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:1.9.3.1 (cytochrome oxidase)
8,822 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Determinations of iron content and dry-weight measurements on samples of Pseudomonas cytochrome oxidase were coupled with sodium dodecyl sulphate/polyacrylamide-gel-electrophoresis studies of both the native protein and covalently cross-linked oligomers in order to estimate the enzyme's molecular weight and spectral absorption coefficients. A value of epsilon(ox.) (410)=282x10(3) litre.mol(-1).cm(-1) was calculated for a dimeric protein molecule having a total molecular weight of 122000 (based on iron analysis). Steady-state kinetic observations of the enzyme-catalysed oxidation of reduced azurin by nitrite indicated a marked increase in enzyme inactivation as the pH was raised from 5.7 to 7.2. Since NO, a product of the nitrite reductase activity of Pseudomonas cytochrome oxidase, is known to bind to the enzyme, a study was undertaken to try to assess the potential of NO as a product inhibitor. Investigations showed that samples of the oxidized protein at pH values 4, 5 and 6 bound NO to both haem c and d(1) components, but oxidized enzyme samples at pH7 and above formed their reduced ligand-bound forms when placed under an atmosphere of the gas. Ascorbate-reduced enzyme samples at pH4, 5, 6 and 7 were also found to bind NO at both haem components, although at pH7 the rate of haem c binding was very slow. At pH8 and 9 only the ferrohaem d(1) bound NO. Titration experiments on the reduced protein over the pH range 5-7, with nitrite as a precursor of NO, showed that the haem d(1) had a much higher affinity than the haem c: experiments at pH5.2 and 5.9 with NO-equilibrated solutions revealed the same pattern of behaviour with the oxidized enzyme.
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PMID:A re-evaluation of some basic structural and functional properties of Pseudomonas cytochrome oxidase. 4 92

1. Beef heart mitochondria have a cytochrome c1:c:aa3 ratio of 0.65:1.0:1.0 as isolated; Keilin-Hartree submitochondrial particles ahve a ratio of 0.65:0.4:1.0. More than 50% of the submitochondrial particle membrane is in the 'inverted' configuration, shielding the catalytically active cytochrome c. The 'endogenous' cytochrome c of particles turns over at a maximal rate between 450 and 550 s-1 during the oxidation of succinate or ascorbate plus TMPD; the maximal turnover rate for cytochrome c in mitochondria is 300-400 s-1, at 28 degrees-30 degrees C, pH 7.4. 2. Ascorbate plus N,N,N',N'-tetramethyl-p-phenylene diamine added to antimycin-treated particles induces anomalous absorption increases between 555 and 565 nm during the aerobic steady state, which disappear upon anaerobiosis; succinate addition abolishes this cycle and permits the partial resolution of cytochrome c1 and cytochrome c steady states at 552.5-547 nm and 550-556.5 nm, respectively. 3. Cytochrome c1 is rather more reduced than cytochrome c during the oxidation of succinate and of ascorbate + N,N,N',N'-tetramethyl-p-phenylene diamine in both mitochondria and submitochondrial particles; a near equilibrium condition exists between cytochromes c1 and c in the aerobic steady state, with a rate constant for the c1 leads to c reduction step greater than 10(3) s-1. 4. The greater apparent response of the c/aa3 electron transfer step to salts, the hyperbolic inhibition of succinate oxidation by azide and cyanide, and the kinetic behaviour of the succinate-cytochrome c reductase system, are all explicable in terms of a near-equilibrium condition prevailing at the c1/c step. Endogenous cytochrome c of mitochondria and submitochondrial particles is apparently largely bound to cytochrome aa3 units in situ. Cytochrome c1 can either reduce the cytochrome c-cytochrome aa3 complex directly, or requires only a small extra amount of cytochrome c to carry the full electron transfer flux.
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PMID:Catalytic activity of cytochromes c and c1 in mitochondria and submitochondrial particles. 17 75

