Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q16795 (ubiquinone)
 5,455 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Submitochondrial particles from Neurospora strain inl-89601 have been analyzed by electron spin resonance spectroscopy (ESR). Numerous signals due to iron-sulfur proteins are observed at low temperatures. Analysis of these ESR signals at various temperatures allows the assignment of resonances to iron-sulfur centers 1-5 that have been described in other organisms. There are no discrepancies between the signals seen in Neurospora and those described in other organisms and it is likely that Neurospora mitochondria contain the same iron-sulfur centers that are observed elsewhere. 2. NADPH and NADH act to reduce the iron-sulfur centers of respiratory complex I. 3. The drug pyrrolnitrin [3-chloro-4-(2'-nitro-3'-chlorphenyl)pyrrole] is an effective inhibitor of both NADH-supported and succinate-supported electron transport in Neurospora. 4. Analysis of pyrrolnitrin inhibition curves, respiration studies, ESR spectra, and the steady-state level of reduction of cytochrome b in the presence and absence of the drug shows that pyrrolnitrin acts to inhibit electron transport in Neurospora mitochondria at multiple sites in the region between ubiquinone and cytochrome b.
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PMID:Electron spin resonance investigations of mitochondrial electron transport in Neurospora crassa. Characterization of paramagnetic intermediates in a standard strain. 1 65

This paper clarifies the role of cytochrome c in Pseudomonas AM1 by measuring the stoicheiometry of proton translocation driven by respiration of endogenous or added substrates in wild-type bacteria and in a mutant lacking cytochrome c (mutant PCT76). The maximum -->H(+)/O ratio (protons translocated out of the bacteria per atom of oxygen consumed during respiration) was about 4 and, except when respiration was markedly affected, this ratio was similar in mutant and wild-type bacteria. The -->H(+)/O ratios were unaltered when the usual oxidase (cytochrome a(3)) was inhibited by 300mum-KCN and respiration involved the single cytochrome b functioning as an alternative oxidase. Ratios measured in cells respiring endogenous substrate and in cells loaded with malate or 3-hydroxybutyrate suggest that there are two proton-translocating segments operating during the oxidation of NADH. By contrast, during oxidation of formaldehyde or methylamine only one pair of protons is translocated. Proton translocation could not be measured with methanol as substrate, because its oxidation was inhibited (90-95%) by 5mm-KSCN. It is tentatively proposed that the electron-transport chain for NADH oxidation in Pseudomonas AM1 is arranged such that the NADH-ubiquinone oxidoreductase forms one proton-translocating segment and the second segment consists of ubiquinone and cytochromes b and a/a(3). The cytochrome c appears to be essential only for respiration and proton translocation from methanol (and possibly from methylamine); there is no conclusive evidence that cytochrome c ever mediates between cytochromes b and a/a(3) in Pseudomonas AM1.
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PMID:The microbial metabolism of Cl compounds. The stoicheiometry of respiration-driven proton translocation in Pseudomonas AM1 and in a mutant lacking cytochrome c. 2 51

The effect of antimycin on the ubiquinone cytochrome b-c2 (Q b-c2) oxidoreductase of the photosynthetic bacterium Rhodopseudomonas sphaeroides has been studied under controlled oxidation-reduction potential (Eh) conditions by equilibrium measurements and by rapid kinetic analysis of single turnover flash.induced electron and proton translocations. 1. Antimycin shifts the alpha-band of ferro b50 (lambda max 560 nm) by 1 to 2 nm toward the red but has no apparent effect on the equilibrium oxidation-reduction midpoint potential of the cytochrome. 2. This red shift is proportional to the antimycin added until a "titer" of 0.7 +/- 0.1 antimycin per reaction center (RC) is approached. With a similar titer antimycin essentially abolishes the following millisecond reactions activated by saturating single turnover flashes: reduction of ferri c2, oxidation of ferro b, Phase III of the membrane-potential-indicating band shift of endogenous carotenoid pigments, and the uptake of 1 of the 2 protons taken up per electron transferred. Such titrations indicate that the binding (KD approximately 10(-9) m) and mode of inhibition of antimycin are noncooperative and are independent of the membrane's coupling status and of the pH and Eb over the range in which electron transport is operative. 3. In the presence of excess antimycin a partial recovery of ferri c2 reduction is seen when the intensity of the flash is diminished, but only at Eh values such that Z (a special quinone serving as reductant for ferri c2) is reduced but b50 is oxidized before activation. These results are consistent with the following model. Each Q b-c2 oxidoreductase complex includes one antimycin binding site, one b50, and one Z. These complexes and the c2 . RC complexes, present in an 0.7:1 ratio, are to some degree mobile with respect to each other. Ferri b50 can be reduced either via the quinones of the RC or via Z in a reaction also involving c2. The former route is kinetically dominant in the presence of antimycin, but the latter route is the means for "oxidant-induced reduction" and depends on the collisional interaction of the oxidoreductase and c2 . RC complexes. Antimycin interferes with neither of these two routes but does inhibit the oxidation of ferro b50; all the other inhibitory effects are consequent on this.
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PMID:Electron and proton transport in the ubiquinone cytochrome b-c2 oxidoreductase of Rhodopseudomonas sphaeroides. Patterns of binding and inhibition by antimycin. 3 53

