Dimeric ubiquinol:cytochrome <i>c</i> reductase of <i>Neurospora</i> mitochondria contains one cooperative ubiquinone‐reduction centre

Linke, Petra; Bechmann, Georg; Gothe, Alexander; Weiss, Hanns

doi:10.1111/j.1432-1033.1986.tb09799.x

Cited by 36 publications

(13 citation statements)

References 34 publications

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“…In the absence of endogenous ubiquinone we no longer observed the triphasic reduction of cytochrome b, but upon ubiquinone addition triphasic reduction was restored. These results agree with previous studies, in which extraction of ubiquinone from the cytochrome bc 1 complex eliminated triphasic reduction (20), and triphasic reduction was restored upon ubiquinone addition (21). Our finding that the rates of the three phases depend on the ubiquinone content of the bc 1 complex explains why in some instances the reaction was reportedly biphasic (20).…”

Section: Discussionsupporting

confidence: 93%

“…The most obvious difference in the pre-steady state reduction of the bc 1 complex from the mutant lacking endogenous ubiquinone is that reduction of cytochrome b is not triphasic but rather a rapid monophasic reaction. A similar lack of triphasic reduction was reported in two previous studies (20,21). With 6 M menaquinol the rate of cytochrome b reduction was monophasic and occurred at 9.1 Ϯ 1.9 s Ϫ1 .…”

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confidence: 87%

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Ubiquinone at Center N Is Responsible for Triphasic Reduction of Cytochrome b in the Cytochromebc 1 Complex

Snyder

Trumpower

1999

Journal of Biological Chemistry

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We have examined the pre-steady state reduction kinetics of the Saccharomyces cerevisiae cytochrome bc 1 complex by menaquinol in the presence and absence of endogenous ubiquinone to elucidate the mechanism of triphasic cytochrome b reduction. With cytochrome bc 1 complex from wild type yeast, cytochrome b reduction was triphasic, consisting of a rapid partial reduction phase, an apparent partial reoxidation phase, and a slow rereduction phase. Absorbance spectra taken by rapid scanning spectroscopy at 1-ms intervals before, during, and after the apparent reoxidation phase showed that this was caused by a bona fide reoxidation of cytochrome b and not by any negative spectral contribution from cytochrome c 1 . With cytochrome bc 1 complex from a yeast mutant that cannot synthesize ubiquinone, cytochrome b reduction by either menaquinol or ubiquinol was rapid and monophasic. Addition of ubiquinone restored triphasic cytochrome b reduction, and the duration of the reoxidation phase increased as the ubiquinone concentration increased. When reduction of the cytochrome bc 1 complex through center P was blocked, cytochrome b reduction through center N was biphasic and was slowed by the addition of exogenous ubiquinone. These results show that ubiquinone residing at center N in the oxidized cytochrome bc 1 complex is responsible for the triphasic reduction of cytochrome b.Although the protonmotive Q cycle mechanism of the cytochrome bc 1 complex is generally well understood (1-3), the redox behavior of cytochrome b during pre-steady state reduction of the bc 1 complex is not fully understood. Cytochrome b reduction is triphasic, consisting of a rapid partial reduction phase, a partial reoxidation phase, and a slow rereduction phase. This behavior is puzzling, because the reoxidation phase occurs while reduced substrate is still available, and continued reduction of cytochrome b would be expected.Previous examinations of the pre-steady state reduction kinetics of the bc 1 complex were limited to single wavelength kinetics, and the spectral data, when collected, extended over time ranges that were long relative to the half-times of the reactions (4 -9). The substrates used in these studies, succinate, duroquinol, trimethylquinol, and ubiquinol, have relatively high redox potentials and reduce only a small percentage of cytochrome b. This is of concern because the high redox potential may predispose these substrates to oxidize cytochrome b and thus introduce artifacts into the pre-steady state kinetics in the absence of a low potential reductant.Several explanations for the triphasic reduction have been put forth. One proposal is that ubiquinone formed at center P is not in rapid equilibration with the quinone pool and oxidizes cytochrome b at center N (5, 10). Crystal structures of the mitochondrial cytochrome bc 1 complexes show a pear-shaped and dimeric integral membrane protein that extends ϳ80 Å into the matrix and ϳ30 Å into the intermembrane space (11, 12). There are two large cavities within the bc 1 dimer that lin...

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Section: Discussionsupporting

confidence: 93%

supporting

confidence: 87%

Ubiquinone at Center N Is Responsible for Triphasic Reduction of Cytochrome b in the Cytochromebc 1 Complex

Snyder

Trumpower

1999

Journal of Biological Chemistry

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“…There is widespread agreement that the mitochondrial cytochrome bcl complex can function as a structural and functional dimer (von Jagow & Sebald, 1980;Linke et al, 1986;Schmitt & Trumpower, 1990;Schiigger & von Jagow, 1991;Nieboer & Berden, 1992), although there is disagreement over whether the dimeric form is obligatory (Schagger & von Jagow, 1991) or whether monomer and dimer forms coexist and their interconversion is important in the regulation and mechanism of electron transport (Schmitt & Trumpower, 1990). Although evidence for a structural dimer (Morschel & Staehelin, 1983) and for two centrifugally separableforms, presumably monomer and dimer (Chain & Malkin, 1991), has been presented, it has also been argued on the basis of inhibitor stoichiometry that the bdfcomplex can function as a monomer (Rich et al, 1991).…”

