Temperature Dependence of the Recombination Fluorescence from PS II Core Complexes

Hillmann, B.; Moya, I.; Schlodder, E.

doi:10.1007/978-94-009-0173-5_141

Cited by 3 publications

(2 citation statements)

References 9 publications

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“…Given that the lifetime of the 684 nm Chl Q y state is ∼ 4 ns, 50 one expects that the 684 nm Chl contributes significantly to the fluorescence. On the basis of the results of ref 56, the contribution to the spectrum from P680 delayed fluorescence at 4.2 K due to charge recombination in P680 + Pheo 1 -is expected to be small. It is instructive to use the electron-phonon coupling parameter values (Huang-Rhys factor S and mean phonon frequency ω m ) given in Table 1 to predict the positions of the fluorescence origin bands of P680, Pheo 1 , and the 684 nm Chl.…”

Section: Resultsmentioning

confidence: 97%

Excited States of the 5-Chlorophyll Photosystem II Reaction Center

et al. 1999

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Results of 4.2 K hole burning, chemical reduction (sodium dithionite, in dark and with illumination), and oxidation (ferricyanide) experiments are reported for the isolated PS II reaction center containing five chlorophyll (Chl) molecules (RC-5). Q y states at 679.6 and 668.3 nm are identified as being highly localized on pheophytin a of the D 1 branch (Pheo 1 ) and pheophytin a of the D 2 branch (Pheo 2 ), respectively. The Pheo 1 -Q x and Pheo 2 -Q x transitions were found to lie on the low and high energy sides of the single Pheo-Q x absorption band, at 544.4 and 541.2 nm, respectively. The Q y band of the 684 nm absorbing Chl, which is more apparent in absorption in RC-5 than in RC-6 samples, is assigned to the peripheral Chl on the D 1 side. The results are consistent with that peripheral Chl being Chl z (Stewart, D. H.; Cua, A.; Chisholm, D. A.; Diner, B. A.; Bocian, D. F.; Brudvig, G. W. Biochemistry 1998, 37, 10040). The results indicate that P680, the primary electron donor, is the main acceptor for energy transfer from the Pheo 1 -Q y state and that excitation energy transfer from the Pheo 1 -Q y state and P680* to the 684 nm Chl is inefficient. It is concluded that the procedure used to prepare RC-5 has only a small effect on the energies of the Q y states associated with the core cofactors of the 6-Chl RC as well as the 684 nm Chl. Implications of the results for the multimer model (Durrant, J. R.; Klug, D. R; Kwa, S. L. S.; van Grondelle, R.; Porter, G.; Dekker, J. P. Proc. Natl. Acad. Sci. U.S.A. 1995, 92, 4798) are considered. In that model the Q y -states of the core are significantly delocalized over several cofactors. The results presented provide no support for this model.

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Section: Resultsmentioning

confidence: 97%

Excited States of the 5-Chlorophyll Photosystem II Reaction Center

et al. 1999

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“…The latter were determined from independent experiments and calculations and therefore cannot be adjusted. From measurements of the recombination fluorescence, values for Δ G (0) of 110 meV in D1−D2−cyt b 559 complexes and 170 meV in PS-II core complexes were reported. The latter is very similar to the present estimate and to the Δ G (0) = 170−190 meV determined for the bacterial reaction centers of Rh.…”

Section: Discussionmentioning

confidence: 99%

Light Harvesting in Photosystem II Core Complexes Is Limited by the Transfer to the Trap: Can the Core Complex Turn into a Photoprotective Mode?

2008

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A structure-based modeling and analysis of the primary photophysical reactions in photosystem II (PS-II) core complexes is presented. The modeling is based on a description of stationary and time-resolved optical spectra of the CP43, CP47, and D1-D2-cytb559 subunits and whole core complexes. It shows that the decay of excited states in PS-II core complexes with functional (open) reaction centers (RCs) is limited by the excitation energy transfer from the CP43 and CP47 core antennae to the RC occurring with a time constant of 40-50 ps at room temperature. The chlorophylls responsible for the low energy absorbance bands in the CP43 and CP47 subunits are assigned, and their signatures in hole burning, fluorescence line narrowing, and triplet-minus-singlet spectra are explained. The different locations of these trap states in the CP43 and CP47 antennae with respect to the reaction center lead to a dramatic change of the transfer dynamics at low temperatures. The calculations predict that, compared to room temperature, the fluorescence decay at 77 K should reveal a faster transfer from CP43 and a much slower and highly dispersive transfer from CP47 to the RC. A factor of 3 increase in the fastest decay time constant of fluorescence that was reported to occur when the RC is closed (the plastoquinone QA is reduced) is understood in the present model by assuming that the intrinsic rate constant for primary electron transfer decreases from 100 fs-1 for open RCs to 6 ps-1 for closed RCs, leading to a reduction of the primary electron acceptor PheoD1, in 300 fs and 18 ps, respectively. The model suggests that the reduced QA switches the photosystem into a photoprotective mode in which a large part of the excitation energy of the RC returns to the CP43 and CP47 core antennae, where the physiologically dangerous triplet energy of the chlorophylls can be quenched by the carotenoids. Experiments are suggested to test this hypothesis. The ultrafast primary electron transfer inferred for open RCs provides further support for the accessory chlorophyll ChlD1 to be the primary electron donor in photosystem II.

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