Forward electron transfer from phylloquinone A1 to iron-sulfur centers in spinach photosystem I

Sétif, Pièrre; Brettel, Klaus

doi:10.1021/bi00082a002

Cited by 102 publications

(93 citation statements)

References 39 publications

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“…The absorption changes associated with reoxidation of PhQ are described by two exponential decay components (18,19). The fact that point mutations near PhQ A or PhQ B resulted in changes in the rates of either the slower ( Ϸ 200 ns) or faster ( Ϸ 20 ns) components, respectively (3,5), are most easily interpreted in terms of a bidirectional model, in which ET occurs with a given probability in either the A-or B-branch, resulting in reduction of PhQ A or PhQ B , respectively.…”

Section: Resultsmentioning

confidence: 99%

Directing electron transfer within Photosystem I by breaking H-bonds in the cofactor branches

Est

Lucas

et al. 2006

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

101

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Photosystem I has two branches of cofactors down which lightdriven electron transfer (ET) could potentially proceed, each consisting of a pair of chlorophylls (Chls) and a phylloquinone (PhQ). Forward ET from PhQ to the next ET cofactor (F X) is described by two kinetic components with decay times of Ϸ20 and Ϸ200 ns, which have been proposed to represent ET from PhQ B and PhQA, respectively. Immediately preceding each quinone is a Chl (ec3), which receives a H-bond from a nearby tyrosine. To decrease the reduction potential of each of these Chls, and thus modify the relative yield of ET within the targeted branch, this H-bond was removed by conversion of each Tyr to Phe in the green alga Chlamydomonas reinhardtii. Together, transient optical absorption spectroscopy performed in vivo and transient electron paramagnetic resonance data from thylakoid membranes showed that the mutations affect the relative amplitudes, but not the lifetimes, of the two kinetic components representing ET from PhQ to F X. The mutation near ec3 A increases the fraction of the faster component at the expense of the slower component, with the opposite effect seen in the ec3B mutant. We interpret this result as a decrease in the relative use of the targeted branch. This finding suggests that in Photosystem I, unlike type II reaction centers, the relative efficiency of the two branches is extremely sensitive to the energetics of the embedded redox cofactors.Chlamydomonas ͉ directionality ͉ photosynthetic reaction center ͉ pump-probe spectroscopy ͉ transient EPR P hotosynthetic reaction centers (RCs) are the membrane proteins responsible for the capture and storage of light energy in photosynthetic organisms. As with all of the RCs, Photosystem I (PS1) has a C2 symmetrical structure with two virtually identical branches of redox cofactors extending across the membrane (see Fig. 1). The x-ray crystal structure of PS1 from Thermosynechococcus elongatus (1) has allowed identification of amino acid residues interacting with the electron transfer (ET) cofactors, permitting the use of site-directed mutagenesis to investigate to what extent ET occurs in the two branches. Many of these studies (2-10) point toward the possibility that ET takes place in both branches of cofactors (A-branch and Bbranch; see Fig. 1). The data consistently show that the major fraction occurs in the A-branch and that the slow phase of ET from phylloquinone (PhQ) to F x is associated with this branch. The involvement of the B-branch is less clear, but there is mounting evidence to support the assignment of the fast component of PhQ to F x ET to this branch. If ET does indeed occur in both branches in PS1, this behavior would be remarkably different from the type II RCs. In purple bacterial RCs, for example, it is well known that initial ET is biased almost exclusively toward the A-branch, probably because the B-branch quinone is a mobile electron and proton carrier in this type of RC. The strong biasing of the ET in the type II RCs makes it difficult to investigate the fac...

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Section: Resultsmentioning

confidence: 99%

Directing electron transfer within Photosystem I by breaking H-bonds in the cofactor branches

Est

Lucas

et al. 2006

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

101

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“…Remarkably, in PS I from spinach the 150 ns phase disappears, whereas the 25 ns phase is still observed, when both FA and F, are pre-reduced [8]. On the other hand, in PS I core preparations lacking the FNB containing subunit C, the state P700' F, is formed with high quantum yield decaying by charge recombination with a half life of about 1.2 ms [8]. This result does not exclude that F, is located on a side path of electron transfer and functions as an electron acceptor only after depletion of F,,,.…”

Section: Introductionmentioning

confidence: 94%

“…Subsequent charge stabilisation is achieved by electron transfer from A; to the secondary acceptor A, (vitamin K,). For the reoxidation of A; a half life of 200 ns was found in PS I complexes from Synechococcus [7], whereas in PS I from spinach A; decays biphasically with t,,2 = 25 ns and 150 ns and relative amplitudes depending on the preparation [8]. It is widely accepted that the electron from A; is transferred to F,.…”

