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)

The relative rates of reduction of several spin-labeled molecules that partition differently across the hy-drophobic-interface of inner membranes from rat liver mitochondria were investigated. Spin labels localized either deep in the hydrophobic region or in the aqueous phase are only slowly reduced; however a spin-labeled analogue of the cationic detergent cetyltrimethylammonium bromide that partitions at the interface is rapidly reduced by coupled electron transport. Chemical studies on the reduction and oxidation of the spin label show that loss of signal is due to reduction and not destruction of the label. No evidence was found for flip-flop of the label in submitochondrial preparations. Spin reduction of respiring mitochondria, mitoplasts, or inverted submitochondrial preparations is inhibited by rotenone but is relatively insensitive to antimycin A and KCN. Because the midpoint potentials of the spin labels were found to be similar to that of ubiquinone, it is concluded that reducing equivalents of mitochondrial electron transport from this region of the chain are channeled to either membrane interface.
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PMID:Surface localization of sites of reduction of nitroxide spin-labeled molecules in mitochondria. 19 15

Distinct increase in biosynthesis of ubiquinone and sterols was observed in regenerating liver tissue of rats; the rate of ubiquinone degradation was not altered. This phenomenon was characterized by incorporation of 14C-tyrosine into ubiquinone and of I-14C-acetate into ubiquinone and sterols in vivo and in vitro. An increased turnover of enzymes, participating in synthesis of the substances, was found in cytoplasm and mitochondria of regenerating liver after administration into animals with subtotal hepatectomy of specific inhibitors: cycloheximide, ethidium bromide, hydroxytetracycline, cholesterol and cholesterol with bile; relative rates of labelled precursors incorporation into ubiquinone and sterols were then estimated in vitro. The highest rate of I-14C-pacetate incorporation into ubiquinone was found within 24 hrs after hepatectomy, into sterols--within 48 hrs and 72 hrs after hepatectomy. Mitochondrial DNA appear to code certain functional proteins responsible for synthesis of ubiquinone in mitochondria. The enzymes, which formed precursors of isoprenoid substances in cytoplasm, were shown to regulate ubiquinone biosynthesis. Regulation of ubiquinone biosynthesis in regenerating liver is discussed.
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PMID:[Regulation of ubiquinone metabolism: a study in the regenerating rat liver]. 66 50

Effect of cycloheximide, ethidium bromide and hydroxytetracycline on incorporation of label from I-14C-acetate into ubiquinone and cholesterol as well as from diffusively labelled 14C-tyrosine into ubiquinone was studied in slices of rat hypertrophic kidney within 2 days after unilateral nephrectomy. Incorporation of these labels into ubiquinone and of 1-14C-acetate into cholesterol was distinctly increased using slices of hypertrophic kidney. Repeated administration of cycloheximide just after the operation and within 24 hrs after it depressed the kidney hypertrophy, inhibited completely the label incorporation into cholesterol and partially - into ubiquinone. This suggests that the rate of enzymes production, responsible for synthesis of these substances, is increased in hypertrophic kidney. Injection of ethidium bromide after the operation inhibited distinctly the label incorporation into ubiquinone and did not effect on incorporation of 1-14C-acetate into cholesterol. Hydroxytetracycline proved to be ineffective in these labels incorporation. Mitochondrial DNA appears to participate in coding of some functionally active proteins responsible for ubiquinone biosynthesis.
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PMID:[Activation of the incorporation of labeled precursors into ubiquinone in slices of rat hypertrophied kidney]. 66 87

Searches of the protein data bases revealed limited homologies between several regions of the human erythrocyte glucose transporter containing a relative abundance of hydrogen-bonding amino-acid side chains, and proteins of the NADH-ubiquinone oxidoreductase family. This raised the possibility the binding sites for glucose and ubiquinone may be similar in the respective proteins. Experimental studies demonstrated that ubiquinone Q0 does in fact inhibit both glucose entry and glucose exit in human erythrocytes with kinetics consistent with the existence of ubiquinone binding sites at both the exofacial and endofacial sides of the transporter. Glucose transport was also inhibited by the water-soluble tryptophan-inactivating agent, dimethyl(2-hydroxy-5-nitrobenzyl)sulphonium bromide, and this is consistent with the presence of tryptophan residues in two of the exofacial amino-acid sequences proposed as candidates for involvement in glucose binding sites.
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PMID:Inhibition of glucose transport in human erythrocytes by ubiquinone Q0. 193 61

MPP+, an oxidative metabolite of a neurotoxin, MPTP, was found to be cytotoxic to human melanoma cell lines, HMV-II and SK-MEL-44. After 3 days of culture in the presence of MPP+, a larger amount of MPP+ was accumulated in HMV-II cells than in SK-MEL-44 cells, which correlated well with the melanin contents; HMV-II cells contain larger amounts of melanin than SK-MEL-44 cells. After 6 days of culture in the presence of MPP+, the cytotoxicity of MPP+ on these cell types was evaluated by counting cell numbers with the dye exclusion test and double-layer soft agar clonogenic assay. It was found that exposure to MPP+ reduced the survival of HMV-II cells more significantly than that of SK-MEL-44 cells. In HMV-II cells, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay was used to elucidate the mechanism of MPP+ lethality. The formazan formation was reduced markedly by the presence of MPP+ at concentrations much lower than those required for cell death. These results suggest that cytotoxicity of MPP+ may be ascribed to its accumulation due to high affinity for melanin, and to inhibition of the enzymes utilizing ubiquinone in the mitochondrial respiratory chain.
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PMID:Cytotoxic effect of 1-methyl-4-phenylpyridinium ion on human melanoma cell lines, HMV-II and SK-MEL-44, is dependent on the melanin contents and caused by inhibition of mitochondrial electron transport. 239 Feb 89

