Current Questions on Optical Properties and Energy Transfer in the Reaction Center of Photosystem II

Gorkom, Hans J. van

doi:10.1007/978-94-009-0173-5_100

Cited by 5 publications

(2 citation statements)

References 35 publications

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“…It should also be noted that our observation of the anisotropy decays on a sub-picosecond time scale provides further evidence that the 21 ps charge separation component proceeds from a core of equilibrated reaction center excited states. This component is therefore not limited by a slow energy transfer step, contrary to a recent suggestion …”

Section: Discussioncontrasting

confidence: 99%

Sub-picosecond Equilibration of Excitation Energy in Isolated Photosystem II Reaction Centers Revisited: Time-Dependent Anisotropy

et al. 1996

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Transient absorption spectroscopy has been used to study sub-picosecond energy transfer processes in isolated photosystem II (PS II) reaction centers. As reported previously [Durrant, J. R.; et al. Proc. Natl. Acad. Sci. U.S.A. 1992 , 89, 11632−11636], using long wavelength (694 nm) excitation, spectral evolution of the isotropic Q y band bleach/stimulated emission is dominated by energy transfer processes with a 100 ± 50 fs time constant. In contrast, depolarization of this signal occurs with a time constant of 400 ± 30 fs, from an initial anisotropy of ∼0.4 to a value of ∼0.15 at 1.5 ps. This decay of the anisotropy is attributed to energy transfer between at least two degenerate states contributing to reaction center absorption circa 680 nm, with these states having approximately orthogonal transition dipoles. The transient anisotropy barely changes between 1.5 and 60 ps, indicating that under these excitation conditions equilibration of the excitation energy between reaction center excited states occurs on a sub-picosecond time scale. Transient data collected for pheophytin Q x absorption bands indicate that pheophytin molecules are included in the 100 fs equilibration process. These results are discussed in the context of the PS II multimer model and are shown to be in good agreement with this model.

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Section: Discussioncontrasting

confidence: 99%

Sub-picosecond Equilibration of Excitation Energy in Isolated Photosystem II Reaction Centers Revisited: Time-Dependent Anisotropy

et al. 1996

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“…The question of the purity of the PS II RC complex has recently been a matter of considerable debate and so has its pigment composition (Seibert, 1993;van Gorkom, 1995). It has been suggested from spectroscopic (Chang et al, 1994a) and immunological studies (Pueyo et al, 1995) that wellpurified PS II RC complexes bind four Chl a, two Pheo a, and one -Car molecules and that higher Chl contents arise from contamination with the core antenna complex CP47.…”

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Purification and Spectroscopic Characterization of Photosystem II Reaction Center Complexes Isolated with or without Triton X-100

et al. 1996

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The pigment composition of the isolated photosystem II reaction center complex in its most stable and pure form currently is a matter of considerable debate. In this contribution, we present a new method based on a combination of gel filtration chromatography and diode array detection to analyze the composition of photosystem II reaction center preparations. We show that the method is very sensitive for the detection of contaminants such as the core antenna protein CP47, pigment-free and denatured reaction center proteins, and unbound chlorophyll and pheophytin molecules. We also present a method by which the photosystem II reaction center complex is highly purified without using Triton X-100, and we show that in this preparation the contamination with CP47 is less than 0.1%. The results strongly indicate that the photosystem II reaction center complex in its most stable and pure form binds six chlorophyll a, two pheophytin a, and two -carotene molecules and that the main effect of Triton X-100 is the extraction of -carotene from the complex. Analysis of 4 K absorption and emission spectra indicates that the spectroscopic properties of this preparation are similar to those obtained by a short Triton X-100 treatment. In contrast, preparations obtained by long Triton X-100 treatment show decreased absorption of the shoulder at 684 nm in the 4 K absorption spectrum and an increased number of pigments that trap excitation energy at very low temperatures. We conclude that the 684 nm shoulder in the 4 K absorption spectrum should at least in part be attributed to the primary electron donor of photosystem II.

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Evidence for delocalization of the triplet state ³P₆₈₀ in the D₁D₂cytb₅₅₉‐complex of photosystem II

Kamlowski

Frankemöller

Est

et al. 1996

Ber Bunsenges Phys Chem

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Spin polarized transient ESR spectra of 3P68, in D,D2cytb,59-complexes of Photosystem 11 are studied as a function of temperature. The spin polarization as well as the rise time of the ESR signals are characteristic of triplet formation via recombination from the primary radical pair P&Pheo-Below 100 K the well-known spectrum of 3P6,0 is observed with zero-field splitting (zfs) parameters associated with the triplet state of monomeric chlorophyll-a (Chl). Between 100 K and 200 K the spectral pattern changes drastically and above 200 K a considerably narrowed triplet spectrum (i.e. reduced zfs parameters) is observed which suggests a delocalization of the triplet excitation. When the temperature-dependent spectra are normalized to the same triplet yield, isosbestic points are observed indicating that the spectra are weighted sums of the limiting case spectra at low and high temperature (10 K and 250 K, respectively). This is taken as evidence that a transition between two triplet states of different electronic origin occurs. The coefficients of this superposition follow a sigmoidal temperature dependence which suggests a distribution of activation energies for the triplet delocalization process in accordance with a glass-like distribution of protein matrix conformations. The narrowing of the spectrum at high temperature can be interpreted as thermally activated delocalization of the triplet excitation over at least two Chl units with different orientations with respect to the PS I1 reaction center, viz. one oriented with its plane tilted 30" with respect to the membrane plane and the other with its plane perpendicular. The similarities and differences in the cofactor arrangement of PS I1 and purple bacteria reaction center are discussed.

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Current Questions on Optical Properties and Energy Transfer in the Reaction Center of Photosystem II

Cited by 5 publications

References 35 publications

Sub-picosecond Equilibration of Excitation Energy in Isolated Photosystem II Reaction Centers Revisited: Time-Dependent Anisotropy

Sub-picosecond Equilibration of Excitation Energy in Isolated Photosystem II Reaction Centers Revisited: Time-Dependent Anisotropy

Purification and Spectroscopic Characterization of Photosystem II Reaction Center Complexes Isolated with or without Triton X-100

Evidence for delocalization of the triplet state ³P₆₈₀ in the D₁D₂cytb₅₅₉‐complex of photosystem II

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Current Questions on Optical Properties and Energy Transfer in the Reaction Center of Photosystem II

Cited by 5 publications

References 35 publications

Sub-picosecond Equilibration of Excitation Energy in Isolated Photosystem II Reaction Centers Revisited: Time-Dependent Anisotropy

Sub-picosecond Equilibration of Excitation Energy in Isolated Photosystem II Reaction Centers Revisited: Time-Dependent Anisotropy

Purification and Spectroscopic Characterization of Photosystem II Reaction Center Complexes Isolated with or without Triton X-100

Evidence for delocalization of the triplet state 3P680 in the D1D2cytb559‐complex of photosystem II

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Evidence for delocalization of the triplet state ³P₆₈₀ in the D₁D₂cytb₅₅₉‐complex of photosystem II