UNIPROT:Q16795 - FACTA Search

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

We report here some unusual properties of ubiquinol: cytochrome c reductase of eel and other fish mitochondria. The turnover rate of the reductase is clearly higher than in mammalian mitochondria and the binding constant for ubiquinone seems to be larger than in other vertebrates. Additionally, the reductase activity of fish mitochondria is resistant to some powerful inhibitors that bind to cytochrome b, in particular to funiculosin. After sequencing most of the gene of eel cytochrome b and comparing the deduced amino acid sequence with that of other fish and animals, we hypothesize that the decreased binding of funiculosin could be due to a few amino acid replacements in the third and fourth transmembrane helix of the protein. In particular, the presence of methionine instead of alanine at position 125 seems to be largely responsible for the strong resistance to funiculosin and also to the partial resistance to myxothiazol in all fish mitochondria. Correlations between some residue substitutions in cytochrome b and the different effects of funiculosin in different species are also considered.
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PMID:Cytochrome b of fish mitochondria is strongly resistant to funiculosin, a powerful inhibitor of respiration. 131 3

The small molecular mass ubiquinone-binding protein (QPc-9.5 kDa) was purified to homogeneity from 3-azido-2-methyl-5-methoxy-6-(3,7-dimethyl[3H]octyl)-1,4-benzoquinol+ ++- labeled bovine heart mitochondrial ubiquinol-cytochrome c reductase. The N-terminal amino acid sequence of the isolated protein is Gly-Arg-Gln-Phe-Gly-His-Leu-Thr-Arg-Val-Arg-His-, which is identical with that of a Mr = 9500 protein in the reductase [Borchart et al. (1986) FEBS Lett. 200, 81-86]. A ubiquinone-binding peptide was prepared from [3H]azidoubiquinol-labeled QPc-9.5 kDa protein by trypsin digestion followed by HPLC separation. The partial N-terminal amino acid sequence of this peptide, Val-Ala-Pro-Pro-Phe-Val-Ala-Phe-Tyr-Leu-, corresponds to amino acid residues 48-57 in the reported Mr = 9500 protein. According to the proposed structural model for the Mr = 9500 protein, the azido-Q-labeled peptide is located in the membrane on the matrix side. These results confirm our previous assessment that the Mr = 13,400 subunit is not the small molecular weight Q-binding protein. Purified antibodies against QPc-9.5 kDa have a high titer with isolated QPc-9.5 kDa protein and complexes that contain it. Although antibodies against QPc-9.5 kDa do not inhibit intact succinate- and ubiquinol-cytochrome c reductases, a decrease of 85% and 20% in restoration of succinate- and ubiquinol-cytochrome c reductases, respectively, is observed when delipidated succinate- or ubiquinol-cytochrome reductases are incubated with antibodies prior to reconstitution with ubiquinone and phospholipid, indicating that epitopes at the catalytic site of QPc-9.5 kDa are buried in the phospholipid environment.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The small molecular mass ubiquinone-binding protein (QPc-9.5 kDa) in mitochondrial ubiquinol-cytochrome c reductase: isolation, ubiquinone-binding domain, and immunoinhibition. 216 42

Herbicides of the triazine class block electron transfer in the photosynthetic reaction centers of purple bacteria and PSII of higher plants. They are thought to act by competing with one of the electron acceptors, the secondary quinone, QB, for its binding site. Several mutants of the purple bacterium Rhodopseudomonas viridis resistant to terbutryn [2-(methylthio)-4-(ethylamino)-6-(tert-butylamino)-s-triazine] have been isolated by their ability to grow photosynthetically in the presence of the herbicide. Sequence analysis of the genes coding for the L and M subunits of the reaction center showed that four different mutants were obtained, two of them being double mutated: T1 (SerL223----Ala and ArgL217----His), T3 (PheL216----Ser and ValM263----Phe), T4 (TyrL222----Phe), and T6 (PheL216----Ser). The residues L223 and L216 are involved in binding of QB, whereas L217 and L222 are not. M263 is part of the binding pocket of the primary quinone, QA. The affinity of the reaction centers for terbutryn and the electron transfer inhibitor o-phenanthroline, determined via the biphasic charge recombination after one flash, is decreased for all mutants. The affinity for ubiquinone 9 is also decreased, except in T1. Characterization by EPR spectroscopy showed that the QB.-Fe2+ signal of T4, having a g = 1.93 peak, is different from the signals obtained with the wild type and the other mutants but very similar to those of Rhodospirillum rubrum and PSII. The results obtained by the combination of these different techniques are discussed with respect to the three-dimensional structure of the wild type and the mode of binding of ubiquinone, terbutryn, and o-phenanthroline as determined by X-ray structure analysis.
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PMID:Characterization of four herbicide-resistant mutants of Rhodopseudomonas viridis by genetic analysis, electron paramagnetic resonance, and optical spectroscopy. 255 55

