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

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Query: EC:1.6.5.3 (complex I)
8,901 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Oxidation of exogenous NADH in mitochondria isolated from wild type and mi-1 mutant of Neurospora crassa decreases rapidly in vitro. In mi-1 mutant mitochondria the inactivation concerns the alternate pathway of oxidation whereas in the wild type it involves an unknown component of the respiratory chain. The activity of the primary NADH dehydrogenase is constant within the time of the experiments (2-4 h). NADH oxidase is not inactivated if oxygen is removed from the incubation medium by nitrogen bubbling. Succinate oxidase does not show any remarkable changes in activity within 2-3 h. In fresh mitochondria of the mi-1 mutant reduced ubiquinone is completely reoxidized by cytochrome oxidase but only 80% reoxidized by the alternate oxidase. In aged mitochondria of the mi-1 mutant in the presence of cyanide, ubiquinone is reduced to the level characteristic for fresh mitochondria in which respiration is completely inhibited by cyanide plus salicylhydroxamic acid. In these mitochondria the reoxidation of the reduced ubiquinone proceeds only via the cytochrome pathway. It is supposed that a labile component(s) of the respiratory chain present in the mi-1 mutant and the wild type mitochondria may, in mi-1 mutant, act as an alternate oxidase.
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PMID:Disappearance of the cyanide-insensitive pathway of oxidation in mitochondria of MI-1 mutant of Neurospora crassa in vitro. 20 34

In Rhodopseudomonas sphaeroides chromatophores there are 25 +/- 3 ubiquinone (Q) molecules/reaction center protein. They comprise several thermodynamically and functionally different ubiquinone complements. There are approx. 19 ubiquinones (Em7 = 90 mV) in the main ubiquinone complement which, within experimental resolution, appears thermodynamically homogenous and follows the redox reaction Q + 2e + 2H+ in equilibrium with QH2 from pH 5--9. A method which takes advantage of the 2H+ bound/molecule of Q reduced is described for measuring the time course of light-activated reaction center-driven reduction and oxidation of the 19 Q complement. No stable semiquinones were detected in the constitutents of the 19 Q complement. There are approx. 6 ubiquinones of lower Em which are currently unaccounted for, although one or possibly two of these can be assigned to the quinones of the reaction center protein. The remainder may be associated with the NADH-ubiquinone oxidoreductase.
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PMID:Ubiquinone in Rhodopseudomonas sphaeroides. Some thermodynamic properties. 22 Oct 12

Oxidation factor, a protein required for electron transfer from succinate to cytochrome c in the mitochondrial respiratory chain, has been purified from isolated succinate . cytochrome c reductase complex. Purification of the protein has been followed by a reconstitution assay in which restoration of ubiquinol . cytochrome c reductase activity is proportional to the amount of oxidation factor added back to depleted reductase complex. The purified protein is a homogeneous polypeptide on acrylamide gel electrophoresis in sodium dodecyl sulfate and migrates with an apparent Mr = 24,500. Purified oxidation factor restores succinate . cytochrome c reductase and ubiquinol . cytochrome c reductase activities to depleted reductase complex. It is not required for succinate dehydrogenase nor for succinate . ubiquinone reductase activities of the reconstituted reductase complex. Oxidation factor co-electrophoreses with the iron-sulfur protein polypeptide of ubiquinol . cytochrome c reductase complex. The purified protein contains 56 nmol of nonheme iron and 36 nmol of acid-labile sulfide/mg of protein and possesses an EPR spectrum with the characteristic "g = 1.90" signal identical to that of the iron-sulfur protein of the cytochrome b . c1 complex. In addition, the optimal conditions for extraction of oxidation factor, including reduction with hydrosulfite and treatment of the b . c1 complex with antimycin, are identical to those which facilitate extraction of the iron-sulfur protein from the b . c1 complex. These results indicate that oxidation factor is a reconstitutively active form of the iron-sulfur protein of the cytochrome b . c1 complex first discovered by Rieske and co-workers (Rieske, J.S., Maclennan, D.H., and Coleman, R. (1964) Biochem. Biophys. Res. Commun. 15, 338-344) and thus demonstrate that this iron-sulfur protein is required for electron transfer from ubiquinol to cytochrome c in the mitochondrial respiratory chain.
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PMID:Purification of a reconstitutively active iron-sulfur protein (oxidation factor) from succinate . cytochrome c reductase complex of bovine heart mitochondria. 22 62

