UNIPROT:Q16795 - FACTA Search

Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Target Concepts:

Query: UNIPROT:Q16795 (ubiquinone)
5,455 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The half-time for oxidation of cytochrome b(557) in mitochondria from etiolated mung bean (Phaseolus aureus) hypocotyls is 5.8 milliseconds at 24 Celsius in the absence or presence of 0.3 mm KCN, when the oxidation is carried out by injecting a small amount of oxygenated medium into a suspension of mitochondria made anaerobic in the presence of succinate plus malonate. Since oxygen is consumed by the alternate, cyanide-insensitive respiratory pathway of these mitochondria, cycles of oxidation and reduction can be obtained with the oxygen pulses when cyanide is present. Reduced cytochromes (a + a(3)) also become oxidized at nearly the uninhibited rate under these conditions, a(3) completely and a partially. The half-time for oxidation of c(547) is also unaffected by 0.3 mm KCN, but c(549) has a half-time equal to that of c(547) in the presence of KCN, compared to the shorter one observed in the absence of inhibitor. The maximum extent of oxidation of the cytochromes c is about 70% in the presence of 0.3 mm KCN; this oxidation is rapidly followed by an extensive reduction which is synchronous with the reduction of cytochrome a observed under the same conditions. In the presence of cyanide, it appears likely that the cytochromes c and b(557) are oxidized by cytochrome oxidase in oxygen pulse experiments, rather than by the alternate oxidase. The oxidation of cytochrome b(553) is partially inhibited by KCN, but complete oxidation is attained in the aerobic steady state with excess oxygen. If the oxygen pulse experiment is carried out in the presence of sufficient malonate so that entry of reducing equivalents into the respiratory chain occurs at a rate negligible compared to inter-carrier electron transport, the half-time for flavoprotein oxidation is unaffected by 0.3 mm KCN while that for ubiquinone oxidation is but 2-fold larger. The observed net oxidation rate of these two carriers in mung bean mitochondria is more sensitive to the entry rate of reducing equivalents, as set by succinate concentration and malonate to succinate ratio, then it is in skunk cabbage (Symplocarpus foetidus) mitochondria. These observations are interpreted in terms of a respiratory carrier Y, placed between flavoprotein plus ubiquinone and the cytochromes, which is the fork in the split respiratory pathway to the two terminal oxidases and which has lower electron transport capacity in mung bean mitochondria than in skunk cabbage mitochondria.
...
PMID:The respiratory chain of plant mitochondria. IV. Oxidation rates of the respiratory carriers of mung bean mitochondria in the presence of cyanide. 542 15

The kinetics of oxidation of ubiquinone, flavoprotein, cytochrome c, and the cytochrome b complex in skunk cabbage (Symplocarpus foetidus) mitochondria made anaerobic with succinate have been measured spectrophotometrically and fluorimetrically in the absence of respiratory inhibitor and in the presence of cyanide or antimycin A. No component identifiable by these means was oxidized rapidly enough in the presence of one or the other inhibitor to qualify for the role of alternate oxidase. Cycles of oxidation and rereduction of flavoprotein and ubiquinone obtained by injecting 12 mum oxygen into the anaerobic mitochondrial suspension were kinetically indistinguishable in the presence of cyanide or antimycin A, implying that these 2 components are part of a respiratory pathway between succinate and oxygen which does not involve the cytochromes and does involve a cyanide-insensitive alternate oxidase. The cytochrome b complex shows biphasic oxidation kinetics with half times of 0.018 sec and 0.4 sec in the absence of inhibitor, which increase to 0.2 sec and 1 sec in the presence of cyanide. In the presence of antimycin A, the oxidation of the cytochrome b complex shows an induction period of 1 sec and a half-time of 3.5 sec. A split respiratory chain with 2 terminal oxidases and a branch point between the cytochromes and flavoprotein and ubiquinone is proposed for these mitochondria.
...
PMID:The respiratory chain of plant mitochondria. I. Electron transport between succinate and oxygen in skunk cabbage mitochondria. 577 46