The pattern of incorporation of radioactivity from [1-14C]acetate and [2-14C]acetate into the polyprenyl side-chain of ubiquinones in bacteria (Azotobacter vinelandii, Pseudomonas sesami, Escherichia coli and Rhodopseudomonas capsulata) was studied. For this purpose, a new degradation method involving a modified Barbier-Wieland reaction of laevulinic acid was developed, and used along with the iodoform reaction. Both C-1 and C-2 of acetate were incorporated exclusively into C-2 of laevulinic acid suggesting that the well-known pathway through acetoacetyl-CoA ('acetoacetate pathway') was not operative in these bacteria. An alternative pathway ('acetolactate pathway'), starting with pyruvate and acetaldehyde as the distal precursors, and utilizing the reactions of leucine and valine metabolism, was postulated. It was also postulated that C-1 of acetate is incorporated not directly, but after oxidation to CO2. The pattern of incorporation of radioactivity from [U-14C]valine, [U-14C]alanine and NaH14CO3 into the side-chain of ubiquinone of R. capsulata was in agreement with the operation of the 'acetolactate pathway'.
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PMID:An alternative pathway for the biosynthesis of isoprenoid compounds in bacteria. 627 17

Electron transport in continuous light has been investigated in chromatophores of Rhodopseudomonas capsulata. Ala pho+, depleted in ubiquinone-10 and subsequently reconstituted with various ubiquinone homologs and analogs. In addition the restoration of electron transport in depleted chromatophores by the artificial redox compounds N-methylphenazonium methosulfate and N,N,N',N'-tetramethyl-p-phenylenediamine was studied. The following pattern of activities was obtained: (1) Reconstitution of cyclic photophosphorylation with ubiquinone-10 was saturated at about 40 ubiquinone molecules per reaction center. (2) Reconstitution by ubiquinone homologs was dependent on the length of the isoprenoid side chain and the amount of residual ubiquinone in the extracted chromatophores. If two or more molecules of ubiquinone-10 per reaction center were retained, all homologs with a side chain longer than two isoprene units were as active as ubiquinone-10 in reconstitution, and the double bonds in the side chain were not required. If less than two molecules per reaction center remained, an unsaturated side chain longer than five units was necessary for full activity. Plastoquinone, alpha-tocopherol, and naphthoquinones of the vitamin K series were relatively inactive in both cases. (3) All ubiquinone homologs, also ubiquinone-1 and -2, could be reduced equally well by the photosynthetic reaction center, as measured by light-induced proton binding in the presence of antimycin A and uncoupler. Plastoquinone was found to be a poor electron acceptor. (4) Photophosphorylation could be reconstituted by N-methylphenazonium methosulfate as well as by N,N,N',N'-tetramethyl-p-phenylenediamine in an antimycin-insensitive way, if more than two ubiquinones per reaction center remained. These compounds were active also in more extensively extracted particles reconstituted with ubiquinone-1, which itself was inactive.
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PMID:Structural requirements of quinone coenzymes for endogenous and dye-mediated coupled electron transport in bacterial photosynthesis. 721 45