The enzymic activities NADH-ubiquinone reductase, succinate-ubiquinone reductase and ubiquinol oxidase were evaluated in beef heart mitochondria in presence of short ubiquinone homologs. Preliminar data obtained indicate that short chain homologs, less lipophilic than natural ubiquinone do not reach the reoxidation site in absence of endogenous ubiquinone.
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PMID:Effect of endogenous ubiquinone on the reduction and oxidation of short exogenous ubiquinone homologs in beef heart mitochondria. 57 63

The reduction of duroquinone (DQ) and 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinone (DB) by NADH and ethanol was investigated in intact yeast mitochondria with good respiratory control ratios. In these mitochondria, exogenous NADH is oxidized by the NADH dehydrogenase localized on the outer surface of the inner membrane, whereas the NADH produced by ethanol oxidation in the mitochondrial matrix is oxidized by the NADH dehydrogenase localized on the inner surface of the inner membrane. The reduction of DQ by ethanol was inhibited 86% by myxothiazol; however, the reduction of DQ by NADH was inhibited 18% by myxothiazol, suggesting that protein-protein interactions between the internal (but not the external) NADH: ubiquinone oxidoreductase and ubiquinol:cytochrome c oxidoreductase (the cytochrome bc1 complex) are involved in the reduction of DQ by NADH. The reduction of DQ and DB by NADH and ethanol was also investigated in mutants of yeast lacking cytochrome b, the iron-sulfur protein, and ubiquinone. The reduction of both quinone analogues by exogenous NADH was reduced to levels that were 10 to 20% of those observed in wild-type mitochondria; however, the rate of their reduction by ethanol in the mutants was equal to or greater than that observed in the wild-type mitochondria. Furthermore, the reduction of DQ in the cytochrome b and iron-sulfur protein lacking mitochondria was myxothiazol sensitive, suggesting that neither of these proteins is an essential binding site for myxothiazol. The mitochondria from the three mutants also contained significant amounts of antimycin- and myxothiazol-insensitive NADH:cytochrome c reductase activity, but had no detectable succinate:cytochrome c reductase activity. These results suggest that the mutants lacking a functional cytochrome bc1 complex have adapted to oxidize NADH.
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PMID:Direct interaction between the internal NADH: ubiquinone oxidoreductase and ubiquinol:cytochrome c oxidoreductase in the reduction of exogenous quinones by yeast mitochondria. 130 74

Deletion of QCR9, the nuclear gene encoding subunit 9 of the mitochondrial cytochrome bc1 complex in Saccharomyces cerevisiae, results in inactivation of the bc1 complex and inability of the yeast to grow on non-fermentable carbon sources. The loss of bc1 complex activity is due to loss of electron transfer activity at the ubiquinol oxidase site (center P) in the complex. Electron transfer at the ubiquinone reductase site (center N), is unaffected by the loss of subunit 9, but the extent of cytochrome b reduction is diminished. This is the first instance in which a supernumerary polypeptide, lacking a redox prosthetic group, has been shown to be required for an electron transfer reaction within the cytochrome bc1 complex.
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PMID:Deletion of subunit 9 of the Saccharomyces cerevisiae cytochrome bc1 complex specifically impairs electron transfer at the ubiquinol oxidase site (center P) in the bc1 complex. 133 81

A small polypeptide subunit of the NADH:ubiquinone reductase (complex I) from Neurospora crassa has been identified by photoaffinity labeling to participate in the binding of ubiquinone [Heinrich, H., & Werner, S. (1992) Biochemistry (preceding paper in this issue)]. This polypeptide is further characterized by its primary structure and by an assessment of its localization within complex I. A lambda gt11 cDNA expression library was screened using a specific antibody directed against this individual subunit of complex I. Two groups of clones, coding for polypeptide subunits of the appropriate apparent molecular weight, were isolated. One group was shown to contain the relevant recombinants. The derived amino acid sequence for the 9.5-kDa ubiquinone-binding polypeptide shows a similarity with a putative ubiquinol-binding subunit (also a 9.5-kDa polypeptide) from complex III of bovine heart [Usui, S., Yu, L., & Tu, C.-A. (1990) Biochemistry 29, 4618-4626]. The polypeptide has a hydrophobic stretch of a sufficient length to span the membrane. It resists against extraction with NaBr or Na2CO3, and therefore probably is buried in the so-called hydrophobic membrane portion of complex I. This nuclearly-encoded subunit lacks a typical cleavable presequence and is imported into isolated mitochondria by a membrane potential-dependent process.
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PMID:Characterization of the 9.5-kDa ubiquinone-binding protein of NADH:ubiquinone oxidoreductase (complex I) from Neurospora crassa. 144 79

