Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Triphenylsulphonium ions inhibit mitochondrial oxidative phosphorylation and adenosine triphosphatase activity. The site of action is on the soluble F1 adenosine triphosphatase component. Triphenylsylphonium ions also inhibit electron transfer in the NAD-cytochrome b region of the respiratory chain. In both types of inhibition, triphenylsulphonium ions are effective at low concentrations, half-maximal inhibition being produced by a concentration of about 20-30 muM. These effects resemble the effects of alkylguanidines on mitochondria and are discussed in relation to the effects of alkylguanidines and other lipophilic cations such as ethidium and dibenzyldimethylammonium ions. A modification of the purification procedure for the soluble mitochondrial adenosine triphosphatase [Beechey, Hubbard, Linnett, Mitchell & Munn (1975) Biochem. J. 148, 533-537] IS DESCRIBED, WHICH YIELDS A PREPARATION WITH A HIGHER SPECIFIC ACTIVITY AND SHOWING FEWER BANDS IN GEL ELECTROPHORESIS.
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PMID:Effects of triphenylsulphonium ions on mitochondria. Inhibition of adenosine triphosphatase activity. 13 79

the toxic effects of CH3HgCL on mitochondria of mammalian organs including human and rat liver were examined. [203Hg]CH3HGCl was bound mainly to mitochondrial proteins. The binding was not effected by the energy state of mitochondria. The state 3 respiration, oxidative phosphorylation and 32Pi-ATP exchange reaction were inhibited by 10 to 50 nmol of CH3HgCl per mg of mitochondrial protein, while NADH-and succinate-dehydrogenase and ATPase were more resistant to it The difference spectrum of the treated mitochondria indicated that the point of inhibition was located after flavin and before cytochrome b. Mitochondrial swelling was induced by CH3HgCl, in accordance with previous morphological observations in vivo. The swelling, stimulation of ATPase and energy-dependent H+ extrusion cauded by CH3HgCl were equally dependent on K+. Under these conditions, uptake of K+ by mitochondria was increased and the membrane potential was dissipated. Unlike the case with other organomercuric compounds, transport of phosphate was not inhibited by CH3HgCl. When tested on liposomes, CH3HgCl itself was not lipid-soluble, as some organomercuric compounds are, and was not an uncoupler or a K+-carrier. It was concluded that protein bound CH3HgS-induced K+ uptake into mitochondria and the resulting loss of membrane potential was the major cause of uncoupling, though at higher concentrations, the electron transport system was also inhibited.
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PMID:Effect of methyl mercury on phosphorylation, transport, and oxidation in mammalian mitochondria. 14 24

1. The properties of membrane vesicles from the extreme thermophile Bacillus caldolyticus were investigated. 2. Vesicles prepared by exposure of spheroplasts to ultrasound contained cytochromes a, b and c, and at 50 degrees C they rapidly oxidized NADH and ascorbate in the presence of tetramethyl-p-phenylenediamine. Succinate and l-malate were oxidized more slowly, and dl-lactate, l-alanine and glycerol 1-phosphate were not oxidized. 3. In the absence of proton-conducting uncouplers the oxidation of NADH was accompanied by a net translocation of H(+) into the vesicles. Hydrolysis of ATP by a dicyclohexylcarbodi-imide-sensitive adenosine triphosphatase was accompanied by a similarly directed net translocation of H(+). 4. Uncouplers (carbonyl cyanide p-trifluoromethoxyphenylhydrazone or valinomycin plus NH(4) (+)) prevented net H(+) translocation but stimulated ATP hydrolysis, NADH oxidation and ascorbate oxidation. The last result suggested an energy-conserving site in the respiratory chain between cytochrome c and oxygen. 5. Under anaerobic conditions the reduction of cytochrome b by ascorbate (with tetramethyl-p-phenylenediamine) was stimulated by ATP hydrolysis, indicating an energy-conserving site between cytochrome b and cytochrome c. However, no reduction of NAD(+) supported by oxidation of succinate, malate or ascorbate occurred, neither did it with these substrates in the presence of ATP under anaerobic conditions, suggesting that there was no energy-conserving site between NADH and cytochrome b. 6. Succinate oxidation, in contrast with that of NADH and ascorbate, was strongly inhibited by uncouplers and stimulated by ATP hydrolysis. These effects were not observed when phenazine methosulphate, which transfers electrons from succinate dehydrogenase directly to oxygen, was present. It was concluded that in these vesicles the oxidation of succinate was energy-dependent and that the reoxidation of reduced succinate dehydrogenase was dependent on the outward movement of H(+) by the protonmotive force. 7. In support of the foregoing conclusion it was shown that the reduction of fumarate by NADH was an energy-conserving process. 8. If the activities of vesicles accurately represent those of the intact organism it appears that in B. caldolyticus the reduction of fumarate to succinate at the expense of reducing equivalents from NADH is energetically favoured over succinate oxidation even under aerobic conditions. This may be related to the need for an ample supply of succinate for haem synthesis in order to provide cytochromes for the organism.
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PMID:The oxidative activities of membrane vesicles from Bacillus caldolyticus. Energy-dependence of succinate oxidation. 20 11