22 revertants of Saccharomyces cerevisiae with intragenic suppressors (supa) of cob exon mutations (G. Burger, Mol. Gen. Genet., in the press) were analyzed. They display either a reduced amount of cytochrome b, or a shifted maximum absorption wavelength of total cytochrome b or a reduced growth rate on glycerol. The relationship of physico-chemical properties (content, light absorption and midpoint potential of cytochromes bK and bT) and functional properties (electron transport and energy yield) has been examined. In seven of eight revertants with a shifted maximum absorption wavelength of cytochrome b neither growth rate nor electron transfer activity was affected. In 13 of 14 revertants, reduced content of cytochrome b corresponds to a reduced electron transport rate through the cytochrome bc1 segment. A lower enzymatic activity, which is not due to a quantitative but to a qualitative alteration of cytochrome b was found in two revertants. Two revertants show electron transport rates of wild-type level concomitant with a reduced growth rate on glycerol, obviously due to a less efficient energy coupling. All revertants were shown to contain a high and a low potential cytochrome b, referred to as bK and bT. Those cob-/supa mutations which shift the maximum absorption wavelength or diminish the content of cytochrome b affect both b cytochromes in all cases. The results support that electron transport and energy conservation are catalyzed by the unity of cytochrome bK and bT and that both heme centers are bound to an identical apoenzyme. Comparing electron flow rates of succinate:cytochrome c oxidoreductase and NADH:cytochrome c oxidoreductase in cob- mutants and two revertants provides evidence that ubiquinone does not constitute a homogeneous pool, suggested by the dissimilar interaction of both dehydrogenases with the bc1 segment.
...
PMID:Cytochrome b of cob revertants in yeast. Bioenergetic characterization of revertants with reduced content and shifted maximum absorption wavelength of cytochrome b. 608 48

We have investigated in detail the effects of dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, DBMIB) on the ubiquinol-cytochrome c reductase (cytochrome bc1 complex) from bovine heart mitochondria. The inhibitory action of DBMIB on the steady-state activity of the bc1 complex is related to the specific binding of the quinone to the purified enzymatic complex. At concentrations higher than 10 mol per mol of the enzyme, DBMIB is able to stimulate an antimycin-insensitive reduction of cytochrome c catalyzed by the bc1 complex. In accordance with kinetic data showing a competition by endogenous ubiquinone in the inhibitory action, DBMIB can be considered as a product-like inhibitor of the ubiquinol-cytochrome c reductase activity. The site of specific binding of dibromothymoquinone in the bc1 complex enables it to interact with the iron-sulphur center of the enzyme, as indicated by changes induced in the EPR spectrum of the center. However, the inhibitor also directly interacts with cytochrome b, promoting a fast chemical oxidation of the reduced heme center. In spite of these effects, DBMIB has been found not to exert significant effects on the first turnover of the fully oxidized bc1 complex, as monitored by the rapid reduction of both cytochromes b and c1 by ubiquinol-1. In the presence of antimycin, only a stimulation of cytochrome c1 reduction, in parallel to an enhanced cytochrome b reoxidation, is observed. Moreover, DBMIB does not affect the oxidant-induced extra cytochrome b reduction in the presence of antimycin. On the basis of the evidences suggesting a competition with the endogenous ubiquinone in the redox cycle of the bc1 complex, a model is proposed for the mechanism of DBMIB inhibition. Such model can also explain at the molecular level the redox bypass induced by dibromothymoquinone in the whole respiratory chain (Degli Esposti, M., Rugolo, M. and Lenaz, G. (1983) FEBS Lett. 156, 15-19).
...
PMID:Effects of dibromothymoquinone on the structure and function of the mitochondrial bc1 complex. 609 48

Reduction of cytochrome b-560 (analogous to cyt b-562 of mitochondria) via an antimycin-sensitive route has been revealed in chromatophores of the photosynthetic bacterium, Rhodopseudomonas sphaeroides Ga. Indeed, the results suggest that two reductive mechanisms can be operative. One is consistent with the idea that the quinol generated at the reaction center QB site enters the Q pool and, via the Qc site, equilibrates with cytochrome b-560. The other reductive mode circumvents redox equilibrium with the pool; we consider that this could result from a direct encounter of the reaction center with the bc1 complex perhaps involving a direct QB-Qc site interaction. This latter reaction is suppressed by occupancy of the Qc site, not only by antimycin but by ubiquinol and ubiquinone.
...
PMID:Two distinct quinone-modulated modes of antimycin-sensitive cytochrome b reduction in the cytochrome bc1 complex. 609 72