The in vitro toxicity of multiple hydrophobic compounds was the focus of this study. A mitochondrial respiratory assay, sensitive to perturbations caused by hydrophobic chemicals, was utilized to measure the effects of individual aromatic hydrocarbon pollutants and their mixtures on mitochondrial respiratory function. Benzene, naphthalene, acenaphthene, and 1-chloronaphthalene, common industrial solvents shown to interact additively in vivo, were evaluated using this in vitro assay system. Mitochondrial respiration was inhibited 50% (EC50) by 525 ppm (6.7 mM) benzene, 15 ppm (117 microM) naphthalene, 3.9 ppm (25.5 microM) acenaphthene, or 3.8 ppm (23.4 microM) 1-chloronaphthalene. NADH:O2 oxidoreductase (NADH-->O2), NADH:ubiquinone oxidoreductase, and ubiquinol:O2 oxidoreductase activities were inhibited by all four compounds, whereas succinate:O2 oxidoreductase, cytochrome c oxidase, and duroquinol:O2 oxidoreductase activities were not inhibited. Inhibition of mitochondrial respiration occurred at the level of ubiquinone (coenzyme Q10) for all four aromatic hydrocarbons. The ultraviolet absorbance spectrum of isolated Q10 was also altered by naphthalene, acenaphthene, or 1-chloronaphthalene, suggesting a specific interaction between that component of the respiratory chain and these aromatic hydrocarbons. Inhibition by a mixture of 2, 3, or 4 of the compounds tested was additive, reflecting a summation effect of each compound present in the mixture. This additive nature is consistent with previously reported effects of these compounds in vivo and with compounds having similar modes of action. The similar mode of action in vitro is a specific interaction with coenzyme Q10, not a generalized membrane perturbation as speculated to occur in vivo, and is the likely mechanism for the observed additive toxicity.
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PMID:Additive effects and potential inhibitory mechanism of some common aromatic pollutants on in vitro mitochondrial respiration. 147 93

Citrate is fermented by Klebsiella pneumoniae to 2 acetate, 0.5 formate and 1.2 CO2. The formation of less than 1 formate and greater than 1 CO2 per citrate can be accounted for by the oxidation of formate to CO2 in order to provide reducing equivalents for the assimilation of citrate into cell carbon. A membrane-bound electron transport chain is apparently involved in NADH synthesis by these cells. The electrons from formate oxidation to CO2 are used to reduce ubiquinone to ubiquinol by membrane-bound formate dehydrogenase and ubiquinol further delivers its electrons to NAD+, if this endergonic reaction is powered by delta mu Na+. The endogenous NADH level of K. pneumoniae cells thus increased in the presence of formate in response to a delta pNa+ greater than -100 mV. NADH formation was completely abolished in the presence of oxygen or after addition of hydroxyquinoline-N-oxide, a specific inhibitor of the Na(+)-translocating NADH:ubiquinone oxidoreductase. The increase of endogenous NADH was dependent on the delta pNa+ applied to the cells. Inverted membrane vesicles of K. pneumoniae catalysed the reduction of NAD+ to NADH with formate as electron donor after application of delta mu Na+ of about 120 mV consisting of delta pNa+ of 60 mV and delta psi of the same magnitude. Neither the delta pNa+ nor the delta psi of this size alone was sufficient to drive the endergonic reaction. Strictly anaerobic conditions were required for NADH formation and hydroxyquinoline-N-oxide completely inactivated the reaction.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:NADH formation by Na(+)-coupled reversed electron transfer in Klebsiella pneumoniae. 150 43

It is proved by using the Dixon plot and the Lineweaver-Burk plot that thenoyltrifluoroacetone (TTFA) has two inhibitive sites affecting the reduction of ubiquinone catalyzed by succinate-ubiquinone reductase. The high affinity site (inhibited at the concentration of thenoyltrifluoroacetone less than 20 mumol/L) shows noncompetitive with substrate Q2, while the low affinity site (inhibited at the concentration of TTFA over 20 mumol/L) shows competitive. It is suggested that both the reducing steps of Q----QH-. and QH-.----QH2 are inhibited by thenoyltrifluoroacetone.
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PMID:Two-site property of thenoyltrifluoroacetone inhibiting succinate-ubiquinone reductase. 158 Oct


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