Thermodynamical and structural information on photosynthetic systems obtained from electroluminescence kinetics

Vos, Marten H.; Gorkom, Hans J. van

doi:10.1016/s0006-3495(90)82499-1

Cited by 38 publications

(19 citation statements)

References 28 publications

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“…The A 1 acceptor is represented by one or two phylloquinone molecules (Q A and Q B ) belonging to the A and B branches of cofactors. The E m value of A 1 was estimated as -800 mV (Vos and Van Gorkom 1990), or at least less than -700 mV (see Brettel and Leibl 2001). The data obtained by Joliot and Joliot (1999) and GuergovaKuras et al (2001) indicated that both quinone molecules participate in the electron transfer to the next electron acceptor-the iron-sulfur cluster F X .…”

Section: Correlation Between the Calculated And Experimental E M Valumentioning

confidence: 96%

“…For example, after the primary charge separation electron resides at the primary acceptor A 0 , it becomes exposed to the electric See for references: a, Brettel and Leibl (2001);b, Shuvalov (1976); c, Kleinherenbrink et al (1994); d, Vos and van Gorkom (1990); e, Iwaki and Itoh (1994); f, Chamorovsky and Cammack (1982); g, Parrett et al (1989); h, Shinkarev et al (2000); I, Golbeck et al (1987); j, Jordan et al (1998); k, Chen et al (2002); l, Stombaugh et al (1976) fields of newly created cation P 700 + and of anions of F X , F A and F B . When the electron is transferred via the chain of carriers, the positive effect of P 700 + decreases, while the negative effect of Fe 4 S 4 clusters increases.…”

Section: Charged Redox Cofactorsmentioning

confidence: 99%

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Semi-continuum electrostatic calculations of redox potentials in photosystem I

et al. 2008

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The midpoint redox potentials (E(m)) of all cofactors in photosystem I from Synechococcus elongatus as well as of the iron-sulfur (Fe(4)S(4)) clusters in two soluble ferredoxins from Azotobacter vinelandii and Clostridium acidiurici were calculated within the framework of a semi-continuum dielectric approach. The widely used treatment of proteins as uniform media with single dielectric permittivity is oversimplified, particularly, because permanent charges are considered both as a source for intraprotein electric field and as a part of dielectric polarizability. Our approach overcomes this inconsistency by using two dielectric constants: optical epsilon(o)=2.5 for permanent charges pre-existing in crystal structure, and static epsilon(s) for newly formed charges. We also take into account a substantial dielectric heterogeneity of photosystem I revealed by photoelectric measurements and a liquid junction potential correction for E(m) values of relevant redox cofactors measured in aprotic solvents. We show that calculations based on a single permittivity have the discrepancy with experimental data larger than 0.7 V, whereas E(m) values calculated within our approach fall in the range of experimental estimates. The electrostatic analysis combined with quantum chemistry calculations shows that (i) the energy decrease upon chlorophyll dimerization is essential for the downhill mode of primary charge separation between the special pair P(700) and the primary acceptor A(0); (ii) the primary donor is apparently P(700) but not a pair of accessory chlorophylls; (iii) the electron transfer from the A branch quinone Q(A) to the iron-sulfur cluster F(X) is most probably downhill, whereas that from the B branch quinone Q(B) to F(X) is essentially downhill.

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Section: Correlation Between the Calculated And Experimental E M Valumentioning

confidence: 96%

Section: Charged Redox Cofactorsmentioning

confidence: 99%

Semi-continuum electrostatic calculations of redox potentials in photosystem I

et al. 2008

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“…Knowledge on the in situ midpoint potential of the quinone occupying the A 1 binding site is a crucial parameter in understanding ET in PSI. The in situ midpoint potential of the A 1A PhQ, found through a variety of indirect approaches undertaken in the past, spans a wide range (-810 --531 mV, see Refs [25,[35][36][37][38][39]), and a consensus value has not yet been reached.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Modeling electron transfer in photosystem I

Makita

Hastings

2016

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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Nanosecond to millisecond time-resolved absorption spectroscopy has been used to study electron transfer processes in photosystem I particles from Synechocystis sp. PCC 6803 with eight different quinones incorporated into the A1 binding site, at both 298 and 77K. A detailed kinetic model was constructed and solved within the context of Marcus electron transfer theory, and it was found that all of the data could be well described only if the in situ midpoint potentials of the quinones fell in a tightly defined range. For photosystem I with phylloquinone incorporated into the A1 binding site all of the time-resolved optical data is best modeled when the in situ midpoint potential of phylloquinone on the A/B branch is -635/-690 mV, respectively. With the midpoint potential of the F(X) iron sulfur cluster set at -680 mV, this indicates that forward electron transfer from A(1)(-) to F(X) is slightly endergonic/exergonic on the A/B branch, respectively. Additionally, for forward electron transfer from A(1)(-) to F(X), on both the A and B branches the reorganization energy is close to 0.7 eV. Reorganization energies of 0.4 or 1.0 eV are not possible. For the eight different quinones incorporated, the same kinetic model was used, allowing us to establish in situ redox potentials for all of the incorporated quinones on both branches. A linear correlation was found between the in situ and in vitro midpoint potentials of the quinones on both branches.

