Optical difference spectrum of the electron acceptor A<sub>o</sub>in photosystem I

Mansfield, Royston W.; Evans, M.C.W.

doi:10.1016/0014-5793(85)81291-6

Cited by 57 publications

(13 citation statements)

References 18 publications

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“…This chlorophyll molecule is thought to have an absorption peak centred at 670 nm (Mansfield and Evans 1985) and would be clearly distinguishable from P700 in Fig. 2. The absence of such a signal in our data suggests a more complex action of A0 than simply a "metastable" electron acceptor.…”

Section: Discussionmentioning

confidence: 99%

Energy transfer to low energy chlorophyll species prior to trapping by P700 and subsequent electron transfer

et al. 1989

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It is found that the two singlet state lifetimes observed in medium sized isolated Photosystem One reaction centres belong to two distinct sets of particles. The nanosecond lifetime is due to PS1 particles in which P700 does not trap excitation energy, and the excitation energy is homogeneously distributed within the antennae of these particles. The spectral features of the picosecond component show that excitation energy in the antenna has become largely concentrated in one or more low energy (red) chlorophyll species within 3.5 ps. Antennae which have become decoupled from P700 also appear to be decoupled from these red "ancillary" chlorophylls, and this suggests that some substructure or level of organisation links them to P700.The rate of quenching of antenna singlet states appears to be independent of the redox state of P700 under the conditions used here, and oxidising P700 does not prevent excitation energy from reaching the red chlorophyll species in the antenna.We find no evidence in the data presented here of a chlorophyll molecule acting as a "metastable" primary acceptor (A0). The lower limit for the detection of such a species in these data is 20% of the optical density of the transient P700 bleach.

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Section: Discussionmentioning

confidence: 99%

Energy transfer to low energy chlorophyll species prior to trapping by P700 and subsequent electron transfer

et al. 1989

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“…Thus because the quadrilateral de®ned by the centroids of eC 2 , eC H 2 , eC 3 and eC H 3 is roughly coplanar with the C 2 (AB) axis (Figure 8(c)), each of eC 3 and eC H 3 is largely equidistant to both eC 1 and eC H 1 . On account of their position, approximately half-way between P700 and F X , and by analogy to the position of bacteriopheophytins in PbRC, at least one of them is assumed to be equivalent to the spectroscopically characterized primary acceptor, A 0 , proposed to be a Chla monomer (Mans®eld & Evans, 1985;Brettel, 1997).…”

Section: Primary Electron Acceptormentioning

confidence: 99%

Photosystem I of Synechococcus elongatus at 4 Å resolution: comprehensive structure analysis

Schubert

Klukas

Krauß

et al. 1997

Journal of Molecular Biology

274

295

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“…However, the results of flash absorption measurements on the recombination of P~00A? Recently, using photo-accumulation techniques, Mansfield and Evans (1985) poised PSI particles in the states P700m0A~ -and P700m0-A~-and determined the absorption difference spectra of A~/Ai-and A0/A0-• It was found that there were no absorption changes in the range of 350-750 nm due to the reduction of A~. Moreover, using Q-band EPR (35 GHz microwave frequency) evidence was found for substantial g-anisotropy in the EPR spectrum of A1, which conflicts with the idea that A~ is a chlorophyll-like molecule (Thurnauer and Gast 1985).…”

Section: Introductionmentioning

confidence: 99%

Comparison of the electron spin polarized spectrum found in plant photosystem I and in iron-depleted bacterial reaction centers with time-resolved K-band EPR; evidence that the photosystem I acceptor A1 is a quinone

et al. 1987

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The suggestion that the electron acceptor A1 in plant photosystem I (PSI) is a quinone molecule is tested by comparisons with the bacterial photosystem. The electron spin polarized (ESP) EPR signal due to the oxidized donor and reduced quinone acceptor (P 870 (+) Q(-)) in iron-depleted bacterial reaction centers has similar spectral characteristics as the ESP EPR signal in PSI which is believed to be due to P 700 (+) A 1 (-) , the oxidized PSI donor and reduced A1. This is also true for better resolved spectra obtained at K-band (∼24 GHz). These same spectral characteristics can be simulated using a powder spectrum based on the known g-anisotropy of reduced quinones and with the same parameter set for Q(-) and A1 (-). The best resolution of the ESP EPR signal has been obtained for deuterated PSI particles at K-band. Simulation of the A1 (-) contribution based on g-anisotropy yields the same parameters as for bacterial Q(-) (except for an overall shift in the anisotropic g-factors, which have previously been determined for Q(-)). These results provide evidence that A1 is a quinone molecule. The electron spin polarized signal of P700 (+) is part of the better resolved spectrum from the deuterated PSI particles. The nature of the P700 (+) ESP is not clear; however, it appears that it does not exhibit the polarization pattern required by mechanisms which have been used so far to explain the ESP in PSI.

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Optical difference spectrum of the electron acceptor A_oin photosystem I

Abstract: Photosystem I Primary acceptor Optical difference spectrum Chlorophyll a monomer

Cited by 57 publications

References 18 publications

Energy transfer to low energy chlorophyll species prior to trapping by P700 and subsequent electron transfer

Energy transfer to low energy chlorophyll species prior to trapping by P700 and subsequent electron transfer

Photosystem I of Synechococcus elongatus at 4 Å resolution: comprehensive structure analysis

Comparison of the electron spin polarized spectrum found in plant photosystem I and in iron-depleted bacterial reaction centers with time-resolved K-band EPR; evidence that the photosystem I acceptor A1 is a quinone

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Optical difference spectrum of the electron acceptor Aoin photosystem I

Abstract: Photosystem I Primary acceptor Optical difference spectrum Chlorophyll a monomer

Cited by 57 publications

References 18 publications

Energy transfer to low energy chlorophyll species prior to trapping by P700 and subsequent electron transfer

Energy transfer to low energy chlorophyll species prior to trapping by P700 and subsequent electron transfer

Photosystem I of Synechococcus elongatus at 4 Å resolution: comprehensive structure analysis

Comparison of the electron spin polarized spectrum found in plant photosystem I and in iron-depleted bacterial reaction centers with time-resolved K-band EPR; evidence that the photosystem I acceptor A1 is a quinone

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Optical difference spectrum of the electron acceptor A_oin photosystem I