The effects of tetragalloylglucose (1,2,3,6-tetra-O-galloyl-beta-D-glucose) on purified complex II (succinate-ubiquinone oxidoreductase) of the mitochondrial electron transport system of Ascaris muscle were studied. Both succinate-ubiquinone-1 (Q1) oxidoreductase, and succinate dehydrogenase measured with 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) in the presence of phenazine methosulfate (PMS) were inhibited by tetragalloylglucose. The inhibitions of both reductase activities of complex II were of competitive type, and the inhibitor constant (Ki) for Ascaris complex II (148 nM) was lower than that for rat liver complex II (1.5 microM). Thus, Ascaris complex II is much more sensitive to this inhibitor than the mammalian counterpart.
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PMID:Inhibitory effects of tetragalloylglucose on the complex II of mitochondrial respiratory chain of Ascaris muscle. 260 4

The amino acid sequence of the ubiquinone binding protein (QP-C) in the cytochrome bc1 region of the mitochondrial electron transfer chain was determined by analysis of peptides obtained by cyanogen bromide cleavage and staphylococcal protease digestion of succinylated derivatives. It was found to consist of 110 amino acid residues and its amino terminus to be blocked by an acetyl group, as determined by mass spectrometry of the amino-terminal peptide and a comparison with peptides chemically synthesized on high-performance liquid chromatography. The molecular weight of this ubiquinone binding protein including the acetyl group was calculated to be 13,389. The predicted secondary structure of QP-C has alpha-helical content of about 50% and QP-C was classified as an "all-alpha" or "alpha + beta" protein. This is the first report describing the amino acid sequence of the ubiquinone binding protein. A comparison of this sequence with that of the 14-kDa subunit of the yeast ubiquinol-cytochrome c reductase complex from the nucleotide sequence showed these two sequences to be quite similar.
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PMID:Complete amino acid sequence of the ubiquinone binding protein (QP-C), a protein similar to the 14,000-dalton subunit of the yeast ubiquinol-cytochrome c reductase complex. 298 Dec 8

Phagocytic vesicles with superoxide-forming NADPH oxidase activity were obtained from human monocytes phagocytosing oil droplets. The superoxide-forming activity in the monocyte vesicles increased for the first 5 min during incubation with oil droplets and remained constant for 30 min. NADPH-dependent activities of 2,6-dichlorophenol-indophenol (DCIP) reduction and ubiquinone-1 (Q1) reduction were found in the vesicles and the activities were closely associated with the superoxide-forming oxidase. The values of apparent Km for NADPH of these three activities were essentially the same and the activities were inhibited with a similar pattern by p-chloromercuribenzoate and a cationic detergent, cetyltrimethylammonium bromide. The activities were extremely labile and the DCIP reductase activity was most labile. The superoxide-forming oxidase and the Q1 reductase could be extracted with a mixture of deoxycholate and Tween-20. The extracted activities were not enhanced by the addition of FAD.
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PMID:NADPH-dependent superoxide-forming oxidase in phagocytic vesicles of human monocytes. 374 37

NADPH-dependent ubiquinone-1 reductase activity was present in the phagocytic vesicles of pig polymorphonuclear leucocytes. The apparent Km-value of the reductase for NADPH was 29 microM which is similar to that of the NADPH-dependent superoxide formation. Increase of the quinone-reductase activity by increasing the concentrations of ubiquinone-1 was associated with the decrease of the superoxide forming activity, the rate of the NADPH oxidation being constant independent of the quinone concentration. p-Chloromercuribenzoate inhibited both superoxide formation and reduction of the quinone, whereas low concentrations of cetyltrimethylammonium bromide which inhibit the superoxide formation did not inhibit the reduction of the quinone. The reduction of 2,6-dichlorophenolindophenol which has been shown not to be inhibited by both inhibitors. The quinone-reductase activity could be extracted with a mixture of deoxycholate and Tween 20 which extracts the superoxide forming activity. The observations indicate that a region of the superoxide-forming NADPH oxidase between a mercurial-sensitive site and a site sensitive to the cationic detergent is responsible for the reduction of ubiquinone.
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PMID:NADPH-dependent reduction of ubiquinone-1 associated with the superoxide-forming oxidase of pig polymorphonuclear leucocytes. 642 94

Highly purified preparations of the cholate-solubilized respiratory NADH dehydrogenase, isolated from genetically amplified Escherichia coli strains [Jaworowski, A., Campbell, H. D., Poulis, M. I., & Young, I. G. (1981) Biochemistry 20, 2041-2047], have been characterized. Enzyme preparations were shown to contain 70% (w/w) lipid, predominantly phosphatidylethanolamine. One mol of noncovalently bound FAD and approximately 1 mol of ubiquinone/mol of enzyme subunit were detected. The purified enzyme was shown to contain only low levels of Fe and acid-labile S, indicating the absence of iron-sulfur clusters. No Cu, Mo, W, or covalently bound P was detected, and no evidence for other chromophores was obtained from visible and ultraviolet absorption spectra of the purified enzyme or of the delipidated polypeptide prepared by gel filtration in sodium dodecyl sulfate. Protein chemical studies verified that the enzyme consists of a single polypeptide species of Mr 47 000, and the N- and C-terminal cyanogen bromide peptides were identified. The pure enzyme was shown to reconstitute membrane-bound, cyanide-sensitive NADH oxidase activity in membrane vesicles prepared from ndh mutant strains.
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PMID:Characterization of the respiratory NADH dehydrogenase of Escherichia coli and reconstitution of NADH oxidase in ndh mutant membrane vesicles. 702 Jul 57


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