. 1992

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

103

128

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PhotosystemIH reaction centers have been studied by femtoend trent absorption spectroseopy. We demonstrate that it is possible to achieve good photoselectivity between the primary electron donor P680 and the majority of the accessory chlorins. Energy tanser can be observed in both directions between P680 and these accessory chlorins depending on which Is initily excited. This oxidizing potential is used to drive water splitting, which gives rise to oxygen evolution. The primary electron donor of PSII is thought to correspond to a spectral feature at 680 nm and is referred to as P680 (3), while a pheophytin (Ph) molecule functions as an electron acceptor (4-6). Studies of PSII core complexes binding 60 and 80 antenna chlorophylls have suggested that the primary radical pair P680+Ph-is formed at a rate of 4100 psfollowing the absorption ofa photon by antenna pigments (7).A similar conclusion was reached from photovoltage studies of larger PSII complexes (8). A kinetic model, in which there is a rapid (--1 ps) equilibration of excitation energy between the antenna pigments and P680, followed by the observed trapping of the excitation energy by radical pair formation in ""100 ps, has been proposed for this process (refs. 9 and 10; reviewed in ref. 2). This so-called trapping limited model (11) is valid when the rate of electron transfer from the primary electron donor is slower than energy transfer back to the antenna pigments. This model has also been applied to other photosynthetic antenna/reaction center complexes (12)(13)(14).However, previous studies have not been able to time resolve the energy-transfer processes that are predicted to cause the equilibration of excitation energy between the antenna and primary electron donor pigments prior to radical pair formation.We report here a study ofexcitation energy equilibration in the isolated Dl/D2/cytochrome b559 complex, which is the reaction center of PSII. This complex is much smaller than the isolated PSII core complexes discussed above, binding only six chlorophyll a and two Ph a pigments (15, 16). While several of these pigments are presumably involved in electron-transfer processes, these pigments will also function in an energy-transferring capacity before charge separation. Time-resolved fluorescence studies have determined that at least 94% of the chlorin pigments in our PSI1 reaction center preparation are able to transfer excitation energy to P680, resulting in a near unity quantum yield of the primary radical pair (17,18). In a previous study, we determined that when P680 is directly excited, Ph reduction occurs primarily at a rate of 21 ps-1 in isolated PSII reaction centers at room temperature (4).There have been several discussions of the similarities between the PSII reaction center of higher plants and the reaction center of purple bacteria (19,20). However, these two complexes are likely to be very different in terms oftheir energy-transfer kinetics when isolated from their antenna systems. The lowest SO-S, opticil transition for the pr...

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“…Near room temperature, the RC kinetics have been studied by both time resolved Chl a fluorescence [22][23][24] and transient absorption techniques [15][16][17][18][25][26][27][28][29][30][31][32][33]. While the time-resolved fluorescence measurements are hindered by the presence of processes occurring faster than the time resolution of the instrument, the transient absorption measurements are hampered by the lack of unambiguous indicators differentiating excitation energy transfer from charge separation.…”

Section: Introductionmentioning

confidence: 99%

“…Much of the work has been done probing the composite Q>. band itself [15][16][17][25][26][27][28][31][32][33][34]. Because of the spectral congestion of the six Chl a and two Pheo a pigments in this band, it is difficult to use bleaching as an indicator of ground state depopulation of a specific pigment or group thereof.…”

Section: Introductionmentioning

confidence: 99%

Wavelength and intensity dependent primary photochemistry of isolated Photosystem II reaction centers at 5°C

Greenfield¹,

Seibert²,

Wasielewski³

1996

Chemical Physics

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The long wavelength absorption band of the isolated Photosystem II reaction center was directly excited at five wavelengths between 655 and 689 nm to study the effects of excitation wavelength and intensity on both excitation energy transfer and charge separation processes. Subpicosecond transient absorption measurements were made monitoring principally the bleach of the pheophytin a Qx band at 544 nm. At all pump wavelengths, the kinetics require three exponentials (1-3, 10-25 and 50-100 ps) to be fit properly. The pump energy was varied by a factor of twenty-five (40-1000 nJ), with no apparent effect on either the rates or the amplitude ratios of the three components, although clear evidence of nonlinear behavior was observed at the higher excitation energies. The dependence of both the rates and amplitude ratios of the three components upon pump wavelength will be discussed in terms of excitation energy transfer occurring on a 30 ps timescale. Selective excitation into the short and long-wavelength sides of the composite Qy band give identical transient spectra at 500 ps, indicating near-unity efficiency of excitation energy transfer. At 1 ps, the spectra are quite different, calling into question the extent of ultrafast ( ~ 100 fs) excitation energy transfer. The time after the excitation pulse at which the transient crosses A A = 0 was found to be a highly sensitive measure of both the excitation energy and the identity of the pigment pool that had been excited.

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Determination of P680 singlet state lifetimes in photosystem two reaction centres

Cited by 43 publications

References 23 publications

Femtosecond photodichroism studies of isolated photosystem II reaction centers.

Femtosecond photodichroism studies of isolated photosystem II reaction centers.

Subpicosecond equilibration of excitation energy in isolated photosystem II reaction centers.

Wavelength and intensity dependent primary photochemistry of isolated Photosystem II reaction centers at 5°C

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