Demonstration of a collisional interaction of ubiquinol with the ubiquinol-cytochrome c2 oxidoreductase complex in chromatophores from Rhodobacter sphaeroides

Venturoli, Giovanni; Fernández-Velasco, Javier G.; Crofts, Antony R.; Melandri, B. Andrea

doi:10.1016/0005-2728(86)90070-8

Cited by 70 publications

(36 citation statements)

References 24 publications

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“…The initial rate remains low and approximately constant until the E h is lowered to about 100 mV; below this value the rate increases very steeply and is stimulated more than tenfold at Eh,7,8 = 50 mV. This experiment demonstrates clearly the pool function of the ubiquinone dissolved in the phospholipid phase, since, as discussed in [7] and [29], the stimulation of the rate at relatively low Eh is related to an increase in the collision frequency of ubiquinol at the QZ site. These results are in excellent agreement with data previously obtained in chromatophores, when the pH dependence of the Em of ubiquinone (-60 mV/pH unit) is taken into account.…”

Section: Resultssupporting

confidence: 56%

Kinetics of photosynthetic electron transfer in artificial vesicles reconstituted with purified complexes from Rhodobacter capsulatus

Venturoli

Gabellini²,

Oesterhelt³

et al. 1990

European Journal of Biochemistry

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1. The cyclic photosynthetic chain of Rhodobacter capsulatus has been reconstituted incorporating into phospholipid liposomes containing ubiquinone-10 two multiprotein complexes: the reaction center and the ubiquinol -cyctochrome-c2 reductase (or bel complex).2. In the presence of cytochrome c2 added externally, at concentrations in the range 10-lo4 nM, a flashinduced cyclic electron transfer can be observed. In the presence of antimycin, an inhibitor of the quinone-reducing site of the bel complex, the reduction of cytochrome b561 is a consequence of the donation of electrons to the photo-oxidized reaction center. At low ionic strength (10 mM KCl) and at concentrations of cyctochrome c2 lower than 1 pM, the rate of this reaction is limited by the concentration of cytochrome c2. At higher concentrations the reduction rate of cytochrome b561 is controlled by the concentration of quinol in the membrane, and, therefore, is increased when the ubiquinone pool is progressively reduced. At saturating concentrations of cytochrome c2 and optimal redox poise, the half-time for cytochrome b561 reduction is about 3 ms.3. At high ionic stength (200 mM KCl), tenfold higher concentrations of cytochrome c2 are required for promoting equivalent rates of cytochrome-b561 reduction. If the absolute values of these rates are compared with those of the cytochrome-c2 -reaction-center electron transfer, it can be concluded that the reaction of oxidized cytochrome c2 with the bel complex is rate-limiting and involves electrostatic interactions.4. A significant rate of intercomplex electron transfer can be observed also in the absence of cytochrome c 2 ; in this case the electron donor to the recation center is the cytochrome c1 of the oxidoreductase complex. The oxidation of cytochrome c1 triggers a normal electron transfer within the bel complex. The intercomplex reaction follows second-order kinetics and is slowed at high ionic strength, suggesting a collisional interaction facilitated by electrostatic attraction. From the second-order rate constant of this process, a minimal bidimensional diffusion coefficient for the complexes in the membrane equal to 3 x lo-" cm2 sK1 can be evaluated.In photosynthetic membranes of purple bacteria, such as Rhodobacter capsulatus, the secondary electron transfer around the photosynthetic reaction center (RC) is essentially catalyzed by the ubiquinol -cytochrome-c2 oxidoreductase complex (also known as bel complex). This complex is formed by three subunits and contains four redox centers: a Fe2S2 cluster (Em,7 = 310 mV, pH-independent [I]) and a cytochrome of the c type (cytochrome el, Em,7 = 285 mV, pHindependent [2]) contained in two largely hydrophilic domains; two 6-type hemes [cytochrome b561, Em,7 = 50 mV Abbreviations. BChl, bacteriochlorophyll; bcl, ubiquinolcytochrome-c reductase; Eh, ambient oxidoreduction potential relative to the normal hydrogen electrode; Em,,, midpoint oxidationreduction potential at p H = x ; RC, reaction center; UHDBT, 5-nundecyl-6-hydroxy-4,7-dioxo benzothiazole. phot...

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Section: Resultssupporting

confidence: 56%

Kinetics of photosynthetic electron transfer in artificial vesicles reconstituted with purified complexes from Rhodobacter capsulatus

Venturoli

Gabellini²,

Oesterhelt³

et al. 1990

European Journal of Biochemistry

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“…This conclusion is also fully justified by antimycin A inhibition of the process (Fig. 1, 4, and 6) and by considering that, under conditions of steady-state respiration or photosynthesis, membranes of R. capsulatus contain an excess of QH 2 molecules (19,42,49,50,52).…”

