Energy transfer, charge separation and pigment arrangement in the reaction center of Photosystem II

Schelvis, Johannes P. M.; Noort, Paula I. van; Aartsma, Thijs J.; Gorkom, Hans J. van

doi:10.1016/0005-2728(94)90229-1

Cited by 120 publications

(130 citation statements)

References 39 publications

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“…The difference in the absorbance spectra of P A and B A poses a fundamental question as to the location and mechanism of primary charge separation in PSII reaction centers. The similarity of the P + Q A --PQ A difference spectrum observed here at 80 K in Synechocystis to that observed at both 5 K (30) and 77 K (54) in Synechococcus indicates that the absorbance spectra of P A and B A are practically invariant between 5 and 80 K and that P + is stabilized on P A at all temperatures including at 5 K. Given the difference in the energies of the lowest excited singlet states (31 meV), the localization of singlet excitation on B A (684 nm) over P A (672.5 nm) is favored by a factor of ∼10 31 at 5 K. As the rate of charge separation is slower (0.4-21 ps) (29,(100)(101)(102) than the rate at which energy is equilibrated within the central pigments of the reaction center (100-250 fs) (103,104), the excited state that drives charge separation must be on B A rather than on P A at low temperature ( Figure 9A,B). This situation is different from what is observed in wild-type bacterial reaction centers where the strong coupling between the P A and P B FIGURE 9: (A) Scheme indicating the various fates of the reaction center following center excitation at 5 and 298 K. The initiators of primary charge separation are B A * at 5 K and B A *, P A * and possibly Ph A * at 298 K. 3 P is stabilized on B A at 5 K but is delocalized at 298 K. P + is stabilized primarily on P A at all temperatures.…”

Section: Location Of 3 P As a Function Of Temperaturementioning

confidence: 99%

“…These authors have speculated that multiple routes for charge separation might exist as well in PSII owing to the much weaker exciton interaction between the reaction center pigments and the absence of a low-energy exciton band of P as a longwavelength trap (33,35). With extrapolation from the bacterial reaction centers, these multiple routes have been proposed by Dekker and van Grondelle (33) as possible sources of the heterogeneity in the kinetics of charge separation that has been observed in PSII (29,(100)(101)(102). Because of the localization of the triplet and the oxidized donor on P in the bacterial reaction centers and the inclined orientation of the reaction center triplet in PSII, Rutherford and co-workers (34,109) have speculated that the monomeric accessory B A chlorophyll might be all or part of P680.…”

Section: Location Of 3 P As a Function Of Temperaturementioning

confidence: 99%

See 1 more Smart Citation

Site-Directed Mutations at D1-His198 and D2-His197 of Photosystem II in Synechocystis PCC 6803: Sites of Primary Charge Separation and Cation and Triplet Stabilization

et al. 2001

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Site-directed mutations were introduced to replace D1-His198 and D2-His197 of the D1 and D2 polypeptides, respectively, of the photosystem II (PSII) reaction center of Synechocystis PCC 6803. These residues coordinate chlorophylls P A and P B which are homologous to the special pair Bchlorophylls of the bacterial reaction centers that are coordinated respectively by histidines L-173 and M-200 (202). P A and P B together serve as the primary electron donor, P, in purple bacterial reaction centers. In PS II, the site-directed mutations at D1 His198 affect the P + -P-absorbance difference spectrum. The bleaching maximum in the Soret region (in WT at 433 nm) is blue-shifted by as much as 3 nm. In the D1 His198Gln mutant, a similar displacement to the blue is observed for the bleaching maximum in the Q y region (672.5 nm in WT at 80 K), whereas features attributed to a band shift centered at 681 nm are not altered. In the Y Z •-Y Z -difference spectrum, the band shift of a reaction center chlorophyll centered in WT at 433-434 nm is shifted by 2-3 nm to the blue in the D1-His198Gln mutant. The D1-His198Gln mutation has little effect on the optical difference spectrum, 3 P-1 P, of the reaction center triplet formed by P + Pheo -charge recombination (bleaching at 681-684 nm), measured at 5-80 K, but becomes visible as a pronounced shoulder at 669 nm at temperatures g150 K. Measurements of the kinetics of oxidized donor-Q A -charge recombination and of the reduction of P + by redox active tyrosine, Y Z , indicate that the reduction potential of the redox couple P + /P can be appreciably modulated both positively and negatively by ligand replacement at D1-198 but somewhat less so at D2-197. On the basis of these observations and others in the literature, we propose that the monomeric accessory chlorophyll, B A , is a long-wavelength trap located at 684 nm at 5 K. B A * initiates primary charge separation at low temperature, a function that is increasingly shared with P A * in an activated process as the temperature rises. Charge separation from B A * would be potentially very fast and form P A + B A -and/or B A + Pheo -as observed in bacterial reaction centers upon direct excitation of B A ) Proc. Natl. Acad Sci. 96, 2054-2059. The cation, generated upon primary charge separation in PSII, is stabilized at all temperatures primarily on P A , the absorbance spectrum of which is displaced to the blue by the mutations. In WT, the cation is proposed to be shared to a minor extent (∼20%) with P B , the contribution of which can be modulated up or down by mutation. The band shift at 681 nm, observed in the P + -P difference spectrum, is attributed to an electrochromic effect of P A + on neighboring B A . Because of its low-energy singlet and therefore triplet state, the reaction center triplet state is stabilized on B A at e80 K but can be shared with P A at >80 K in a thermally activated process.

