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:3.6.3.14 (ATP synthase)
7,042 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In this study we report the first comparison of the mitochondrial protein import and processing events in two different tissues from the same organism. Both spinach leaf and root mitochondria were able to import and process the in vitro transcribed and translated Neurospora crassa F1 beta subunit of ATP synthase to the mature size product. Temperature optimum for protein import, 20 degrees C, was considerably lower than that found in other systems. In spinach leaf mitochondria, the processing peptidase has been shown to constitute an integral part of the bc1 complex of the respiratory chain. In accordance with these results, the majority of the processing activity in root mitochondria was also localized in the membrane. However, although the same amount of the processing peptidase was present per mg of membrane protein in both leaf and root mitochondria, as determined immunologically, the specific processing activity was several-fold higher in roots. Furthermore, in contrast to the processing enzyme in leaf, a portion of the processing activity could be disassociated from the root membrane with relatively weak salt treatment. The processing event in both the leaf and root membranes was always accompanied by a degradation of the F1 beta precursor. The degradation activity was found to be several-fold higher in roots than in leaves and was also partially dissociated from the membrane after salt treatment. Both the processing and degradation activities were inhibited by orthophenanthroline, a known metalloprotease inhibitor. These results show tissue-specific differences of the processing event catalyzed by the bc1 complex and indicate the presence of two populations of the processing peptidase in root mitochondria.
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PMID:Tissue-specific differences of the mitochondrial protein import machinery: in vitro import, processing and degradation of the pre-F1 beta subunit of the ATP synthase in spinach leaf and root mitochondria. 794 13

Recent studies have suggested that modifications in mitochondrial F1-adenosinetriphosphatase (ATPase) activity may play an important role in the regulation of myocardial oxidative phosphorylation. The goal of the present study was to develop and characterize an assay of F1-ATPase activity that could be performed repeatedly on an intact heart under various physiological states. With the use of submitochondrial particles prepared from biopsy samples of canine myocardium, we found reproducible F1-ATPase activity when normalized to the activity of the intramitochondrial enzyme citrate synthase. The oligomycin-sensitive component of the ATPase activity was found to be mainly F1-ATPase. F1-ATPase activity of normal myocardium increased by incubation in high salt-pH buffer, suggesting baseline inhibition. Five minutes after global ischemia, F1-ATPase activity decreased to 60% of baseline. Hypoxia for 10 min resulted in no significant change in F1-ATPase activity. With phenylephrine infusion, myocardial oxygen consumption more than doubled, whereas F1-ATPase activity increased by approximately 30%. Both returned to baseline levels after discontinuation of the drug. With the use of an assay developed to measure F1-ATPase activity of intact myocardium, changes of the enzyme activity were found during both ischemia and at increased work loads. These data suggest that alterations of F1-ATPase activity may contribute to the regulation of myocardial oxidative phosphorylation.
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PMID:Mitochondrial F1-ATPase activity of canine myocardium: effects of hypoxia and stimulation. 802 1

Studies with the yeast mitochondrial F1-ATPase showed that non-Michaelis-Menten kinetics occurred around pH 8 when there was an excess of magnesium over ATP and a low salt concentration. Increasing the salt concentration activated the enzyme and resulted in Michaelis-Menten kinetics. In contrast, increasing the salt concentration had no effect when ATP was in excess of magnesium. The data were interpreted to mean that magnesium ions inhibit by limiting the amount of free ATP and that the salt anions are able to overcome this effect by replacing the ATP. Mechanistically this is consistent with a ligand substitution reaction in which either free ATP or salt anions are required to displace a product from the enzyme.
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PMID:Yeast mitochondrial F1-ATPase: the unusual kinetics with excess magnesium ions at low salt concentrations. 805 94

Toxic bile salts cause hepatocyte necrosis at high concentrations and apoptosis at lower concentrations. Although fructose prevents bile salt-induced necrosis, the effect of fructose on bile salt-induced apoptosis is unclear. Our aim was to determine if fructose also protects against bile salt-induced apoptosis. Fructose inhibited glycochenodeoxycholate (GCDC)-induced apoptosis in a concentration-dependent manner with a maximum inhibition of 72% +/- 10% at 10 mmol/L. First, we determined if fructose inhibited apoptosis by decreasing adenosine triphosphate (ATP) and intracellular pH (pHi). Although fructose decreased ATP to <25% of basal values, oligomycin (an ATP synthase inhibitor) did not inhibit apoptosis despite decreasing ATP to similar values. Fructose (10 mmol/L) decreased intracellular pH (pHi) by 0.2 U. However, extracellular acidification (pH 6.8), which decreased hepatocyte pHi 0.35 U and is known to inhibit necrosis, actually potentiated apoptosis 1.6-fold. Fructose cytoprotection also could not be explained by induction of bcl-2 transcription or metal chelation. Because we could not attribute fructose cytoprotection to metabolic effects, alterations in the expression of bcl-2, or metal chelation, we next determined if the poorly metabolized ketohexoses, tagatose and sorbose, also inhibited apoptosis; unexpectedly, both ketohexoses inhibited apoptosis. Because bile salt-induced apoptosis and necrosis are inhibited by fructose, these data suggest that similar processes initiate bile salt-induced hepatocyte necrosis and apoptosis. In contrast, acidosis, which inhibits necrosis, potentiates apoptosis. Thus, ketohexose-sensitive pathways appear to initiate both bile salt-induced cell apoptosis and necrosis, whereas dissimilar, pH-sensitive, effector mechanisms execute these two different cell death processes.
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PMID:Cytoprotection by fructose and other ketohexoses during bile salt-induced apoptosis of hepatocytes. 898 69

