Reaction Center Associated Cytochromes

Nitschke, Wolfgang; Dracheva, Stella

doi:10.1007/0-306-47954-0_36

Cited by 36 publications

(40 citation statements)

References 130 publications

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“…In line with the fact that UQ is the dominant quinone species in ␣/␤/␥-proteobacteria, all electron transport chains characterized so far in representatives from these subgroups have been found to be of the HP type (8,11). The only exception to this rule are the ␥-proteobacterial enterobacteria such as Escherichia coli and closely related species that apparently are able to switch between UQ-and MK-based bioenergetic chains in response to varying growth conditions (12).…”

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confidence: 76%

Menaquinone as pool quinone in a purple bacterium

Schoepp‐Cothenet

Lieutaud

Baymann

et al. 2009

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

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114

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Purple bacteria have thus far been considered to operate lightdriven cyclic electron transfer chains containing ubiquinone (UQ) as liposoluble electron and proton carrier. We show that in the purple ␥-proteobacterium Halorhodospira halophila, menaquinone-8 (MK-8) is the dominant quinone component and that it operates in the QB-site of the photosynthetic reaction center (RC). The redox potentials of the photooxidized pigment in the RC and of the Rieske center of the bc1 complex are significantly lower (Em ‫؍‬ ؉270 mV and ؉110 mV, respectively) than those determined in other purple bacteria but resemble those determined for species containing MK as pool quinone. These results demonstrate that the photosynthetic cycle in H. halophila is based on MK and not on UQ. This finding together with the unusual organization of genes coding for the bc1 complex in H. halophila suggests a specific scenario for the evolutionary transition of bioenergetic chains from the low-potential menaquinones to higher-potential UQ in the proteobacterial phylum, most probably induced by rising levels of dioxygen 2.5 billion years ago. This transition appears to necessarily proceed through bioenergetic ambivalence of the respective organisms, that is, to work both on MK-and on UQ-pools. The establishment of the corresponding low-and high-potential chains was accompanied by duplication and redox optimization of the bc1 complex or at least of its crucial subunit oxidizing quinols from the pool, the Rieske protein. Evolutionary driving forces rationalizing the empirically observed redox tuning of the chain to the quinone pool are discussed.electron transport ͉ evolution ͉ photosynthesis C hemiosmotic energy-converting mechanisms in all life on this planet are variations on a strikingly conserved theme. Electrons derived from reduced substrates enter a chain of membrane-integral and/or associated enzymes and are channeled on toward terminal electron-accepting substrates. Some of the free energy available during individual electron-transfer steps is stored in a transmembrane proton motive gradient. Mitchell (1) proposed a general mechanism for coupling electron transfer to proton translocation, which accounts for the majority of these systems. In this mechanism, electrons travel through 2 types of carrier ''arms'' back and forth across the energetic membrane. In an ''electrogenic arm,'' electrons move alone across the membrane from the positively to the negatively charged side, building up an electric field. Via a ''neutral arm,'' electrons travel in the opposite direction, along with protons. Placing electrogenic and neutral arms in series leads to net proton translocation across the membrane.Without exception, the chemiosmotic neutral arms involve diffusion of small, lipophilic molecules across the energetic membrane. In all bioenergetic systems except methanogenesis, these molecules are quinones that diffuse in the lipid bilayer. The bulk of these diffusing quinones electrochemically connecting redox enzymes is called the quinone pool, to disti...

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confidence: 76%

Menaquinone as pool quinone in a purple bacterium

Schoepp‐Cothenet

Lieutaud

Baymann

et al. 2009

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

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114

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“…PH S00 1 4-5793(96)00382-1 [20]. Two of the hemes show high Em values and the other two hemes show low Em values.…”

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confidence: 99%

Shortcut of the photosynthetic electron transfer in a mutant lacking the reaction center‐bound cytochrome subunit by gene disruption in a purple bacterium, Rubrivivax gelatinosus

1996

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A mutant lacking the reaction center-bound cytochrome subunit was constructed in a purple photosynthetic bacterium, Rubrivivax gelatinosus IL144, by inactivation of the cytochrome gene. Photosynthetic growth of the C244 mutant strain occurred at approximately half the rate of the wild-type strain. Although mutagenesis resulted in a greatly reduced amount of memhrane-bound cytochromes c, illumination induced cyclic electron transfer and the generation of membrane potential in the mutant as observed in the wild-type strain. These fmdings are consistent with previous observations that the cytochrome subunit is absent in the reaction center complex in some species of purple bacteria and that the biochemical removal of the subunit did not significantly affect the in vitro electron transfer from the soluble cytochrome c to the photosynthetic reaction center. These results suggest that the cytochrome subunit in purple bacteria is not essential for photosynthetic electron transfer and growth, even in those species generally containing the subunit.

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“…1 Upon absorption of a photon by the RC, an electron is transferred from a primary electron donor, located on the periplasmic side of the membrane, to an acceptor on the cytoplasmic side. In purple photosynthetic bacteria the primary electron donor is a bacteriochlorophyll dimer (P), and the electron acceptor a quinone molecule (Q A ).…”

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“…1). Three-dimensional highresolution structures of the RC and its associated cytochrome subunit have been determined for Blastochloris (formerly Rhodopseudomonas) viridis (2) and Thermochromatium tepidum (3).…”

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Structural and Functional Characterization of the Unusual Triheme Cytochrome Bound to the Reaction Center of Rhodovulum sulfidophilum

Alric

Tsukatani

Yoshida

et al. 2004

Journal of Biological Chemistry

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The cytochrome bound to the photosynthetic reaction center of Rhodovulum sulfidophilum presents two unusual characteristics with respect to the well characterized tetraheme cytochromes. This cytochrome contains only three hemes because it lacks the peptide motif CXXCH, which binds the most distal fourth heme. In addition, we show that the sixth axial ligand of the third heme is a cysteine (Cys-148) instead of the usual methionine ligand. This ligand exchange results in a very low midpoint potential (؊160 ؎ 10 mV). The influence of the unusual cysteine ligand on the midpoint potential of this distal heme was further investigated by site-directed mutagenesis. The midpoint potential of this heme is upshifted to ؉310 mV when cysteine 148 is replaced by methionine, in agreement with the typical redox properties of a His/Met coordinated heme. Because of the large increase in the midpoint potential of the distal heme in the mutant, both the native and modified high potential hemes are photooxidized at a redox poise where only the former is photooxidizable in the wild type. The relative orientation of the three hemes, determined by EPR measurements, is shown different from tetraheme cytochromes. The evolutionary basis of the concomitant loss of the fourth heme and the down-conversion of the third heme is discussed in light of phylogenetic relationships of the Rhodovulum species triheme cytochromes to other reaction center-associated tetraheme cytochromes.

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Reaction Center Associated Cytochromes

Cited by 36 publications

References 130 publications

Menaquinone as pool quinone in a purple bacterium

Menaquinone as pool quinone in a purple bacterium

Shortcut of the photosynthetic electron transfer in a mutant lacking the reaction center‐bound cytochrome subunit by gene disruption in a purple bacterium, Rubrivivax gelatinosus

Structural and Functional Characterization of the Unusual Triheme Cytochrome Bound to the Reaction Center of Rhodovulum sulfidophilum

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