Section: Discussionmentioning

confidence: 81%

The Thiol:Disulfide Oxidoreductase DsbB Mediates the Oxidizing Effects of the Toxic Metalloid Tellurite (TeO₃²⁻) on the Plasma Membrane Redox System of the Facultative PhototrophRhodobacter capsulatus

et al. 2007

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The highly toxic oxyanion tellurite (TeO 3 2؊ ) is a well known pro-oxidant in mammalian and bacterial cells. This work examines the effects of tellurite on the redox state of the electron transport chain of the facultative phototroph Rhodobacter capsulatus, in relation to the role of the thiol:disulfide oxidoreductase DsbB. Under steady-state respiration, the addition of tellurite (2.5 mM) to membrane fragments generated an extrareduction of the cytochrome pool (c-and b-type hemes); further, in plasma membranes exposed to tellurite (0.25 to 2.5 mM) and subjected to a series of flashes of light, the rate of the QH 2 :cytochrome c (Cyt c) oxidoreductase activity was enhanced. The effect of tellurite was blocked by the antibiotics antimycin A and/or myxothiazol, specific inhibitors of the QH 2 :Cyt c oxidoreductase, and, most interestingly, the membrane-associated thiol: disulfide oxidoreductase DsbB was required to mediate the redox unbalance produced by the oxyanion. Indeed, this phenomenon was absent from R. capsulatus MD22, a DsbB-deficient mutant, whereas the tellurite effect was present in membranes from MD22/pDsbB WT , in which the mutant gene was complemented to regain the wild-type DsbB phenotype. These findings were taken as evidence that the membrane-bound thiol:disulfide oxidoreductase DsbB acts as an "electron conduit" between the hydrophilic metalloid and the lipid-embedded Q pool, so that in habitats contaminated with subinhibitory amounts of Te IV , the metalloid is likely to function as a disposal for the excess reducing power at the Q-pool level of facultative phototrophic bacteria.In the environment, tellurium (Te) exists in its elementalTe 0 -inorganic-telluride (Te 2Ϫ ), tellurite (TeO 3 2Ϫ ), and tellurate (TeO 4 2Ϫ )-and organic-dimethyl telluride (CH 3 TeCH 3 )-forms (8). Of these, the toxic oxyanion forms, TeO 3 2Ϫ and TeO 4 2Ϫ , are more common than and are highly soluble compared to nontoxic elemental tellurium, Te 0 (38). Tellurium is widely used in the electronics industry, for photoreceptors, thermocouples, and batteries, but also in metallurgical processes and as an additive to industrial glasses (8). As a result, microorganisms are now becoming exposed to abnormal concentrations of this element, and bacterial species resistant to tellurium can easily be isolated from industrial sludge (38). However, research into the anthropogenic emission of Tebased compounds is scarce, and the implications for selection of microorganisms resistant to tellurite (TeO 3 2Ϫ ) and tellurate (TeO 4 2Ϫ ) are largely unexplored (40). Tellurite is more toxic to mammalian cells (43) and microorganisms (38) than are several heavy metals, e.g., mercury, cadmium, zinc, chromium, and cobalt, which are objects of major public health concern (38). Depending on the strain, the concentration of tellurite inhibiting microbial growth ranges from 1 to 1,000 g/ml (34,38,(46)(47)(48). Microorganisms counteract tellurite (TeO 3 2Ϫ ) toxicity in several ways, namely, by (i) decreasing its uptake, (ii) enhancing its effl...

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“…By investigating the second-order reduction of cytochrome b561 in chromatophores by the quinol produced by photoreduction in the reaction center at different redox poise of the quinone pool, a substrate-like dependence of the rate on ubiquinol concentration was found with an apparent Km for ubiquinol-10 of 7 mM in the phospholipids (Venturoli et al, 1987).…”

Section: Mitochondrial Electron Transfer Is Coupled To Ubiquinone Difmentioning

confidence: 99%

Role of mobility of redox components in the inner mitochondrial membrane

Lenaz

1988

J. Membrain Biol.

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Demonstration of a collisional interaction of ubiquinol with the ubiquinol-cytochrome c2 oxidoreductase complex in chromatophores from Rhodobacter sphaeroides

Cited by 70 publications

References 24 publications

Kinetics of photosynthetic electron transfer in artificial vesicles reconstituted with purified complexes from Rhodobacter capsulatus

Kinetics of photosynthetic electron transfer in artificial vesicles reconstituted with purified complexes from Rhodobacter capsulatus

The Thiol:Disulfide Oxidoreductase DsbB Mediates the Oxidizing Effects of the Toxic Metalloid Tellurite (TeO₃²⁻) on the Plasma Membrane Redox System of the Facultative PhototrophRhodobacter capsulatus

Role of mobility of redox components in the inner mitochondrial membrane

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Demonstration of a collisional interaction of ubiquinol with the ubiquinol-cytochrome c2 oxidoreductase complex in chromatophores from Rhodobacter sphaeroides

Cited by 70 publications

References 24 publications

Kinetics of photosynthetic electron transfer in artificial vesicles reconstituted with purified complexes from Rhodobacter capsulatus

Kinetics of photosynthetic electron transfer in artificial vesicles reconstituted with purified complexes from Rhodobacter capsulatus

The Thiol:Disulfide Oxidoreductase DsbB Mediates the Oxidizing Effects of the Toxic Metalloid Tellurite (TeO32−) on the Plasma Membrane Redox System of the Facultative PhototrophRhodobacter capsulatus

Role of mobility of redox components in the inner mitochondrial membrane

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The Thiol:Disulfide Oxidoreductase DsbB Mediates the Oxidizing Effects of the Toxic Metalloid Tellurite (TeO₃²⁻) on the Plasma Membrane Redox System of the Facultative PhototrophRhodobacter capsulatus