We have examined the steady-state redox behavior of cytochrome c (Fec), Fea, and CuA of cytochrome c oxidase during steady-state turnover in intact rat liver mitochondria under coupled and uncoupled conditions. Ascorbate was used as the reductant and TMPD (N,N,N',N'-tetramethyl-1,4-phenylenediamine) as the redox mediator. After elimination of spectroscopic interference from the oxidized form of TMPD, we found that Fea remains significantly more oxidized than previously thought. During coupled turnover, CuA always appears to be close to redox equilibrium with Fec. By increasing the amount of TMPD, both centers can be driven to fairly high levels of reduction while Fea remains relatively oxidized. The reduction level at Fea is close to a linear function of the enzyme turnover rate, but the levels at Fec and CuA do not keep pace with enzyme turnover. This behavior can be explained in terms of a redox equilibrium among Fec, CuA, and Fea, where Fea is the electron donor to the oxygen reduction site, but only if Fea has an effective Em (redox midpoint potential) of 195 mV. This is too low to be accounted for on the basis of nonturnover measurements and the effects of the membrane potential. However, if there is no equilibrium, the internal CuA----Fea electron-transfer rate constant must be slow in the time average (about 200 s-1). Other factors which might contribute to such a low Em are discussed. In the presence of uncoupler, this situation changes dramatically. Both Fec and CuA are much less reduced; within the resolution of our measurements (about 10%), we were unable to measure any reduction of CuA. Fea and CuA remain too oxidized to be in redox equilibrium with Fec during steady-state turnover. Furthermore, our results indicate that, in the uncoupled system, the (time-averaged) internal electron-transfer rate constants in cytochrome oxidase must be of the order of 2500 s-1 or higher. When turnover is slowed by azide, the relative redox levels at Fea and Fec are much closer to those predicted from nonturnover measurements. In presence of uncouplers, Fea is always more reduced than Fec, but in the absence of uncouplers, the two centers track together. Unlike the uninhibited, coupled system, the redox behavior here is consistent with the known effect of the electrical membrane potential on electron distribution in the enzyme. Interestingly, in these circumstances (azide and uncoupler present), Fea behaves as if it were no longer the kinetically controlling electron donor to the bimetallic center.
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PMID:Steady-state redox behavior of cytochrome c, cytochrome a, and CuA of cytochrome c oxidase in intact rat liver mitochondria. 184 62

The ability of adrenergic agents to promote the differentiation and especially the mitochondriogenesis of brown fat precursor cells, grown in culture, was investigated. These cells begin to differentiate during the days preceding confluence. We found here that, already during the early growth phase, the cultures (essentially precursor cells and preadipocytes at this stage) show increased cyclic AMP (cAMP) levels when acutely stimulated with norepinephrine (NE). The cultured cells were therefore chronically treated with NE up to the time of confluence, and their cytochrome-c oxidase activity was measured as an index of mitochondriogenesis. Chronic NE treatment resulted in an increased cytochrome-c oxidase activity of the cells at confluence. This effect was reproduced by selective activation of adenylate cyclase with cholera toxin, suggesting that the NE effect was exerted through an increase in cAMP. Ascorbate (added with NE as an antioxidant) had in itself a positive effect, both on final cell number and on cytochrome-c oxidase activity. It is concluded that NE, working through beta-adrenergic receptors, can stimulate mitochondriogenesis in brown fat cells through a direct effect on the cells, in accordance with the suggestion (based on in vivo experiments) that NE accelerates, rather than initiates, the differentiation process.
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PMID:Noradrenergic stimulation of mitochondriogenesis in brown adipocytes differentiating in culture. 282

A mitochondrial preparation from duck adrenal gland was used, under aerobic conditions, to show that the oxygen requirement for the last step of aldosterone biosynthesis (transformation of 18-hydroxycorticosterone into aldosterone) is at the cytochrome P-450 level only. Vitamin C and tetramethyl-p-phenylene-diamine (TMPD) were used to increase oxygen consumption at the cytochrome a3 level, thereby decreasing its availability to cytochrome P-450. The vitamin C plus TMPD system acts as an 'oxygen trap'. Results show that despite reducing equivalents provided by L-malate, vitamin C plus TMPD strongly inhibits aldosterone biosynthesis from 18-hydroxycorticosterone (89%). Moreover, we used KCN in order to block oxygen consumption, even in the presence of vitamin C plus TMPD. Under these conditions, the inhibition of aldosterone biosynthesis from 18-hydroxycorticosterone is reduced by 51%. The reversal of this inhibition by KCN was evident but only partial. According to polarographic and electron microscopy studies, the reversal of inhibition can only be explained by an increased availability of oxygen at the cytochrome P-450 level. Experiments performed under aerobic conditions, without a nitrogen atmosphere, show that oxygen is required in the transformation of 18-hydroxycorticosterone into aldosterone, at the cytochrome P-450 level. This suggests that a classical hydroxylating mechanism is involved.
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PMID:Stimulation of oxygen consumption at the cytochrome A3 level inhibits aldosterone biosynthesis from 18-hydroxycorticosterone. 302 Dec 36

