Coupling of cytochrome and quinone turnovers in the photocycle of reaction centers from the photosynthetic bacterium Rhodobacter sphaeroides

Osváth, Szabolcs; Maróti, Péter

doi:10.1016/s0006-3495(97)78130-x

Cited by 37 publications

(49 citation statements)

References 51 publications

(87 reference statements)

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“…We estimated that at this light intensity, each reaction center complex could absorb about four photons per second (using the results of the calculation in Materials and methods). As the maximum flux through the reaction centers corresponds to a turnover time of 2 ms [45] total saturation with photons should be unexpected, unless their turnover was limited by some other factor. We therefore examined whether the apparent saturation with illumination might be due to a backpressure effect of the Δ ψ on the steady‐state operation of the photosynthetic reaction center, in line with kinetic effects of Δ ψ such as those demonstrated by [17].…”

Section: Resultsmentioning

confidence: 99%

“…This expectation was confirmed by experiments on a soluble system (in the absence of a Δ µ ˜ H + ), using a mixture of purified reaction centers, horse heart cyt c and UQ 6 . When extrapolating to infinitely high light intensities, illumination still had major control on the rates of turnover of the reaction center and cyt c [45]. However the demonstration of backpressure in the experiments described above implies that the same phenomenon should not be expected in the reconstituted system.…”

Section: Discussionmentioning

confidence: 99%

“…The free‐energy of the photons is slightly higher than that recalculated by the method of Parson (84 kJ·mol −1 , correcting for the tenfold higher light intensity and using a k 23 of 10 9 s −1 , rather than 10 11 s −1 ). Using 0.14 MJ for the energy of a mol of 870 nm photons and assuming the maximum turnover rate of the photochemical cycle in the reconstituted core complex system is equal to the maximum turnover rate of the reaction center, with an overall turnover time of ≈ 2 ms [45], the 1.4 nmol of core complexes should be able to absorb at most 0.10 W.…”

Section: Methodsmentioning

confidence: 99%

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Pumping capacity of bacterial reaction centers and backpressure regulation of energy transduction

Rotterdam

Westerhoff²,

Visschers³

et al. 2001

European Journal of Biochemistry

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Transduction of free-energy by Rhodobacter sphaeroides reaction-center-light-harvesting-complex-1 (RCLH1) was quantified. RCLH1 complexes were reconstituted into liposomal membranes. The capacity of the RCLH1 complex to build up a proton motive force was examined at a range of incident light intensities, and induced proton permeabilities, in the presence of artificial electron donors and acceptors. Experiments were also performed with RCLH1 complexes in which the midpoint potential of the reaction center primary donor was modified over an 85-mV range by replacement of the tyrosine residue at the M210 position of the reaction center protein by histidine, phenylalanine, leucine or tryptophan. The intrinsic driving force with which the reaction center pumped protons tended to decrease as the midpoint potential of the primary donor was increased. This observation is discussed in terms of the control of the energetics of the first steps in light-driven electron transfer on the thermodynamic efficiency of the bacterial photosynthetic process. The light intensity at which half of the maximal proton motive force was generated, increased with increasing proton permeability of the membrane. This presents the first direct evidence for so-called backpressure control exerted by the proton motive force on steady-state cyclic electron transfer through and coupled proton pumping by the bacterial reaction center.Keywords: thermodynamics; bacterial photosynthesis; electron transport; reaction center; proton motive force.The fundamental event in photosynthesis is the conversion of light-energy into (Gibbs) free-energy of protons. This process of energy transduction takes place in plants, algae and certain species of bacteria. The transmembrane electron transfer, or charge separation, process occurs in specialized pigment±protein complexes collectively known as photosynthetic reaction centers. The best understood reaction center is that of the purple photosynthetic bacteria, and in particular of the bacterium Rhodobacter sphaeroides. Not only the atomic structure of this reaction center is known [1±3] but it has also been subjected to intensive spectroscopic study. The reaction center (RC) is intimately associated with the LH1 light-harvesting complex, to form the so-called RCLH1`core' complex.In RCLH1 core complexes, the photosynthetic process is initiated by the absorption of a photon, usually by the bacteriochlorophyll (Bchl) or carotenoid molecules of the LH1 antenna that are present in excess over the reaction center pigments. Excitation energy captured by the antenna pigments is transferred to the reaction center on the timescale of a few tens of picoseconds [4], creating the first singlet excited state of the reaction center primary donor, P, (P*) and so transforming P into a powerful reductant that is capable of reducing the adjacent cofactors.Transmembrane electron transfer is a multistep reaction involving the donation of an electron to the (Q A ) ubiquinone-A located within the reaction center protein on the opposite sid...