Alkaliphilic Bacillus species that are isolated from nonmarine, moderate salt, and moderate temperature environments offer the opportunity to explore strategies that have developed for solving the energetic challenges of aerobic growth at pH values between 10 and 11. Such bacteria share many structural, metabolic, genomic, and regulatory features with nonextremophilic species such as Bacillus subtilis. Comparative studies can therefore illuminate the specific features of gene organization and special features of gene products that are homologs of those found in non-extremophiles, and potentially identify novel gene products of importance in alkaliphily. We have focused our studies on the facultative alkaliphile Bacillus firmus OF4, which is routinely grown on malate-containing medium at either pH 7.5 or 10.5. Current work is directed toward clarification of the characteristics and energetics of membrane-associated proteins that must catalyze inward proton movements. One group of such proteins are the Na+/H+ antiporters that enable cells to adapt to a sudden upward shift in pH and to maintain a cytoplasmic pH that is 2-2.3 units below the external pH in the most alkaline range of pH for growth. Another is the proton-translocating ATP synthase that catalyzes robust production of ATP under conditions in which the external proton concentration and the bulk chemiosmotic driving force are low. Three gene loci that are candidates for Na+/H+ antiporter encoding genes with roles in Na(+)-dependent pH homeostasis have been identified. All of them have homologs in B. subtilis, in which pH homeostasis can be carried out with either K+ or Na+. The physiological importance of one of the B. firmus OF4 loci, nhaC, has been studied by targeted gene disruption, and the same approach is being extended to the others. The atp genes that encode the alkaliphile's F1F0-ATP synthase are found to have interesting motifs in areas of putative importance for proton translocation. As an initial step in studies that will probe the importance and possible roles of these motifs, the entire atp operon from B. firmus OF4 has been cloned and functionally expressed in an Escherichia coli mutant that has a full deletion of its atp genes. The transformant does not exhibit growth on succinate, but shows reproducible, modest increases in the aerobic growth yields on glucose as well as membrane ATPase activity that exhibits characteristics of the alkaliphile enzyme.
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PMID:pH homeostasis and ATP synthesis: studies of two processes that necessitate inward proton translocation in extremely alkaliphilic Bacillus species. 978 68

The head piece separated from the A-ATP synthase of Halobacterium halobium hydrolyses ATP. This A1-ATPase is inhibited by nitrate but not by other chaotropic anions. The nitrate inhibition is noncompetitive with respect to ATP, reversible, and partially protected by chloride. In contrast, ATP synthase in situ (A1Ao-ATPase) is not inhibited by nitrate but apparently is inhibited by stronger chaotropic reagents, such as thiocyanate and trichloroacetate, which make the vesicle membrane permeable to protons. The mode of action of nitrate and chaotropic anions seems to differentiate A-ATPases from V-ATPases. Other strains of Halobacterium, Haloferax, Haloarcula, Halococcus and Natronobacterium, contain at least two polypeptides immunochemically similar to the two major subunits, (&agr;) (86x10(3 )Mr on SDS-PAGE) and &bgr; (64x10(3 )Mr), of the A-ATPase of Halobacterium halobium. When solubilized, membrane vesicles of these halobacteria hydrolyse ATP. Their ATPases are commonly sensitive to nitrate. They require high concentrations of the supporting salt but depend differently on chloride or sulfate/sulfite. The A-ATPases of Halobacteriaceae appear to diverge with respect to salt preference.
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PMID:HALOBACTERIAL A-ATP SYNTHASE IN RELATION TO V-ATPase. 987 57

