Electron transfer from A−1to an iron‐sulfur center witht= 200 ns at room temperature in photosystem I Characterization by flash absorption spectroscopy

Brettel, Klaus

doi:10.1016/0014-5793(88)80552-0

Cited by 116 publications

(100 citation statements)

References 27 publications

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“…The spectra of the two nanosecond phases were attributed to reoxidation of A 1 Ϫ . As previously observed in cyanobacteria (27) and Chlorella (13), the nanosecond phases displayed positive absorption in the 370-to 400-nm range, characteristic for semiphylloquinone, and contributions from the electrochromic band shifts induced by the presence of a charge on A 1 . The positive band at 480 nm has been attributed to a shift in the absorption spectrum of a carotenoid molecule in the close vicinity of the phylloquinone.…”

Section: Resultssupporting

confidence: 80%

Evidence for two active branches for electron transfer in photosystem I

Guergova-Kuras

Boudreaux

Joliot

et al. 2001

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

327

288

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All photosynthetic reaction centers share a common structural theme. Two related, integral membrane polypeptides sequester electron transfer cofactors into two quasi-symmetrical branches, each of which incorporates a quinone. In type II reaction centers [photosystem (PS) II and proteobacterial reaction centers], electron transfer proceeds down only one of the branches, and the mobile quinone on the other branch is used as a terminal acceptor. PS I uses iron-sulfur clusters as terminal acceptors, and the quinone serves only as an intermediary in electron transfer. Much effort has been devoted to understanding the unidirectionality of electron transport in type II reaction centers, and it was widely thought that PS I would share this feature. We have tested this idea by examining in vivo kinetics of electron transfer from the quinone in mutant PS I reaction centers. This transfer is associated with two kinetic components, and we show that mutation of a residue near the quinone in one branch specifically affects the faster component, while the corresponding mutation in the other branch specifically affects the slower component. We conclude that both electron transfer branches in PS I are active.

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Section: Resultssupporting

confidence: 80%

Evidence for two active branches for electron transfer in photosystem I

Guergova-Kuras

Boudreaux

Joliot

et al. 2001

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

327

288

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“…4 left, circles) agrees well with P700F,,,/P700+F.& difference spectra reported for the same material [7] and for PS I from spinach [24]. spectrum of monomeric PS I (Fig.…”

Section: Electron Transfer In Ps I Core Complexessupporting

confidence: 81%

“…In both samples the initial (at t 2: 5 ns) absorption change due to the formation of P700'A; is fol- lowed by a kinetic phase with a half life of about 180 ns. This phase has been attributed to the electron transfer from A; to an iron-sulfur-center but it was not possible to clarify which of the iron-sulfur-centers accepts the electron, since the spectral properties of the FeS-centers are nearly identical [7]. For quantitative analysis of the kinetics, the relative size of the 180 ns component in both samples has been determined by fitting the data with one exponential plus a constant.…”

Section: Reoxidation Kinetics Of A;mentioning

confidence: 99%

“…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%

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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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“…Recent studies have indicated that the PS I reaction center contains two molecules of phylloquinone (= vitamin K1)/reaction center [8,9], one of which presumably functions as the primary electron acceptor A1 [10][11][12][13][14][15] and mediates electron transfer between the reduced electron acceptor intermediate, chlorophyll a (A~), and Fx the ironsulfur secondary electron acceptor. Some arguments against the function of phylloquinone, however, still remain ~ [16,17] and its binding site has not been well characterized.…”

Section: Introductionmentioning

confidence: 99%

New herbicide‐binding site in the photosynthetic electron‐transport chain

Itoh

Iwaki

1989

FEBS Letters

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The binding of herbicides to the phylloquinone-(primary electron acceptor A1)-binding site in green plant photosystem (PS) I reaction centers is shown. Dissociation constants (Ka) of various herbicides to the phyUoquinone-binding site were estimated by analyzing their competitive inhibition of the reconstitution of the phylloquinone analogue, menadione (vitamin Ka) , to the phylloquinone-extracted spinach PSI particles. The phyUoquinone-binding site was found to bind o-phenanthroline (Kd= 1.2 x 10 -4 M), but only weak binding was observed with atrazine (Kd> 10 -a M), although both are known to bind specifically to the quinone-(QB)-binding site in reaction centers of purple photosynthetic bacteria or PS II. The inhibitors of the cytochrome b/cl(f) complex, myxothiazol (Ka = 9.5 x l0 -~ M) or antimycin A (Kd = 2.8 x 10 -~ M), also strongly bound to the phylloquinone site. This is the first report showing that the PSI reaction center complex also has a herbicide-binding site, although the site is probably not sensitive in vivo to these herbicides due to its higher affinity for phylloquinone than herbicides. The inhibitor specificity of the PSI phylloquinone site is different from that of the other quinone-functioning sites in the photosynthetic or respiratory electron-transfer chain, suggesting it to have a unique structure.

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Electron transfer from A⁻₁to an iron‐sulfur center witht_{= 200 ns at room temperature in photosystem I Characterization by flash absorption spectroscopy}

Cited by 116 publications

References 27 publications

Evidence for two active branches for electron transfer in photosystem I

Evidence for two active branches for electron transfer in photosystem I

Spectroscopic characterization of PS I core complexes from thermophilic Synechococcus sp

New herbicide‐binding site in the photosynthetic electron‐transport chain

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