Similarity of primary radical pair recombination in photosystem II and bacterial reaction centers

Völk, Martin; Gilbert, Matthias; Rousseau, Gerhard; Richter, Martin; Ogrodnik, A.; Michel‐Beyerle, M. E.

doi:10.1016/0014-5793(93)80837-k

Cited by 45 publications

(30 citation statements)

References 38 publications

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“…The long-lived component is readily assigned to be mainly due to the radical pair state P680 ϩ Pheo. This state has been reported to have a lifetime of tens of nanoseconds at low temperature (35,36), and its spectrum at 240 K is very similar to that reported earlier at RT by Klug et al (ref. 22 and references therein).…”

Section: Discussionsupporting

confidence: 72%

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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Section: Discussionsupporting

confidence: 72%

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 this case the probability for 3 Chl formation could be very small (18,40). In terms of triplet formation efficiency, one may consider the following series: [P 680 •…”

Section: Discussionmentioning

confidence: 99%

“…•ϩ ͞Pheo •Ϫ may be regenerated in the dark and charge recombination may result in the triplet chlorophyll ( 3 Chl) formation (17,18). Therefore one would expect that charge recombination and hence damage to PSII will occur with increased efficiency per photon absorbed as the rate of excitation decreases.…”

mentioning

confidence: 99%

Mechanism of photosystem II photoinactivation and D1 protein degradation at low light: The role of back electron flow

Keren

Berg

Kan

et al. 1997

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

280

196

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Light intensities that limit electron f low induce rapid degradation of the photosystem II (PSII) reaction center D1 protein. The mechanism of this phenomenon is not known. We propose that at low excitation rates back electron f low and charge recombination between the Q B• Following the discovery of the light dependent turnover of reaction center II (RCII) D1 protein (1), the process of excess light-induced photoinactivation and the related degradation of photosystem II (PSII) proteins (photoinhibition) were studied intensively. Significant progress toward understanding the mechanism(s) involved was achieved (reviewed in refs. [2][3][4]

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“…b The sum of the rate constants for radiative (fluorescence) and non-radiative excited-state decay is assumed to be 1 ns 21 for the here used PSII membrane particles (Leibl et al 1989). c Rate constant for decay of the P680 1 Phe 2 triplet state from (Volk et al 1993). d Population of the P680 1 Phe 2 and excited-antenna state, respectively, relative to the P680 1 Q 2 A population [¼exp(2DG i /k B T)].…”

Section: Quantum Yield Of Individual Recombination Loss Pathwaysmentioning

confidence: 99%

Efficiency and role of loss processes in light‐driven water oxidation by PSII

Grabolle

Dau

2007

Physiologia Plantarum

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Its superior quantum efficiency renders PSII a model for biomimetic systems. However, also in biological water oxidation by PSII, the efficiency is restricted by recombination losses. By laser-flash illumination, the secondary radical pair, P680(+)Q(-) (A) (where P680 is the primary Chl donor in PSII and Q(A), primary quinone acceptor of PSII), was formed in close to 100% of the PSII. Investigation of the quantum efficiency (or yield) of the subsequent steps by time-resolved delayed (10 micros to 60 ms) and prompt (70 micros to 700 ms) Chl fluorescence measurements on PSII membrane particles suggests that (1) the effective rate for P680(+) Q(-) (A) recombination is approximately 5 ms(-1) with an activation energy of approximately 0.34 eV, circumstantially confirming dominating losses by reformation of the primary radical pair followed by ground-state recombination. (2) Because of compensatory influences on recombination and forward reactions, the efficiency is only weakly temperature dependent. (3) Recombination losses are several-fold enhanced at lower pH. (4) Calculation based on delayed-fluorescence data suggests that the losses depend on the state of the water-oxidizing manganese complex, being low in the S(0)-->S(1) and S(1)-->S(2) transition, clearly higher in S(2)-->S(3) and S(3)-->S(4)-->S(0). (5) For the used artificial electron acceptor, the efficiency is limited by acceptor-side processes/S-state decay at high/low photon-absorption rates resulting in optimal efficiency at surprisingly low rates of approximately 0.15-15 photons s(-1) (per PSII). The pH and S-state dependence can be rationalized by the basic model of alternate electron-proton removal proposed elsewhere. A physiological function of the recombination losses could be limitation of the lifetime of the reactive donor-side tyrosine radical (Y(.) (Z)) in the case of low-pH blockage of water oxidation.

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Similarity of primary radical pair recombination in photosystem II and bacterial reaction centers

Cited by 45 publications

References 38 publications

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

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

Mechanism of photosystem II photoinactivation and D1 protein degradation at low light: The role of back electron flow

Efficiency and role of loss processes in light‐driven water oxidation by PSII

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