ATP synthesis was measured after chromatophores from Rhodopseudomonas capsulata had been subjected to illumination by single turnover flashes fired at variable frequencies. Three processes were examined, which under different conditions can limit the net yield of ATP. (1) A process with an apparent relaxation time of 10-20 ms. This reaction probably limits the rate of ATP synthesis in continuous illumination. It has similar time dependence to the stimulation of the carotenoid shift decay by ADP after a single flash. (2) An active state of the ATPase only persists when the chromatophores are excited more often than once in 10 s. This state decays with similar kinetics to the entire carotenoid shift decay. Full activation is achieved after two flashes. (1) and (2) are not significantly affected by concentrations of antimycin A sufficient to block electron flow through the cytochrome b/c2 oxidoreductase and abolish phase III in the generation of the carotenoid shift. (3) In the presence of antimycin A, after the third, fourth and subsequent flashes ATP synthesis is limited by the quantity of reducing equivalents transported through the reaction centre rather than by the level of the electrochemical proton gradient.
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PMID:Kinetic factors limiting the synthesis of ATP by chromatophores exposed to short flash excitation. 22 28

We propose that the UGA terminator regularly occurs as a tryptophan codon in yeast mitochondrial DNA. This conclusion is based on the sequence analysis of mitochondrial DNA regions coding for structural genes of cytochrome b, cytochrome oxidase, and the ATPase.
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PMID:Use of the UGA terminator as a tryptophan codon in yeast mitochondria. 22 81

Ethanol and acetaldehyde, alone or in combination, at physiologic concentrations, significantly inhibit mitochondrial protein synthesis in vitro. Mitochondria from rats chronically fed ethanol also display a reduced rate of mitochondrial protein synthesis in vitro. This effect is further aggravated by addition of ethanol to the incubation medium. Sodium dodecyl sulfate-gel electrophoresis of mitochondria fractionated with acetic acid-lubrol, which were incubated in the presence of ethanol or acetaldehyde, revealed a modest over-all decrease in labeling. However, a polypeptide fraction in the molecular weight range of 36,000 to 40,000 was conspicuously decreased. This range includes subunits of cytochrome oxidase, cytochrome b, and ATPase. Liver mitochondria from rats fed ethanol chronically showed a comparable decrease in the 36,000- to 40,000-molecular weight peak after incubation with radioactive leucine in vitro and fractionation with acetic acid-lubrol. Similar results were obtained when mitochondrial protein synthesis was determined in vivo in chronically treated rats. The data suggest that chronic ethanol consumption interferes with mitochondrial membrane biogenesis and that several products are more sensitive to this effect than others.
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PMID:The effects of ethanol and acetaldehyde on the products of protein synthesis by liver mitochondria. 50 71

Mitochondrial function and structure in cirrhotic livers from humans or rats show a variety of changes as compared to control livers. Mitochondrial ATP production is reduced in rats with CCl4- or thioacetamide-induced liver cirrhosis and in rats with secondary biliary cirrhosis. Activity of the electron transport chain is decreased in rats with secondary biliary cirrhosis. In rats with CCl4-induced cirrhosis, the mitochondrial content of certain constituents of the respiratory chain (cytochrome a + a3, cytochrome b and ubiquinone) is increased and activities of cytochrome c oxidase and ATPase are elevated. Similarly, in humans with liver cirrhosis, mitochondrial cytochrome a + a3 content is elevated and has been used to assess the risk for hepatectomy. In rats with secondary biliary cirrhosis, compensatory strategies include increased mitochondrial volume per hepatocyte and possibly increased extramitochondrial ATP production (increased glycolysis). Thus, a variety of adaptive mechanisms are used to maintain mitochondrial function in cirrhotic livers.
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PMID:Adaptation of mitochondrial metabolism in liver cirrhosis. Different strategies to maintain a vital function. 129 65