The subcellular distribution of cytochrome b and ubiquinone in resting human neutrophils was investigated by rate zonal sedimentation of postnuclear supernatants on continuous sucrose gradients. Both cytochrome b and ubiquinone were mainly localized in small organelles, tertiary granules, that were resolved from the specific and azurophilic granules as well as from the cell membrane fraction. This cytochrome b- and ubiquinone-rich granule was shown to contain dicyclohexylcarbodiimide (DCCD)-sensitive, Mg2+-dependent ATPase as well as low amounts, less than a third, of the acid hydrolases beta-glucuronidase and N-acetyl-beta-glucosaminidase. Cytochrome b was also found in smaller proportions in plasma membranes and specific granules. A significant proportion of the ubiquinone was located in the region of the gradients where specific granules and mitochondria sedimented. However, quantitative measurements of oligomycin-sensitive ATPase indicated that this second localization of ubiquinone could not be entirely attributed to mitochondrial contamination. Plasma membrane contained small amounts of ubiquinone. In addition, the existence and location of a putative proton pump ATPase were also investigated. The ATPase was mainly located in the plasma membrane and in the upper half of the gradients (tertiary and specific granules), with the highest specific activity occurring in the tertiary granules. This activity was inhibited by 100 microM DCCD. Furthermore, ATP-dependent uptake of [14C]methylamine by tertiary and specific granules was observed. These results suggest that the DCCD-sensitive ATPase may function as a proton pump. DCCD inhibited the release of enzymes from specific granules that occurred when human neutrophils were activated by phorbol myristate acetate. However, higher concentrations of DCCD were required to achieve the same degree of inhibition of O2 uptake (I50 of 0.4 mM for secretion versus 1 mM for O2 uptake). These results suggest that specific granules do not play a crucial role in oxygen metabolism.
...
PMID:Subcellular localization of cytochrome b and ubiquinone in a tertiary granule of resting human neutrophils and evidence for a proton pump ATPase. 614 82

The effect of lonidamine, an antispermatogenic and antitumor drug, on the oxygen consumption, ATPase activity, and redox state of the electron carriers of Ehrlich ascites tumor mitochondria has been studied. Lonidamine inhibits ADP- and uncoupler-stimulated respiration on various NAD- and FAD-linked substrates, but does not affect state 4 respiration. Experiments to determine its site of action showed that lonidamine does not significantly inhibit electron flow through cytochrome oxidase. Electron flow through site 2, the ubiquinone-cytochrome b-cytochrome c1 complex, also was unaffected by lonidamine, which failed to inhibit the oxidation of duroquinol. Moreover, inhibition of electron flow through site 2 was also excluded because of the inability of the N,N,N',N'-tetramethyl-p-phenylenediamine bypass to relieve the lonidamine inhibition of the oxidation of pyruvate + malate. The F0F1ATPase activity and vectorial H+ ejection are also unaffected by lonidamine. The inhibition of succinate oxidation by lonidamine was found to take place at a point between succinate and iron-sulfur center S3. Spectroscopic experiments demonstrated that lonidamine inhibits the reduction of mitochondrial NAD+ by pyruvate + malate and other NAD-linked substrates in the transition from state 1 to state 4. However, lonidamine does not inhibit reduction of added NAD+ by submitochondrial vesicles or by soluble purified NAD-linked dehydrogenases. These observations, together with other evidence, suggest that electron transport in tumor mitochondria is inhibited by lonidamine at the dehydrogenase-coenzyme level, particularly when the electron carriers are in a relatively oxidized state and/or when the inner membrane-matrix compartment is in the condensed state. The action of lonidamine in several respects resembles the selective inhibition of electron transport in tumor cells produced by cytotoxic macrophages (D. L. Granger and A. L. Lehninger (1982) J. Cell Biol. 95, 527).
...
PMID:Action of the antitumor and antispermatogenic agent lonidamine on electron transport in Ehrlich ascites tumor mitochondria. 622 86

1. 2-Heptyl-4-hydroxyquinoline-N-oxide (HpHOQnO) binds to oxidized mitochondria of Saccharomyces cerevisiae with a dissociation constant of 5 x 10(-8) M and with a ratio of 1 mol per mol cytochrome b. 2. After addition of 171 micro M ubiquinone-3 to oxidized mitochondria, 0.3 mol HpHOQnO bind to 1 mol cytochrome b. The binding strength of the inhibitor is not essentially affected. 3. Reduction of mitochondria with succinate results in a strong decrease of the HpHOQnO binding. The dissociation constant could not be calculated on the basis of the applied method. 4. On the basis of the inhibitory effect of HpHOQnO on reduced mitochondria, a dissociation constant of 5 x 10(-6) M is calculated. 5. The respiratory electron flow to oxygen is about 100 times as sensitive to HpHOQnO as the electron flow to cytochrome c. 6. Ubiquinone-3 reverses the inhibition by HpHOQnO and stimulates the electron flow. 7. The different influence of ubiquinone-3 in binding and in inhibition experiments is discussed as a result of redox conditions.
...
PMID:Binding and inhibitory effect of 2-heptyl-4-hydroxyquinoline-N-oxide in the presence of ubiquinone-3 in Saccharomyces cerevisiae. 624 82