Thorough analysis of the cta operon of Synechocystis sp. PCC6803 (grown in high-concentration salt medium to enhance the expression of respiratory proteins) showed that, apart from ctaCDE and Fb genes potentially encoding subunits I, II, III, and a small pseudo-bacteria-like subunit-IV of unknown function, a large mitochondria-like cta-Fm gene and a pronounced terminator structure are additional components of the operon. The deduced cta Fm gene product shows approximately 50% and 20% sequence identity to the Saccharomyces cerevisiae and beef heart mitochondrial COIV proteins, respectively. It also shows amino acid regions (near the N terminus, on the cytosolic side) with conspicuous sequence similarities to adenylate-binding proteins such as ATP synthase beta subunit Walker A and B consensus regions or to adenylate kinase. We suggest that, similar to the situation with beef heart mitochondria, it is the mitochondria-like subunit-IV of the cyanobacterial aa3-type cytochrome-c oxidase that confers allosteric properties to the cyanobacterial enzyme, the H+/e- ratios of cytochrome c oxidation being significantly lowered by ATP (intravesicular or intraliposomal) but enhanced by ADP. Therefore, the antagonistic action of ATP and ADP was in a way that the redox reaction proper, was always significantly less affected than the coupled proton translocation. Evolutionary and ecological implications of the unusual allosteric regulation of a prokaryotic cytochrome-c oxidase is discussed.
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PMID:Allosteric properties of cyanobacterial cytochrome c oxidase: inhibition of the coupled enzyme by ATP and stimulation by ADP. 1079 96

The mixed-valence compound [(NC)(5)Fe(II)-Im-Ru(III)(NH(3))(5)](-),M(i), was prepared in solution and as a solid sodium salt from [Fe(CN)(5)H(2)O](3)(-) and [Ru(NH(3))(5)Im](2+). The binuclear complex shows two bands at 366 nm (epsilon = 3350 M(-)(1) cm(-)(1)) and 576 nm (epsilon = 1025 M(-)(1) cm(-)(1)), assigned as LMCT transitions, as well as a near-IR band at 979 nm (epsilon = 962 M(-)(1) cm(-)(1)) associated with an intervalence transition. By calculation of the Hush model parameters alpha(2) and H(ab) (delocalization and electronic coupling factors, respectively), the complex is defined as a valence-trapped Fe(II)-Ru(III) system; this is confirmed by the measured redox potentials at -0.20 V and 0.30 V, associated with redox processes at the ruthenium and iron center, respectively. The formation stability constant of the mixed-valence ion was obtained through independent measurements of k(f) and k(d), the formation and dissociation specific rate constants, respectively. The stabilization of M(i) with respect to disproportionation into the isovalent states, as well as toward the formation of the electronic isomer, Fe(III)-Im-Ru(II), was also estimated. The fully reduced (R(i)) and fully oxidized (O(i)) binuclear complexes were prepared in solution and characterized by UV-vis spectroscopy. The kinetics of the reactions of R(i) and M(i) with peroxydisulfate were measured and a mechanistic analysis was performed, showing the relevance of electronic isomerization in completing the full conversion to O(i), through the assistance of the Ru(II)(NH(3))(5)(2+) center in the oxidation of the neighboring Fe(II)(CN)(5)(3)(-) moiety. The latter results are compared with those obtained with related complexes comprising different X(5)M-L moieties bound to Ru(II)(NH(3))(5)(2+). A linear correlation is displayed by plotting ln k(et) against E degrees (Ru), associated with the intramolecular oxidation rate constant of Ru(II) in the ion pair (binuclear species + peroxydisulfate) and the reduction potential of the corresponding Ru(III,II) couple in the ion pair.
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PMID:Electronic Structure and Substitution and Redox Reactivity of Imidazolate-Bridged Complexes of Pentacyanoferrate and Pentaammineruthenium. 1166 18

The biological activity of lysosomotropic n-alkyl N,N-dimethylglycinates (DMG-n) was compared with that of a quaternary ammonium salt IM (methochloride of DMG-12). The activity of the glycinates appeared to be carbon chain length dependent and was similar at pH 6 and pH 8. Nutritional auxotrophy and respiratory deficiencies have no influence on DMG-n sensitivity. Both IM and DMG-n inhibit plasma membrane H+-ATPase activity while mitochondrial ATPase is relatively non-sensitive to glycinates. No cross-resistance to IM and DMG-n was observed.
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PMID:Comparative studies of the biological activities of lysosomotropic aminoesters and quaternary ammonium salts on the yeast Saccharomyces cerevisiae. 1175 34

The study of the binding of the nucleotides ADP and ATP on the exchangeable sites of chloroplast ATPase CF1 has been carried out by the Hummel and Dreyer method applied to HPLC. It has been shown that this method was well fitted to the problem: rapidity of exchange, absence of noticeable modification after binding, presence of a constant concentration of ligand during the chromatography, which stabilizes these low affinity complexes. The dissociation constants of binding of ADP, ATP and of their magnesium salt complexes have been determined. In order to measure the simultaneous binding of ADP and ATP when present in mixture, we have modified the method by using an anion-exchange column in place of the gel filtration column: the two nucleotides were easily separated, while the binding on the protein was unchanged. The extension of this method to the reversed-phase chromatography could also be considered for the binding of hydrophobic ligands.
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PMID:Use of the hummel and dreyer method for the study of nucleotide binding on chloroplast ATPase CF1. 1193 50


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