Previous work has shown that irrespective of the route of exposure methyl isocyanate (MIC) caused acute lactic acidosis in rats (Jeevaratnam et al., Arch. Environ. Contam. Toxicol. 19, 314-319, 1990) and the hypoxia was of stagnant type due to tissue hypoperfusion resulting from hypovolemic hypotension in rabbits administered MIC subcutaneously (Jeevarathinam et al., Toxicology 51, 223-240, 1988). The present study was designed to investigate whether MIC could induce histotoxic hyperoxia through its effects on mitochondrial respiration. Male Wistar rats were used for liver mitochondrial and submitochondrial particle (SMP) preparation. Addition of MIC to tightly coupled mitochondria in vitro resulted in stimulation of state 4 respiration, abolition of respiratory control, decrease in ADP/O ratio, and inhibition of state 3 oxidation. The oxidation of NAD(+)-linked substrates (glutamate + malate) was more sensitive (five- to sixfold) to the inhibitory action of MIC than succinate while cytochrome oxidase remained unaffected. MIC induced twofold delay in the onset of anerobiosis, and cytochrome b reduction in SMP with NADH in vitro confirms inhibition of electron transport at complex I region. MIC also stimulated the ATPase activity in tightly coupled mitochondria while lipid peroxidation remained unaffected. As its hydrolysis products, methylamine and N,N'-dimethylurea failed to elicit any change in vitro; these effects reveal that MIC per se acts as an inhibitor of electron transport and a weak uncoupler. Administration of MIC sc at lethal dose caused a similar change only with NAD(+)-linked substrates, reflecting impairment of mitochondrial respiration at complex I region and thereby induction of histotoxic hypoxia in vivo.
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PMID:In vitro and in vivo effect of methyl isocyanate on rat liver mitochondrial respiration. 147 Nov 48

Disruption of the gene for subunit 6 of the yeast cytochrome bc1 complex (QCR6) causes a temperature-sensitive petite phenotype in contrast to deletion of the coding region of QCR6, which shows no growth defect. Mitochondria from the petite strain carrying the disruption allele were devoid of ubiquinol-cytochrome c oxidoreductase activity but retained cytochrome c oxidase and oligomycin-sensitive ATPase activities. Optical spectra of cytochromes in mitochondrial membranes from the petite strain lacked a cytochrome b absorption band and had a reduced amount of cytochrome c1. Analysis of mitochondrial translation products showed normal synthesis of cytochrome b. Western analysis of mitochondrial membranes from this disruption strain indicates core protein 1 of the cytochrome bc1 complex is present in normal amounts, while cytochrome c1, the Rieske iron-sulfur protein, subunit 6, and subunit 7 were absent or present in very low amounts. Taken together, these findings indicate a loss of assembly of the cytochrome bc1 complex. High copy suppressors of the disruption strain were selected. Two separate families of suppressors were found. The first contained QCR6. The second family consisted of overlapping clones of a second gene distinct from QCR6. These plasmids contained QCR9, the gene which codes for subunit 9 of the yeast cytochrome bc1 complex. Suppression of the QCR6 disruption strain by overexpression of QCR9 indicates a critical interaction between these two proteins in the assembly of the cytochrome bc1 complex.
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PMID:The petite phenotype resulting from a truncated copy of subunit 6 results from loss of assembly of the cytochrome bc1 complex and can be suppressed by overexpression of subunit 9. 165 16

To investigate whether RNA editing in plant mitochondria modifies structural RNAs as well as protein-coding RNAs we compared the genomic-encoded information with the respective transcripts of several genes in Oenothera. The genes analysed are the 5S, 18S and 26 S rRNAs, the alpha-subunit of ATPase (atpA), cytochrome b (cytb), orfB, which is located upstream of cytochrome oxidase subunit III, and the respective leader, trailer and spacer sequences. All open reading frames were found to be edited to some degree. The atpA coding region has the least edited mRNA in Oenothera mitochondria, with only four nucleotides altered in the 1533 nucleotide open reading frame. From this analysis we conclude that frequent RNA editing is indicative of functional protein coding regions in plant mitochondria. The extensive editing in orfB, for example, suggests that this orf codes for a mitochondrial protein. No RNA editing event was found in the 5S rRNA or in the 1824 nucleotides analysed of the 18S rRNA, but two nucleotides were found to be altered in the 1970 nucleotides compared for the 26S rRNA. One nucleotide alteration has changed C to U, the other in reverse U to C. However, only one of five cDNA clones covering this region shows the modifications, similar to many silent editing events in open reading frames. RNA editing in the structural RNAs thus does not seem to be essential for their function in the mitochondrial ribosome.
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PMID:Distribution of RNA editing sites in Oenothera mitochondrial mRNAs and rRNAs. 172 5


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