The transition of the bacterial culture into the stationary growth phase is accompanied by an appearance of cyanide-resistant respiration. Chloramphenicol inhibits the development of cyanide-resistant respiration. The cyanide-resistant oxidase is localized in the bacterial membrane. Its appearance is not due to the quantitative and qualitative changes of flavins, non-heme iron, ubiquinone and cytochromes of the b and c types, but is accompanied by an increase in the copper content of the membrane preparations. Neither cyanide-sensitive, nor cyanide-resistant chains of the bacterial electron transfer contain cytochromes of the a type. The cyanide-resistant oxidase accepts electrons at the ubiquinone--cytochrome b level of the main respiratory chain. The cyanide-resistant respiration is not accompanied by a formation of hydrogen peroxide. Cytochrome o performs the function of cyanide-sensitive oxidase. The nature of cyanide-resistant oxidase still remains obscure.
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PMID:[Cyanide-resistant respiration of Pseudomonas aeruginosa bacteria]. 10 78

1. Respiration of chemotrophically and phototrophically grown Rhodospirillum rubrum is inhibited by 2-hydroxydiphenyl. 2. Membrane-bound NADH oxidase and NADH: cytochrome c reductase are inhibited also. The inhibitor constant for both reactions (Ki) is 0.075 plus or minus 0.012 mM. NADH dehydrogenase is not inhibited significantly. 3. The inhibition of succinate:cytochrome c reductase is associated for chemotrophic membranes with Ki equals 0.22 plus or minus 0.03 mM and for phototrophic membranes with Ki equals 0.49 plus or minus 0.09 mM. Succinate dehydrogenase is not affected by 2-hydroxydiphenyl. 4. Cytochrome oxidase is inhibited only slightly. 5. While NADH-dependent reactions in both phototrophic and chemotrophic membranes are inhibited maximally more than 95 percent, succinate-dependent reactions can be inhibited more than 95 percent only in chemotrophic membranes. In phototrophic membranes the maximum inhibition of succinate-dependent reactions is about 70 percent. 6. The type of inhibition in both cases 2 and 3 is non-competitive. 7. While the reduction of b-type cytochrome is inhibited by 2-hydroxydiphenyl, the degree of ubiquinone reduction is not influenced. The data suggest that the site of inhibition is localized between ubiquinone and cytochrome b. 8. Implications of these data for the respiratory electron transport system in R. rubrum are discussed.
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PMID:Separation of respiratory reactions in Rhodospirillum rubrum: inhibition studies with 2-hydroxydiphenyl. 16 37

Production of superoxide radical during oxidation of dihydroorotate in rat liver mitochondria was not affected by antimycin A, thenoyltrifluoroacetone, or added ubiquinone but was inhibited by orotate, a product inhibitor of dihydroorotate dehydrogenase. It appears likely that superoxide is generated at the primary dehydrogenase. Dihydroorotate dehydrogenase differs from succinate dehydrogenase both in its utilization of ubiquinone and in the mechanism of cytochrome b reduction. Thenoyltrifluoroacetone completely inhibits fumarate synthesis and reduction of cytochrome b by succinate. Formation of orotate is only partially inhibited by thenolytrifluoroacetone and the inhibitor does not prevent reduction of cytochrome b by dihydroorotate. It is proposed that several pathways exist for linkage of the primary dihydrorotate dehydrogenase with the electron transport chain. One route involves electron transfer from ubiquinone to cytochrome c and is inhibited by thenoyltrifluoroacetone. A second route bypasses ubiquinone and is inhibited by antimycin A. A third pathway utilizes both ubiquinone and cytochrome b and is partiayly inhibited by either thenoyltrifluoroacetone or antimycin A.
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PMID:Superoxide production and electron transport in mitochondrial oxidation of dihydroorotic acid. 16 96

