Temperature dependence of biphasic forward electron transfer from the phylloquinone(s) A1 in photosystem I: only the slower phase is activated

Agalarov, Rufat; Brettel, Klaus

doi:10.1016/s0005-2728(03)00024-0

Cited by 84 publications

(96 citation statements)

References 15 publications

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“…Although the focus of this paper was on the reduction of P 700 + by plastocyanin in vivo, we were able to estimate the activation energy of forward ET from PhQ A and PhQ B to be 107-130 meV and 8-47 meV, respectively. These agree reasonably well with the estimates of 65-110 meV and 7-15 meV, obtained in work with purified cyanobacterial PS1 in vitro using a more extensive temperature range (Agalarov and Brettel, 2003).…”

Section: Temperature Dependence Of Et Reactions In Ps1 In Vivosupporting

confidence: 89%

A Combined Genetic, Biochemical, and Biophysical Analysis of the A1 Phylloquinone Binding Site of Photosystem I from Green Algae

Redding¹

2011

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Section: Temperature Dependence Of Et Reactions In Ps1 In Vivosupporting

confidence: 89%

A Combined Genetic, Biochemical, and Biophysical Analysis of the A1 Phylloquinone Binding Site of Photosystem I from Green Algae

Redding¹

2011

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“…However, this is not surprising in light of a recent optical study on PS I from Synechocystis sp. PCC 6803 that showed that the rate of the fast phase was virtually independent of temperature and that its relative amplitude decreased from ϳ28% at room temperature to ϳ20% at 260 K (35). Three other observations at 260 K are surprising, however.…”

Section: Discussionmentioning

confidence: 98%

Electron Transfer in Cyanobacterial Photosystem I

Chitnis

Valieva

et al. 2003

Journal of Biological Chemistry

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102

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The directionality of electron transfer in Photosystem I (PS I) is investigated using site-directed mutations in the phylloquinone (Q K ) and F X binding regions of Synnechocystis sp. PCC 6803. The kinetics of forward electron transfer from the secondary acceptor A 1 (phylloquinone) were measured in mutants using time-resolved optical difference spectroscopy and transient EPR spectroscopy. In whole cells and PS I complexes of the wildtype both techniques reveal a major, slow kinetic component of Ϸ 300 ns while optical data resolve an additional minor kinetic component of Ϸ 10 ns. Whole cells and PS I complexes from the W697F PsaA and S692C PsaA mutants show a significant slowing of the slow kinetic component, whereas the W677F PsaB and S672C PsaB mutants show a less significant slowing of the fast kinetic component. Transient EPR measurements at 260 K show that the slow phase is ϳ3 times slower than at room temperature. Simulations of the early time behavior of the spin polarization pattern of P 700 ؉ A 1 ؊ , in which the decay rate of the pattern is assumed to be negligibly small, reproduce the observed EPR spectra at 260 K during the first 100 ns following laser excitation. Thus any spin polarization from P 700 ؉ F X ؊ in this time window is very weak. From this it is concluded that the relative amplitude of the fast phase is negligible at 260 K or its rate is much less temperature-dependent than that of the slow component. Together, the results demonstrate that the slow kinetic phase results from electron transfer from Q K -A to F X and that this accounts for at least 70% of the electrons. Although the assignment of the fast kinetic phase remains uncertain, it is not strongly temperature dependent and it represents a minor fraction of the electrons being transferred. All of the results point toward asymmetry in electron transfer, and indicate that forward transfer in cyanobacterial PS I is predominantly along the PsaA branch.

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“…Similarly, the observation of a change in the high-field region along with the appearance of a higher frequency shoulder in the dipolar spectrum (this work) may be explained by a partial block in electron transfer through the A-branch due to the change in the ligand to A 0A and the uncovering of the relatively small amount of electron transfer through the B-branch. It remains to be explained how the otherwise fast electron transfer through the B-side cofactors can be observed within the limited EPR time window [20] even at 100 K, given that there is little or no activation energy associated with this electron transfer step [28]. Perhaps, because Asn can potentially form an H-bond to the second C=O of the quinone, the position of the A-branch quinone could have moved in some of the PS I complexes to a position closer to P 700 Á ?…”

Section: Discussionmentioning

confidence: 99%

Alteration of the Axial Met Ligand to Electron Acceptor A0 in Photosystem I: Effect on the Generation of P 700 ·+ A 1 ·− Radical Pairs as Studied by W-band Transient EPR

et al. 2009

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Photosystem I (PS I) mutants from the cyanobacterium Synechocystis sp. PCC 6803 bearing point mutations to the axial ligands of A 0A (M688N PsaA ) and A 0B (M668N PsaB ) were studied by high-field W-band electron paramagnetic resonance (EPR) spectroscopy. It was found that the EPR observables of PS I from the M668N PsaB mutant were virtual identical to that of the wild type (WT), and are clearly distinct from the M688N PsaA mutant. In particular, the P 700 Á ? decay kinetics in the M688N PsaA mutant is significantly slower than in the WT or the M668N PsaB mutant. The analysis of the out-of-phase electron-electron dipolar electron spin echo envelope modulation shows that in the M668N PsaB mutant, the estimated distance of 26.0 ± 0.3 Å agrees well with the 25.8 Å distance for the P 700 Á ? A 1A Á -radical pair measured in the X-ray crystal structure. In the M688N PsaA mutant, two populations are found with estimated distances of 26.0 ± 0.3 and 25.0 ± 0.3 Å in a ratio of 0.7-0.3, which agree well with the 25.8 Å distance for the P 700 Á ? A 1A Á -radical

show abstract

Temperature dependence of biphasic forward electron transfer from the phylloquinone(s) A1 in photosystem I: only the slower phase is activated

Cited by 84 publications

References 15 publications

A Combined Genetic, Biochemical, and Biophysical Analysis of the A1 Phylloquinone Binding Site of Photosystem I from Green Algae

A Combined Genetic, Biochemical, and Biophysical Analysis of the A1 Phylloquinone Binding Site of Photosystem I from Green Algae

Electron Transfer in Cyanobacterial Photosystem I

Alteration of the Axial Met Ligand to Electron Acceptor A0 in Photosystem I: Effect on the Generation of P 700 ·+ A 1 ·− Radical Pairs as Studied by W-band Transient EPR

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