Section: Resultsmentioning

confidence: 99%

“…(ii) The dimeric bcl complex (a) has a very high (ca. lo3 s-l) rate of cytochrome c reductase activity in the presence of saturating amounts of lipid (Schagger et al, 1990) and (b) can mediate proton translocation activity with an H+/e ratio = 1.8 when reconstituted into liposomes at a quinone/complex ratio of 0.5 (Linke et al, 1986). The latter data were interpreted in the context of an alternating "Q cycle" model with the single Q shared by the two protomers each containing two hemes b and an iron-sulfur center.…”

mentioning

confidence: 99%

Characterization of the Chloroplast Cytochrome b6f Complex as a Structural and Functional Dimer

Huang¹,

Everly²,

Cheng³

et al. 1994

Biochemistry

133

100

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Size analysis of the cytochrome bdcomplex by FPLC Superose-12 chromatography and Blue Native PAGE indicated a predominantly dimeric component with M, = (1.9-2.5) X lo5. The true dimer molecular weight including bound lipid, but not detergent, was estimated to be 2.3 X lo5. Size and shape analysis by negative-stain single-particle electron microscopy indicated that the preparation of dimeric complexes contains a major population that has a protein cross section 40% larger than the monomer, binds more negative stain, and has a geometry with a distinct 2-fold axis of symmetry compared to the monomeric complex. The dimeric species is more stable at higher ionic strength with respect to conversion to the monomeric species. SDS-PAGE of monomer and dimer preparations indicated that both contain the four major polypeptides in approximately equal stoichiometry and also contain thepetG M, 4000 subunit. One bound chlorophyll a per monomer, part of the bound lipid, is present in monomer and dimer. The in vitro electron-transport activity (decyl-PQHz -PC-ferricyanide) of the separated dimer was comparable to that of the isolated bdcomplex and was 4-5-fold greater than that of the monomer preparation, whose activity could be attributed to residual dimer. No difference in the properties of the dimer and monomer was detected by SDS-PAGE or redox difference spectrophotometry that could account for the difference in activities. However, the concentration of the Rieske [2Fe-2S] center was found by EPR analysis of the g , = 1.90 signal to be lower in the monomer fraction by a factor of 3.5 relative to the dimer. The presence of active dimer at high levels in the detergent-extracted bdcomplex, the absence of activity in the monomer, and the absence of a monomer preparation that is not degraded in its spectral properties and activity suggest that the simplest inference is that the dimer is the active complex in the membrane. The possibility that cytochrome b d and bcl are primitive trans-membrane-signaling complexes is noted.The cytochrome bsf complex is one of three integral membrane protein complexes involved in electron transport in membranes that carry out oxygenic photosynthesis. The bsfcomplex occupies an electrochemically central position in the noncyclic electron-transport chain, accepting electrons from the photosystem I1 reaction center that is associated with 0 2 evolution, and donating them to the photosystem I reaction center that reduces ferredoxin and nicotinamide adenine dinucleotide phosphate (NADP+). The bsfcomplex bears many similarities to the cytochrome bcl complex of the

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“…A light form of the beef heart complex, with a Stokes radius corresponding to that of a monomer, was reversibly obtained by varying either the salt or detergent concentrations and was reported to be active (34,36,42). Titration of the complex with various inhibitors, on the other hand, led to the conclusion that the functional unit of the bc 1 complex is a dimer (43)(44)(45)(46). It has been proposed that an equilibrium between monomer and dimer plays a role in regulating electron transport in vivo (28,42,44).…”

mentioning

confidence: 99%

Dimer to Monomer Conversion of the Cytochromeb6 f Complex

Breyton¹,

Tribet²,

Olive³

et al. 1997

Journal of Biological Chemistry

139

173

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The molecular weight of the cytochrome b 6 f complex purified from Chlamydomonas reinhardtii thylakoid membranes has been determined by combining velocity sedimentation measurements, molecular sieving analyses, and determination of its lipid and detergent content. The complex in its enzymatically active form is a dimer. Upon incubation in detergent solution, it converts irreversibly into an inactive, monomeric form that has lost the Rieske iron-sulfur protein, the b 6 f-associated chlorophyll, and, under certain conditions, the small 32-residue subunit PetL. The results are consistent with the view that the dimer is the predominant form of the b 6 f in situ while the monomer observed in detergent solution is a breakdown product. Indirect observations suggest that subunit PetL plays a role in stabilizing the dimeric state. Delipidation is shown to be a critical factor in detergent-induced monomerization.

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Dimeric ubiquinol:cytochrome c reductase of Neurospora mitochondria contains one cooperative ubiquinone‐reduction centre

Cited by 36 publications

References 34 publications

Ubiquinone at Center N Is Responsible for Triphasic Reduction of Cytochrome b in the Cytochromebc 1 Complex

Ubiquinone at Center N Is Responsible for Triphasic Reduction of Cytochrome b in the Cytochromebc 1 Complex

Characterization of the Chloroplast Cytochrome b6f Complex as a Structural and Functional Dimer

Dimer to Monomer Conversion of the Cytochromeb6 f Complex

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