The DNA sequence of the regulatory region and the structural gene, nrfA, for cytochrome c552 of Escherichia coli K-12 have been reported. We have now established that nrfA is the first gene in a seven-gene operon, designated the nrf operon, at least five of which are essential for formate-dependent nitrite reduction to ammonia. This operon terminates just upstream of the previously sequenced gltP gene encoding a sodium-independent, glutamate and aspartate transporter. Expression of lac fused to nrfA, nrfE or nrfG is regulated by oxygen repression, FNR-dependent anaerobic induction, nitrite induction and nitrate repression during anaerobic growth, exactly as previously reported for the nrfA promoter. In contrast, expression of the gltP-lac fusion was FNR-independent. The open reading frame immediately downstream of nrfA encodes NrfB, a hydrophilic, penta-haem cytochrome c with an M(r) of 20,714. The structure of the N-terminal region is typical of a signal peptide for a periplasmic protein: cleavage at the putative signal peptide cleavage site, Ala-26, would result in a periplasmic cytochrome with a molecular mass of 18 kDa. The NrfC polypeptide, M(r) 24,567, contains 16 cysteine residues arranged in four clusters typical of the CooF super-family of non-haem iron-sulphur proteins. The NrfD sequence predicts a 318-residue hydrophobic protein with a distribution of acidic and basic amino acids which suggests that NrfD is an integral transmembrane protein with loops in both the periplasm and the cytoplasm. Proteins most similar to NrfD include the PsrC subunit of polysulphide reductase from Wolinella, but, as seven of the 10 most similar proteins are NADH-ubiquinone oxidoreductases, we propose that NrfD participates in the transfer of electrons from the quinone pool into the terminal components of the Nrf pathway. NrfE, M(r) 60,851, is predicted to be another hydrophobic, integral membrane protein homologous to the CdI1 protein of Rhodobacter capsulatus, which has been implicated in the assembly of periplasmic c-type cytochromes. The sequence of the 127 residue NrfF polypeptide, M(r) 14,522, is strikingly similar to the CcI2 protein of R. capsulatus, especially in the putative haem-binding motif, RCPQCQNQN.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:A seven-gene operon essential for formate-dependent nitrite reduction to ammonia by enteric bacteria. 805 35

Reaction centers from the purple bacterium Rhodobacter (Rb.) capsulatus and from two mutants ThrL226-->Ala and IleL229-->Ser, modified in the binding protein pocket of the secondary quinone acceptor (QB), have been studied by flash-induced absorbance spectroscopy. In ThrL226-->Ala, the binding affinities for endogenous QB (ubiquinone 10) and UQ6 are found to be two to three times as high as the wild type. In contrast, in IleL229-->Ser, the binding affinity for UQ6 is decreased about three times compared to the wild type. In ThrL226-->Ala, a markedly increased sensitivity (approximately 30 times) to o-phenanthroline is observed. In Rhodopseudomonas viridis, where Ala is naturally in position L226, the sensitivity to o-phenanthroline is close to that observed in ThrL226-->Ala. We propose that the presence of Ala in position L226 is responsible for the high sensitivity to that inhibitor. The pH dependencies of the rate constants of P+QB- (kBP) charge recombination kinetics (P is a dimer of bacteriochlorophyll, and QB is the secondary quinone electron acceptor) show destabilization of QB- in ThrL226-->Ala and IleL229-->Ser, compared to the wild type. At low pH, similar apparent pK values of protonation of amino acids around QB- are measured in the wild type and the mutants. In contrast to Rb. sphaeroides, in the wild type Rb. capsulatus, kBP substantially increases in the pH range 7-10. This may reflect some differences in the respective structures of both strains or, alternatively, may be due to deprotonation of TyrL 215 in Rb. capsulatus. At pH 7, measurements of the rate constant of QA to QB electron transfer reveal a threefold greater rate in the reaction centers from wild type Rb. capsulatus (65 +/- 1 0 ps)-1 compared to Rb. sphaeroides.We suggest that this may arise from a 0.7-A smaller distance between the quinones in the former strain. Our spectroscopic data on the wild type Rb. capsulatus reaction center suggest the existence of notable differences with the Rb. sphaeroides reaction center structure.
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PMID:Study of wild type and genetically modified reaction centers from Rhodobacter capsulatus: structural comparison with Rhodopseudomonas viridis and Rhodobacter sphaeroides. 821 94