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Section: Location Of 3 P As a Function Of Temperaturementioning

confidence: 99%

Section: Location Of 3 P As a Function Of Temperaturementioning

confidence: 99%

Site-Directed Mutations at D1-His198 and D2-His197 of Photosystem II in Synechocystis PCC 6803: Sites of Primary Charge Separation and Cation and Triplet Stabilization

et al. 2001

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“…Excitation energy transfer links the pigments on the blue side of the composite Qy band (the "blue" pool) with the active redox pair on the red side of this absorption band (the "red" pool). It has been suggested that the "blue" pool itself is divided into two groups, one of which undergoes rapid (subpicosecond) excitation energy transfer to the "red" pool [15], and the other, weakly coupled to P680, undergoing excitation energy transfer on a tens of picoseconds timescale [16][17][18]. Only at low temperatures are the two main pools directly observable as separate peaks [9].…”

Section: Introductionmentioning

confidence: 99%

“…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%

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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“…A straightforward interpretation of the results from pump-probe measurements in terms of pigment to pigment energy transfer and charge separation rates has proven difficult, mainly due to the congested absorption spectrum of the PSII RC. At room temperature (RT), most groups observed kinetics with lifetimes of 1-3 ps, 10-20 ps and Ͼ1 ns (14)(15)(16)(17)(18)(19)(20) as well as 100-600 fs (21)(22)(23)(24)(25)(26)(27). At very low temperature (4 K) the lifetime of singlet-excited P680 (P680*) was estimated to be 1.9 ps by transient hole-burning spectroscopy (28).…”

mentioning

confidence: 99%

Charge separation in the reaction center of photosystem II studied as a function of temperature

Groot

Mourik

Eijckelhoff

et al. 1997

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

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In photosystem II of green plants the key photosynthetic reaction consists of the transfer of an electron from the primary donor called P680 to a nearby pheophytin molecule. We analyzed the temperature dependence of this reaction by subpicosecond transient absorption spectroscopy over the temperature range 20-240 K using isolated photosystem II reaction centers from spinach. After excitation in the red edge of the Q y absorption band, the decay of the excited state can conveniently be described by two kinetic components that both accelerate with temperature. This temperature behavior differs remarkably from that observed in purple bacterial reaction centers. We attribute the first component, which accelerates from 2.6 ps at 20 K to 0.4 ps at 240 K, to charge separation after direct excitation of P680, and explain its temperature dependence by an intermediate that lies in energy above the singlet-excited P680 and that possibly has charge-transfer character. The second component accelerates from 120 ps at 20 K to 18 ps at 240 K and is attributed to charge separation after direct excitation of the ''trap'' state near-degenerate with P680 and subsequent slow energy transfer from this trap state to P680. We suggest that the slow energy transfer from the trap state to P680 plays an important role in the kinetics of radical pair formation at room temperature.The photochemical reaction center (RC) of photosystem II (PSII) (the D1-D2 cyt.b559 complex) is the smallest unit in PSII that shows photochemical activity. The RC contains six chlorophyll (Chl) a and two pheophytin (Pheo) a molecules (1-4) that all have their lowest electronic transition around 675 nm, as well as two ␤-carotenes. The D1 and D2 polypeptides are homologous to the L and M subunits of bacterial RCs, suggesting an arrangement of the core pigments in the RC of PSII similar to that in the bacterial RC (5). The two additional Chl molecules are probably located near the periphery of the D1-D2 complex.The characterization of energy transfer and charge separation in the PSII RC is less well established than is the case for the bacterial RC (for a review, see ref. 6). This may be due to the fact that the first PSII RC was isolated only in 1987 (7) and that there is no structure available. However, the excited state kinetics of the PSII RC are also inherently more complicated than those of bacterial RCs. The primary electron donor in PSII, called P680, is isoenergetic with some of the other pigments in the RC (8-13) and as a consequence forms only a very shallow trap for excitations.After excitation of P680 an electron is transferred to the photoactive Pheo molecule (6). In isolated PSII RC preparations, further electron transport cannot occur, because the quinone acceptors are lost during the isolation procedure. A straightforward interpretation of the results from pump-probe measurements in terms of pigment to pigment energy transfer and charge separation rates has proven difficult, mainly due to the congested absorption spectrum of the PSII RC. At r...

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Energy transfer, charge separation and pigment arrangement in the reaction center of Photosystem II

Cited by 120 publications

References 39 publications

Site-Directed Mutations at D1-His198 and D2-His197 of Photosystem II in Synechocystis PCC 6803: Sites of Primary Charge Separation and Cation and Triplet Stabilization

Site-Directed Mutations at D1-His198 and D2-His197 of Photosystem II in Synechocystis PCC 6803: Sites of Primary Charge Separation and Cation and Triplet Stabilization

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

Charge separation in the reaction center of photosystem II studied as a function of temperature

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