1. A mehod for the isolation of a monodisperse ubiquinol-cytochrome c reductase (complex III) from beef heart mitochondria has been developed. The procedure consists of an enzyme solubilization in Triton X-100 followed by hydroxyapatite and gel chromatography. 2. The minimum unit of the isolated complex is composed of 9 polypeptide subunits with Mr of 49000, 47000, 30000, 25000, 12000, 11000 and 6000. It contains 8 mumol of cytochrome b, 4 mumol of cytochrome c1, 7-8 mumol of nonhemne iron, corresponding to 3.5-4 mumol of the Rieske iron-sulfur protein, less than 1.0 mumol of ubiquinone and about 60 mumol of phospholipids, per g of protein. The specific detergent binding amounts to 0.2g of Triton X-100 per g protein. 3. Cytochrome b exhibits an alpha-absorbance maximum at 562 nm. In redox titrations it reveals two half-reduction potentials, i.e. -10 and + 100 mV, at pH 7.0. The absorbance maximum of cytochrome c1 lies at 553 nm and its half-reduction potential amounts to +250 mV. 4. The reductase reveals electron-transferring activity with ubiquinol-1, -2, -3, and -9 as donor and cytochrome c as acceptor. The activity with ubiquinol-9 was analyzed according to the surface dilution scheme developed for the action of phospholipases. The molecular activity amounts to 75 mol of cytochrome c reduced per s at 20%C. 5. A dissociation constant K's of 5.5 mM has been determined for the Tritonsolubilized enzyme: ubiquinol-containing micelle association. In this case the total concentration of ubiquinol plus Triton X-100 has been substituted for the concentration of binding areas on the ubiquinol-containing micelles. This substitution makes the reasonable assumption that the sum of ubiquinol concentration plus Triton X-100 is proportional to the number of available binding areas. 6. A K'm value of 0.025 was found for ubiquinol-9. This is an analog to the Michaelis constant and is expressed as mol fraction of ubiquinol in the ubiquinol-Triton micelle.
...
PMID:Ubiquinol-cytochrome c reductase (EC 1.10.2.2). Isolation in triton X-100 by hydroxyapatite and gel chromatography. Structural and functional properties. 625 May 88

The Rieske iron-sulfur center in the photosynthetic bacterium Rhodopseudomonas sphaeroides appears to be the direct electron donor to ferricytochrome c2, reducing the cytochrome on a submillisecond timescale which is slower than the rapid phase of cytochrome oxidation (t 1/2 3-5 microseconds). The reduction of the ferricytochrome by the Rieske center is inhibited by 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT) but not by antimycin. The slower (102 ms) antimycin-sensitive phase of ferricytochrome c2 reduction, attributed to a specific ubiquinone-10 molecule (Qz), and the associated carotenoid spectral response to membrane potential formation are also inhibited by UHDBT. Since the light-induced oxidation of the Rieske center is only observed in the presence of antimycin, it seems likely that the reduced form of Qz (QzH2) reduces the Rieske Center in an antimycin-sensitive reaction. From the extent of the UHDBT-sensitive ferricytochrome c2 reduction we estimate that there are 0.7 Rieske iron-sulfur centers per reaction center. UHDBT shifts the EPR derivative absorption spectrum of the Rieske center from gy 1.90 to gy 1.89, and shifts the Em,7 from 280 to 350 mV. While this latter shift may account for the subsequent failure of the iron-sulfur center to reduce ferricytochrome c2, it is not clear how this can explain the other effects of the inhibitor, such as the prevention of cytochrome b reduction and the elimination of the uptake of HII(+); these may reflect additional sites of action of the inhibitor.
...
PMID:The role of the Rieske iron-sulfur center as the electron donor to ferricytochrome c2 in Rhodopseudomonas sphaeroides. 625 67

<< Previous 1 2 3 4 5 6 7 8 9 10