Escherichia coli fumarate reductase (FRD) is a four-subunit enzyme that catalyzes the terminal step in anaerobic respiration to fumarate. The hydrophobic FrdC and FrdD subunits anchor the FrdA and FrdB catalytic subunits to the inner surface of the cytoplasmic membrane and are required for the enzyme to interact with quinones. Thirty-five single-site mutations were constructed in the FrdC and FrdD polypeptides by site-directed mutagenesis. Each mutant enzyme was characterized for its ability to catalyze quinone oxidation and reduction and to support growth of E. coli DW35 (delta frdABCD sdhC::kan) under selective conditions requiring functional enzyme. Replacement of FrdCE29 with Asp, Leu, Lys, or Phe had a deleterious effect both on quinol oxidase and quinone reductase activities. Substitution of FrdCH82 with Arg, Leu, Tyr, or Glu also decreased menaquinol oxidase activity, but had variable effects on the reverse reaction, the reduction of ubiquinone. Data are presented to support the hypothesis that the positive charge at FrdCH82 is required for stabilization of the quinone radical intermediate and the negative charge at FrdCE29 for deprotonation of menaquinol. Other critical amino acids identified in FrdC included Ala-32, Phe-38, Trp-86, Phe-87, and in FrdD residues Phe-57, Gln-59, Ser-60, and His-80. The established roles of such residues in the QA and QB sites of the photosynthetic reaction center would suggest a similar type of structure operative in the FRD complex. In such a model, Glu-29, Ala-32, His-82, Trp-86 of FrdC and His-80 of FrdD are considered participants in a QB-type site, and FrdD Phe-57, Gln-59, and Ser-60 components in an apolar QA-type site.
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PMID:Escherichia coli fumarate reductase frdC and frdD mutants. Identification of amino acid residues involved in catalytic activity with quinones. 841 59

In the reaction center of purple photosynthetic bacteria, the reducing equivalents produced by primary charge separation are exported via an ubiquinone molecule working as a two-electron shuttle. This loosely-bound quinone, called QB, accepts in successive flashes two electrons from the tightly bound primary quinone acceptor QA, along with two protons from the external medium. The surrounding protein plays an important role in stabilizing the semiquinone anion and in providing a pathway for protons from the cytoplasmic phase to QB. Herbicides of the triazine type compete with QB for the binding pocket and their binding is controlled by nearby amino acid residues. We have studied the kinetics of the first and second electron transfer from QA to QB in two herbicide-resistant mutants from Rhodopseudomonas viridis, T1 (ArgL217-->His,Ser L223-->Ala) and MAV5 (Arg L217-->His, Val L220-->Leu), in order to determine whether these residues are involved in proton transfer to the reduced QB. The main effect of the mutant T1 was a drastic (600-fold at pH 7) decrease in the rate of the second electron transfer to QB compared to the wild type. In contrast, the rate of the second electron transfer in the mutant MAV5 was decreased only slightly (10-fold) in the pH range from 7 to 11. We attribute the inhibition of the second electron transfer in the Ser L223-->Ala mutation to an essential role of Ser L223 in the donation of the first proton to the reduced QB.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Evidence that serine L223 is involved in the proton transfer pathway to QB in the photosynthetic reaction center of Rhodopseudomonas viridis. 844 55

Inhibitors of HMG-CoA reductase are new safe and effective cholesterol-lowering agents. Elevation of alanine-amino transferase (ALT) and aspartate-amino transferase (AST) has been described in a few cases and a myopathy with elevation of creatinine kinase (CK) has been reported rarely. The inhibition of HMG-CoA reductase affects also the biosynthesis of ubiquinone (CoQ10). We studied two groups of five healthy volunteers treated with 20 mg/day of pravastatin (Squibb, Italy) or simvastatin (MSD) for a month. Then we treated 30 hypercholesterolemic patients in a double-blind controlled study with pravastatin, simvastatin (20 mg/day), or placebo for 3 months. At the beginning, and 3 months thereafter we measured plasma total cholesterol, CoQ10, ALT, AST, CK, and other parameters (urea, creatinine, uric acid, total bilirubin, gamma GT, total protein). Significant changes in the healthy volunteer group were detected for total cholesterol and CoQ10 levels, which underwent about a 40% reduction after the treatment. The same extent of reduction, compared with placebo was measured in hypercholesterolemic patients treated with pravastatin or simvastatin. Our data show that the treatment with HMG-CoA reductase inhibitors lowers both total cholesterol and CoQ10 plasma levels in normal volunteers and in hypercholesterolemic patients. CoQ10 is essential for the production of energy and also has antioxidative properties. A diminution of CoQ10 availability may be the cause of membrane alteration with consequent cellular damage.
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PMID:Evidence of plasma CoQ10-lowering effect by HMG-CoA reductase inhibitors: a double-blind, placebo-controlled study. 846 36

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