The effect of antimycin on (i) the respiratory activity of the KCN-insensitive pathway of mitochondria of Neurospora grown on chloramphenicol (chloramphenicol-grown) with durohydroquinone and succinate or NADH as substrate, (ii) the electron transfer from the b-type cytochromes to ubiquinone with durohydroquinone as electron donor as well as (iii) the electron transfer from the b-type cytochromes to duroquinone with succinate as electron donor in chloramphenicol-grown Neurospora and beef heart submitochondrial particles was studied. All experiments were performed in the uncoupled state. 1. The respiratory chain of chloramphenicol-grown Neurospora mitochondria branches at ubiquinone into two pathways. Besides the cytochrome oxidase-dependent pathway, a KCN-insensitive branch equiped with a salicylhydroxamate-sensitive oxidase exists. Durohydroquinone, succinate or NADH are oxidized via both pathways. The durohydroquinone oxidation via the KCN-insensitive pathway is inhibited by antimycin, wheras the succinate or NADH oxidation is not. The titer for ful inhibition is one mol antimycin per mol cytochrome b-563 or cytochrome b-557. 2. The electron transfer from durohydroquinone to ubiquinone, which takes place in the KCN-inhibited state, does not occur in the antimycin-inhibited state. 3. The reduction of duroquinone by succinate in the presence of KCN is inhibited by antimycin. The titer for full inhibition is one mol antimycin per mol cytochrome b-566 or cytochrome b-562 for beef heart (or cytochrome b-563 or cytochrome b-557 for Neurospora). 4. When electron transfer from the b-type cytochromes to cytochrome C1, ubiquinone and duroquinone is inhibited by antimycin, the hemes of cytochrome b-566 and cytochrome b-562 (or cytochrome b-563 and cytochrome b-557) are in the reduced state. 5. The experimental results suggest that the two b-type cytochromes form a binary complex the electron transferring activity of which is inhibited by antimycin, the titer for full inhibition being one mol of antimycin per mol of complex. The electron transfer from the b-type cytochromes to ubiquinone is inhibited in a non-linear fashion.
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PMID:Inhibition of electron transfer from ferrocytochrome b to ubiquinone, cytochrome c1 and duroquinone by antimycin. 16 67

In Rhodopseudomonas sphaeroides, following a single-turnover flash of light, cytochrome c2 is oxidized by reaction center bacteriochlorophyll, and a cytochrome b is reduced by the primary electron acceptor, probably via ubiquinone. In this report we show that, in the uncoupled state, the rate of re-oxidation of the cytochrome b is identical to the rate of reduction of the cytochrome c2, a kinetic completion of the cyclic photosynthetic electron transport system.
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PMID:A kinetic completion of the cyclic photosynthetic electron pathway of Rhodopseudomonas sphaeroides: cytochrome b-cytochrome c2 oxidation-reduction. 16 71

Various respiratory electron transport activities of Rhodopseudomonas capsulata were studied in membrane fragments prepared from photosynthetically grown cells of a parental strain and two terminal oxidase-defective mutant strains. The NADH and succinate oxidase activities of the mutant having a functional N,N,N1,N1-tetramethyl-p-phenylenediamine oxidase, M6, were consideraly more sensitive to inhibition by either antimycin A or cyanide than the corresponding activities of the mutant lacking a functional N,N,N1,N1-tetramethyl-p-phenylenediamine oxidase, M7. The parental strain, Z-1, but not the mutants, showed biphasic inhibitory responses of NADH and succinate oxidase activities with either antimycin A or cyanide. In certain reactions no differences in inhibitor susceptibility were found among the strains tested, implying that the pathways involved were unaffected in the mutants. In this category were the actions of rotenone on NADH oxidase, antimycin A on cytochrome c reductase and, in M6 and Z-1, cyanide on N,N,N'N'-tetramethyl-p-phenylenediamine oxidase. These results suggest that the respiratory chain of the parental strain branches at the ubiquinone-cytochrome b region into two pathways, each branch goes to a distinct terminal oxidase, and either may be blocked independently by genetic mutation.
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PMID:The branched respiratory system of photosynthetically grown Rhodopseudomonas capsulata. 17 46

Tridemorph (N-tridecyl-2,6-dimethylmorpholine) inhibits both the NADH-oxidase and the succinate-cytochrome c oxydoreductase system of non-phosphorylating electron transfer particles from beef heart. The concentration required for half-inhibition amounted to 3,4 muM and 24 muM respectively. Two different sites of action in the respiratory chain could be localized by means of difference spectroscopy and measurements of enzymic activities in various partial systems. The inhibition of the NADH-ubiquinone oxydoreductase activity as well as the suppression of the NADH-induced reduction of all cytochromes on the one hand and the insensitivity of the NADH-ferricyanide oxydoreductase system on the other argue in favour of a site of action similar to rotenone. The partial suppression of the succinate-induced reduction of cytochrome b with simultaneous complete inhibition of the reduction of the other cytochromes indicate an additional site of action analogous to antimycin A. Both inhibitory actions appeared instantaneously after the addition of tridemorph and were counteracted by serum albumin. Furthermore, tridemorph inhibited the oxydation of external ferrocytochrome c but not that of ascorbate/tetra-methyl-p-phenylene-diamine-HCI (TMPID) showing that it is not a true inhibitor of the cytochrome oxidase. The TMPD-induced bypass of the succinate oxidation was inhibited as well. The possible role of the inhibition of the main pathway of the respiratory chain for the fungicidal action of tridemorph is discussed.
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PMID:[The systemic fungicide tridermorph as an inhibitor of the respiratory chain of electron transfer particles from beef heart mitochondria]. 18 65


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