A delay in the onset of accumulation of methylene hexadecanoic acid could be engendered in Pseudomonas denitrificans growing under limited oxygen conditions when the concentration of citrate but not the concentration of succinate in the medium was increased from 0.1 to 0.5%. Ascorbate, which specifically reduced a cytochrome component possessing a maximum absorbance at 551 nm, partially inhibited the accumulation of methylene hexadecanoic acid under conditions which otherwise led to maximal production. Limiting terminal cytochrome oxidase activity by controlling the oxygen supply, or by the use of low concentrations of the oxidase inhibitors cyanide or azide also prevented the accumulation of the fatty acid regardless of the nature or concentration of carbon source in the medium. Measurement of the levels of ATP, NAD and NADH as well as the steady state of reduction of respiratory components in vivo showed that the onset of accumulation of methylene hexadecanoic acid could be specifically correlated with the state of reduction of respiratory components. The uniqueness of succinate respiration in promoting the synthesis of cyclopropane synthetase (unsaturated-phospholipid methyltransferase (EC 2.1.1.16) under limited oxygen conditions could therefore be assigned to the high degree of oxidation of respiratory components observed under this condition.
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PMID:Studies on cyclopropane fatty acid synthesis. Correlation between the state of reduction of respiratory components and the accumulation of methylene hexadecanoic acid by Pseudomonas denitrificans. 728 25

L-3,4-Dihydroxyphenylalanine (L-dopa) is toxic for human neuroblastoma cells NB69 and its toxicity is related to several mechanisms including quinone formation and enhanced production of free radicals related to the metabolism of dopamine via monoamine oxidase type B. We studied the effect of L-DOPA on activities of enzyme complexes in the electron transport chain (ETC) in homogenate preparations from the human neuroblastoma cell line NB69. As a preliminary step we compared the activity of ETC in cellular homogenates with that of purified mitochondria from NB69 cells and rat brain. Specific activities for complex I, complex II-III, and complex IV in NB69 cells were, respectively, 65, 96, and 32% of those in brain mitochondria. Complex I activity was inhibited in a dose-dependent way by 1-methyl-4-phenylpyridinium ion with an EC50 of approximately 150 microM. Treatment with 0.25 mM L-dopa for 5 days reduces complex IV activity to 74% of control values but does not change either complex I or citrate synthase. Ascorbic acid (1 mM), which protects NB69 cells from L-dopa-induced neurotoxicity, increases complex IV activity to 133% of the control and does not change other ETC complexes. Ascorbic acid also reverses L-dopa-induced reduction of complex IV activity in NB69 cells. This observation might indicate that the protection observed with ascorbic acid is related to complex IV activation. In vitro incubation with L-dopa (0.125-4 mM) for 2 min produced a dose-dependent reduction of complex IV without change in complex I and II-III activities.
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PMID:L-dopa inhibits complex IV of the electron transport chain in catecholamine-rich human neuroblastoma NB69 cells. 783 50