Section: Introductionmentioning

confidence: 99%

“…The observation, that the 200 ns forward electron transfer from A; to an iron-sulfur-center is blocked in Synechococcus after chemical pre-reduction of both FA and F,, may even indicate that F, is not involved in normal forward electron transfer [lo]. Remarkably, in PS I from spinach the 150 ns phase disappears, whereas the 25 ns phase is still observed, when both FA and F, are pre-reduced [8]. On the other hand, in PS I core preparations lacking the FNB containing subunit C, the state P700' F, is formed with high quantum yield decaying by charge recombination with a half life of about 1.2 ms [8].…”

Section: Introductionmentioning

confidence: 99%

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Spectroscopic characterization of PS I core complexes from thermophilic Synechococcus sp

et al. 1994

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Monomeric and trimeric PS I complexes missing the three stromal subunits E,C and D (termed PS I core complexes) were prepared from the thermophilic cyanobacterium Synechococcus sp. by incubation with urea. The subunits E,C and D are sequentially removed. In the monomeric PS I the subunit C is removed with a half life of approx. 5 min. This is about eight times faster than in the trimeric PS I complex. In parallel with the removal of the FAB containing subunit C the reduction kinetics of P700+ changed from a half life of about 25 ms to about 750 μs. The partner of P700+ in the 750 μs charge recombination was identified to be FX by the difference spectrum of this phase. There are some minor differences in the spectra of trimeric and monomeric PS I core complexes. At 77K the forward electron transfer from A − 1 to FX is blocked in the major fraction of the PS I core complexes and P700+A− 1 recombines with a half life of about 220 μs. In the remaining fraction P700+FX − is formed and decays with a half life of approx. 10 ms at 77 K. The kinetics of the forward electron transfer from A− 1 to the iron‐sulfur‐clusters was measured in the native PS I and the corresponding core complexes. The reoxidation kinetics of A− 1 are identical in both cases (t 12 = 180 ns). We conclude that Fx is an obligatory intermediate in the normal forward electron transfer.

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“…In contrast to PSII where electron transfer (ET) is known to be primarily on a single branch, data from transient EPR implied both branches to be active in PSI [12][13][14]. However, the conservation of the occurrence of bidirectional ET among different species and varying experimental conditions remains under discussion [11].…”

Section: Introductionmentioning

confidence: 99%

15N Photo-CIDNP MAS NMR To Reveal Functional Heterogeneity in Electron Donor of Different Plant Organisms

et al. 2011

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In plants and cyanobacteria, two light-driven electron pumps, photosystems I and II (PSI, PSII), facilitate electron transfer from water to carbon dioxide with quantum efficiency close to unity. While similar in structure and function, the reaction centers of PSI and PSII operate at widely different potentials with PSI being the strongest reducing agent known in living nature. Photochemically induced dynamic nuclear polarization (photo-CIDNP) in magic-angle spinning (MAS) nuclear magnetic resonance (NMR) measurements provides direct excess to the heart of large photosynthetic complexes (A. Diller, Alia, E. Roy, P. Gast, H.J. van Gorkom, J. Zaanen, H.J.M. de Groot, C. Glaubitz, J. Matysik, Photosynth. Res. 84, 303-308, 2005; Alia, E. Roy, P. Gast, H.J. van Gorkom, H.J.M. de Groot, G. Jeschke, J. Matysik, J. Am. Chem. Soc. 126, 12819-12826, 2004). By combining the dramatic signal increase obtained from the solid-state photo-CIDNP effect with 15 N isotope labeling of PSI, we were able to map the electron spin density in the active cofactors of PSI and study primary charge separation at atomic level. We compare data obtained from two different PSI proteins, one from spinach (Spinacia oleracea) and other from the aquatic plant duckweed (Spirodella oligorrhiza). Results demonstrate a large flexibility of the PSI in terms of its electronic architecture while their electronic ground states are strictly conserved.

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Forward electron transfer from phylloquinone A1 to iron-sulfur centers in spinach photosystem I

Cited by 102 publications

References 39 publications

Directing electron transfer within Photosystem I by breaking H-bonds in the cofactor branches

Directing electron transfer within Photosystem I by breaking H-bonds in the cofactor branches

Spectroscopic characterization of PS I core complexes from thermophilic Synechococcus sp

15N Photo-CIDNP MAS NMR To Reveal Functional Heterogeneity in Electron Donor of Different Plant Organisms

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