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“…This initially formed radical pair is composed of Chl (43,44), which is further stabilized by the formation of the P ϩ A o Ϫ (ec1 ϩ ec3 Ϫ ) (RP2) state with a time constant of 20 ps (43). From luminescence measurements, the free energy difference between the excited state RP* and RP2 was estimated to be ϳ250 meV (49,50), suggesting that the free energy change associated with the formation of RP2 at the expense of RP1 is ϳ190 meV. Finally, the P ϩ A 1…”

Section: Journal Of Biological Chemistry 25223mentioning

confidence: 99%

The Thermodynamics and Kinetics of Electron Transfer between Cytochrome b6f and Photosystem I in the Chlorophyll d-dominated Cyanobacterium, Acaryochloris marina

Bailleul

Johnson

Finazzi

et al. 2008

Journal of Biological Chemistry

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We have investigated the photosynthetic properties of Acaryochloris marina, a cyanobacterium distinguished by having a high level of chlorophyll d, which has its absorption bands shifted to the red when compared with chlorophyll a. Despite this unusual pigment content, the overall rate and thermodynamics of the photosynthetic electron flow are similar to those of chlorophyll a-containing species. The midpoint potential of both cytochrome f and the primary electron donor of photosystem I (P 740 ) were found to be unchanged with respect to those prevailing in organisms having chlorophyll a, being 345 and 425 mV, respectively. Thus, contrary to previous reports (Hu, Q., Miyashita, H., Iwasaki, I. I., Kurano, N., Miyachi, S., Iwaki, M., and Itoh, S. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 13319 -13323), the midpoint potential of the electron donor P 740 has not been tuned to compensate for the decrease in excitonic energy in A. marina and to maintain the reducing power of photosystem I. We argue that this is a weaker constraint on the engineering of the oxygenic photosynthetic electron transfer chain than preserving the driving force for plastoquinol oxidation by P 740 , via the cytochrome b 6 f complex. We further show that there is no restriction in the diffusion of the soluble electron carrier between cytochrome b 6 f and photosystem I in A. marina, at variance with plants. This difference probably reflects the simplified ultrastructure of the thylakoids of this organism, where no segregation into grana and stroma lamellae is observed. Nevertheless, chlorophyll fluorescence measurements suggest that there is energy transfer between adjacent photosystem II complexes but not from photosystem II to photosystem I, indicating spatial separation between the two photosystems.Acaryochloris marina is an unusual cyanobacterium, because it contains mainly chlorophyll (Chl) 3 d. It was first isolated from a suspension of algae squeezed out of Lissoclinum patella, a colonial ascidian (1). It mainly grows as a biofilm on the undersurface of the ascidian beneath a symbiotic layer of a Prochloron, which is in the upper tunic of the ascidian (2). Other varieties of Acaryochloris have been found on the underside of the thallus of red algae (3) and free living in a salt lake (4). The general feature of its habitat is that it lives at relatively low light intensities, which are enriched in the far red region of the spectrum. Therefore, its oxygenic photosynthesis provides a typical example of adaptation to specific light conditions (2), as evidenced by its pigment composition, where Chl d is predominant and the Chl a level is very low (5, 6). This pigment composition contrasts with the usual high level of Chl a found in other oxygenic phototrophes, as illustrated by the absorption spectrum of a suspension of A. marina cells, which is markedly red-shifted when compared with other Chl a-containing photosynthetic organisms. The extent of the red shift of the absorption spectrum of A. marina is of similar magnitude to that observed b...

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Thermodynamical and structural information on photosynthetic systems obtained from electroluminescence kinetics

Cited by 38 publications

References 28 publications

Semi-continuum electrostatic calculations of redox potentials in photosystem I

Semi-continuum electrostatic calculations of redox potentials in photosystem I

Modeling electron transfer in photosystem I

The Thermodynamics and Kinetics of Electron Transfer between Cytochrome b6f and Photosystem I in the Chlorophyll d-dominated Cyanobacterium, Acaryochloris marina

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