Growing OF1 mice were treated on a short-term basis with ad libitum, caloric-restricted, or carbohydrate-restricted diets, maintaining the same intake of vitamins and minerals in the three groups. Caloric intake was 60% of controls both in the caloric-restricted and in the carbohydrate-restricted groups. Neither global nor carbohydrate restriction changed liver superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, cytochrome oxidase, GSH, uric acid, or malondialdehyde (HPLC). Ascorbate was decreased in both restricted groups. Carbohydrate restriction, but not caloric restriction, increased unsaturation indexes of fatty acids in all lipid classes analyzed and increased sensitivity to peroxidation by one order of magnitude. It is concluded that short-term caloric restriction does not seem to increase antioxidants and decrease peroxidation in the mouse liver whereas long-term restriction can avoid decreases of antioxidants and increases of peroxidation during aging. Our experiments support the prevailing view that the caloric restriction phenomenon is due to a reduction in calories themselves instead of to a reduction in carbohydrates. This last manipulation strongly increases sensitivity to peroxidative damage in the liver. The results show that in vivo fatty acid unsaturation is a main factor in determining the sensitivity to lipid peroxidation.
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PMID:Relationship between lipid peroxidation, fatty acid composition, and ascorbic acid in the liver during carbohydrate and caloric restriction in mice. 821 21

The pathophysiological link between work-related exposures and neck myalgia remains a puzzle. According to the hypothesis presented here, neck myalgia is evoked when low-level contractions in the trapezius muscle are combined with sympathetic vasoconstriction due to psychological stress or prolonged head-down neck flexion at work. These ischemic contractions increase nitric oxide/oxygen concentration ratio in the muscle fibres, enhancing herewith the reversible inhibition of mitochondrial cytochrome oxidase by nitric oxide. The result is depletion of adenosine triphosphate, which elicits production/efflux of lactic acid, in turn activating and sensitising proton-sensitive nociceptive fibres in the connective tissue, causing myalgic pain and tenderness. High estrogen-level, which gives a high expression of nitric oxide synthase in the muscle, accentuates the situation. During episodes of sustained inhibition of cytochrome oxidase by nitric oxide, peroxynitrite may be produced and cause irreversible inactivation of several enzymes in the mitochondrial electron-carrier chain. With repeated episodes, an increasing part of the enzymatic capacity for cellular respiration is inactivated. Even if this process only takes place within a small portion of the muscle fibres, it may contribute to frequent exacerbations of pain. Effects of peroxinitrite may also explain the mitochondrial abnormalities found in the trapezius muscle of many neck myalgia patients. Adrenergic antagonists and nitric oxide synthase inhibitors could reduce symptoms. Ascorbic acid, alpha tocopherol, and flavonoids, which are safe and effective scavengers of peroxynitrite, could prevent chronicity. The most effective non-pharmacological measure may be to reduce exposure to prolonged head-down neck flexions and psychosocial stress at work.
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PMID:Linking work factors to neck myalgia: the nitric oxide/oxygen ratio hypothesis. 1508 96

Ascorbic acid oxidase activity in Myrothecium verrucaria extracts resulted in O(2) uptake exceeding 0.5 mole per mole of ascorbic acid and in CO(2) evolution. Measurement of oxidized ascorbic acid at completion of the reaction demonstrated that an average of 10% of the oxidized product disappeared. A comparison of the gas exchange data with the amount of ascorbic acid not accounted for indicated that the reaction could not be explained by independent oxidase and oxygenase systems. Chromatographic examination of the reaction mixtures identified l-threonic acid. Experiments with ascorbic acid-1-(14)C showed that C-1 was partially decarboxylated during the oxidation. Test of the fungal extracts for enzymes that might explain the deviation from expected stoichiometry showed that phenolase, glutathione reductase, cytochrome oxidase, peroxidase and oxalic decarboxylase were not involved. Addition of azide in concentrations sufficient to block catalase increased excess O(2) consumption about 65%. No enzymes were found that could directly attack oxidized ascorbic acid. H(2)O(2) accumulated during oxidation in azide-blocked systems.The O(2) excess could be explained by assuming the enzyme had peroxidative capacity on a reductant other than ascorbic acid. An intermediate of ascorbic acid oxidation appeared to function as the substrate yielding CO(2) and l-threonic acid on degradation. The increase in excess O(2) utilized in azide-blocked systems and the H(2)O(2) accumulation also were explained by the proposed scheme.Another interpretation would involve production of free radicals during ascorbic acid oxidation. Evidence for this was the ability of extracts to oxidize DPNH in the presence of ascorbic acid. Oxygen radicals formed in such reactions were considered possible agents of degradation of ascorbic acid.
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PMID:Reaction Properties of the Ascorbic Acid Oxidase from Myrothecium verrucaria. 1665 40


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