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Pumping capacity of bacterial reaction centers and backpressure regulation of energy transduction

Rotterdam

Westerhoff²,

Visschers³

et al. 2001

European Journal of Biochemistry

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“…Direct optical detection of cytochrome photooxidation in the cytochrome cycle is a reliable method of tracking the steps of the RC photocycle [22,23]. The oxidation of cytochrome c can be followed by the change in the spectra, i.e., the gradual decrease in the absorption mainly at 550 nm after every flash excitation.…”

Section: Resultsmentioning

confidence: 99%

Light-harvesting bio-nanomaterial using porous silicon and photosynthetic reaction center

et al. 2012

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Porous silicon microcavity (PSiMc) structures were used to immobilize the photosynthetic reaction center (RC) purified from the purple bacterium Rhodobacter sphaeroides R-26. Two different binding methods were compared by specular reflectance measurements. Structural characterization of PSiMc was performed by scanning electron microscopy and atomic force microscopy. The activity of the immobilized RC was checked by measuring the visible absorption spectra of the externally added electron donor, mammalian cytochrome c. PSi/RC complex was found to oxidize the cytochrome c after every saturating Xe flash, indicating the accessibility of specific surface binding sites on the immobilized RC, for the external electron donor. This new type of bio-nanomaterial is considered as an excellent model for new generation applications of silicon-based electronics and biological redox systems.

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“…In these systems, the electron-excited by light-is trapped in the redox system around the RC and, among other things, it can be a part of an electrical circuit segment. This redox system might be used to couple to external redox components and to drive electron transfer reactions [57,58]. There is a large interest in substituting natural redox carriers (cytochrome and quinones) by inorganic carrier matrices, which are able to donate/accept electrons to/from the RC as secondary electron donors/acceptors.…”

Section: Photosynthetic Systems In Bionanotechnologymentioning

confidence: 99%

Functional Nanohybrid Materials from Photosynthetic Reaction Center Proteins

Hajdu

Szabó

Sarrai

et al. 2017

International Journal of Photoenergy

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Application of technical developments in biology and vice versa or biological samples in technology led to the development of new types of functional, so-called "biohybrid" materials. These types of materials can be created at any level of the biological organization from molecules through tissues and organs to the individuals. Macromolecules and/or molecular complexes, membranes in biology, are inherently good representatives of nanosystems since they fall in the range usually called "nano." Nanohybrid materials provide the possibility to create functional bionanohybrid complexes which also led to new discipline called "nanobionics" in the literature and are considered as materials for the future. In this publication, the special characteristics of photosynthetic reaction center proteins, which are "nature's solar batteries," will be discussed in terms of their possible applications for creating functional molecular biohybrid materials.

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Coupling of cytochrome and quinone turnovers in the photocycle of reaction centers from the photosynthetic bacterium Rhodobacter sphaeroides

Cited by 37 publications

References 51 publications

Pumping capacity of bacterial reaction centers and backpressure regulation of energy transduction

Pumping capacity of bacterial reaction centers and backpressure regulation of energy transduction

Light-harvesting bio-nanomaterial using porous silicon and photosynthetic reaction center

Functional Nanohybrid Materials from Photosynthetic Reaction Center Proteins

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