Two distinct quinone‐modulated modes of antimycin‐sensitive cytochrome b reduction in the cytochrome bc1 complex

Robertson, Dan E.; Giangiacomo, Kathleen M.; Vries, Simon de; Moser, Christopher C.; Dutton, P. Leslie

doi:10.1016/0014-5793(84)80630-4

Cited by 44 publications

(16 citation statements)

References 35 publications

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“…To estimate the affinity constant, Δ U H T of AGPS was calculated according to equation 6 [13] using ThermoFAD output, and Δ U C p was estimated according to AGPS size and structure [19]. The calculation of the estimated Kd was performed according to equation 14 [13], intentionally considering a range of uncertainty due to the reasonable assumption of Δ b H Tm being 40 kJ/mol (relatively unimportant for the overall Kd calculation).…”

Section: Methodsmentioning

confidence: 99%

Discovery of Inhibitors for the Ether Lipid-Generating Enzyme AGPS as Anti-Cancer Agents

et al. 2015

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Dysregulated ether lipid metabolism is an important hallmark of cancer cells. Previous studies have reported that lowering ether lipid levels by genetic ablation of the ether lipid-generating enzyme alkyl-glycerone phosphate synthase (AGPS) lowers key structural and oncogenic ether lipid levels and alters fatty acid, glycerophospholipid, and eicosanoid metabolism to impair cancer pathogenicity, indicating that AGPS may be a potential therapeutic target for cancer. In this study, we have performed a small-molecule screen to identify candidate AGPS inhibitors. We have identified several lead AGPS inhibitors and have structurally characterized their interactions with the enzyme and show that these inhibitors bind to distinct portions of the active site. We further show that the lead AGPS inhibitor 1a selectively lowers ether lipid levels in several types of human cancer cells and impairs their cellular survival and migration. We provide here the first report of in situ-effective pharmacological tools for inhibiting AGPS, which may provide chemical scaffolds for future AGPS inhibitor development for cancer therapy.

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Section: Methodsmentioning

confidence: 99%

Discovery of Inhibitors for the Ether Lipid-Generating Enzyme AGPS as Anti-Cancer Agents

et al. 2015

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“…(3) QH2 Oxidation at the Q¡ Site. At alkaline pH values and in the presence of the Q0 site inhibitor myxothiazol, it has been demonstrated that it is both thermodynamically and kinetically feasible for QH2 at the Q¡ site to reduce cyt bu Robertson et al, 1984a; Figure 7, event 3). The details of the reaction are unclear, but it appears to be either an equilibration of QH2 in the pool with cyt bu or a direct interaction of Qb with cyt bu-We took advantage of this pathway of electron transfer between QH2 at the Q¡ site and cyt bu to compare the rates and extents of cyt ¿>h reduction in the wild-type and mutant strains.…”

Section: Methodsmentioning

confidence: 99%

Requirement of histidine 217 for ubiquinone reductase activity (Qi site) in the cytochrome bc1 complex

Gray

Dutton²,

Daldal³

1994

Biochemistry

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Folding models suggest that the highly conserved histidine 217 of the cytochrome b subunit from the cytochrome bc1 complex is close to the quinone reductase (Qi) site. This histidine (bH217) in the cytochrome b polypeptide of the photosynthetic bacterium Rhodobacter capsulatus has been replaced with three other residues, aspartate (D), arginine (R), and leucine (L). bH217D and bH217R are able to grow photoheterotrophically and contain active cytochrome bc1 complexes (60% of wild-type activity), whereas the bH217L mutant is photosynthetically incompetent and contains a cytochrome bc1 complex that has only 10% of the wild-type activity. Single-turnover flash-activated electron transfer experiments show that cytochrome bH is reduced via the Qo site with near native rates in the mutant strains but that electron transfer between cytochrome bH and quinone bound at the Qi site is greatly slowed. These results are consistent with redox midpoint potential (Em) measurements of the cytochrome b subunit hemes and the Qi site quinone. The Em values of cyt bL and bH are approximately the same in the mutants and wild type, although the mutant strains have a larger relative concentration of what may be the high-potential form of cytochrome bH, called cytochrome b150. However, the redox properties of the semiquinone at the Qi site are altered significantly. The Qi site semiquinone stability constant of bH217R is 10 times higher than in the wild type, while in the other two strains (bH217D and bH217L) the stability constant is much lower than in the wild type. Thus H217 appears to have major effects on the redox properties of the quinone bound at the Qi site. These data are incorporated into a suggestion that H217 forms part of the binding pocket of the Qi site in a manner reminiscent of the interaction between quinone bound at the Qb site and H190 of the L subunit of the bacterial photosynthetic reaction center.

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“…Therefore the heme b h could be reduced via center N by the RC-generated ubiquinol in the presence of myxothiazol at pH > 8.0. 90, 91 The reaction was accompanied by a blue carotenoid bandshift indicating a discharge of Dw; this shift was not observed in the presence of antimycin. 73,88 This negative electrogenesis was more pronounced in the presence of Dw.…”

Section: Electrogenic Reactions In Bcmentioning

confidence: 98%

Proton translocation by the cytochrome bc1 complexes of phototrophic bacteria: introducing the activated Q-cycle

Mulkidjanian

2007

Photochem Photobiol Sci

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The cytochrome bc1 complexes are proton-translocating, dimeric membrane ubiquinol:cytochrome c oxidoreductases that serve as "hubs" in the vast majority of electron transfer chains. After each ubiquinol molecule is oxidized in the catalytic center P at the positively charged membrane side, the two liberated electrons head out, according to the Mitchell's Q-cycle mechanism, to different acceptors. One is taken by the [2Fe-2S] iron-sulfur Rieske protein to be passed further to cytochrome c1. The other electron goes across the membrane, via the low- and high-potential hemes of cytochrome b, to another ubiquinone-binding site N at the opposite membrane side. It has been assumed that two ubiquinol molecules have to be oxidized by center P to yield first a semiquinone in center N and then to reduce this semiquinone to ubiquinol. This review is focused on the operation of cytochrome bc1 complexes in phototrophic purple bacteria. Their membranes provide a unique system where the generation of membrane voltage by light-driven, energy-converting enzymes can be traced via spectral shifts of native carotenoids and correlated with the electron and proton transfer reactions. An "activated Q-cycle" is proposed as a novel mechanism that is consistent with the available experimental data on the electron/proton coupling. Under physiological conditions, the dimeric cytochrome bc1 complex is suggested to be continually primed by prompt oxidation of membrane ubiquinol via center N yielding a bound semiquinone in this center and a reduced, high-potential heme b in the other monomer of the enzyme. Then the oxidation of each ubiquinol molecule in center P is followed by ubiquinol formation in center N, proton translocation and generation of membrane voltage.

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Two distinct quinone‐modulated modes of antimycin‐sensitive cytochrome b reduction in the cytochrome bc₁ complex

Cited by 44 publications

References 35 publications

Discovery of Inhibitors for the Ether Lipid-Generating Enzyme AGPS as Anti-Cancer Agents

Discovery of Inhibitors for the Ether Lipid-Generating Enzyme AGPS as Anti-Cancer Agents

Requirement of histidine 217 for ubiquinone reductase activity (Qi site) in the cytochrome bc1 complex

Proton translocation by the cytochrome bc1 complexes of phototrophic bacteria: introducing the activated Q-cycle

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