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)

In stopped-flow experiments in which oxidized cytochrome c oxidase was mixed with ferrocytochrome c in the presence of a range of oxygen concentrations and in the absence and presence of cyanide, a fast phase, reflecting a rapid approach to an equilibrium, was observed. Within this phase, one or two molecules of ferrocytochrome were oxidized per haem group of cytochrome a, depending on the concentration of ferrocytochrome c used. The reasons for this are discussed in terms of a mechanism in which all electrons enter through cytochrome a, which, in turn, is in rapid equilibrium with a second site, identified with 'visible' copper (830 nm-absorbing) Cud (Beinert et al., 1971). The value of the bimolecular rate constant for the reaction between cytochromes c2+ and a3+ was between 10(6) and 10(7) M(-1)-S(-1); some variability from preparation to preparation was observed. At high ferrocytochrome c concentrations, the initial reaction of cytochrome c2+ with cytochrome a3+ could be isolated from the reaction involving the 'visible' copper and the stoicheiometry was found to approach one molecule of cytochrome c2+ oxidized for each molecule of cytochrome a3+ reduced. At low ferrocytochrome c concentrations, however, both sites (i.e. cytochrome a and Cud) were reduced simultaneously and the stoicheiometry of the initial reaction was closer to two molecules of cytochrome c2+ oxidized per molecule of cytochrome a reduced. The bleaching of the 830 nm band lagged behind or was simultaneous with the formation of the 605 nm band and does not depend on the cytochrome c concentration, whereas the extinction at the steady-state does. The time-course of the return of the 830 nm-absorbing species is much faster than the bleaching of the 605 nm-absorbing component, and parallels that of the turnover phase of cytochrome c2+ oxidation. Additions of cyanide to the oxidase preparations had no effect on the observed stoicheiometry or kinetics of the reduction of cytochrome a and 'visible' copper, but inhibited electron transfer to the other two sites, cytochrome a3 and the undetectable copper, Cuu.
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PMID:Kinetic studies on the reaction between cytochrome c oxidase and ferrocytochrome c. 16 79

1) Cells of Saccharomyces cerevisiae have been analysed by single and double-bean spectroscopy. Evidence is given for two components of cytochrome c oxidase in the alpha-region of their absorption spectrum. A rapidly reduceable component with a maximum at 600 nm and a slowly reduceable component with a maximum at 604 nm contribute about equal amounts to the total alpha-absorption of cytochrome c oxidase. 2) The component absorbing at 600 nm was identified as the high-potential component with a redox potential of 340 - 355mV, and the 604-nm component as the low-potential component of cytochrome c oxidase with redox potential of 180 - 190 mV. 3) Both components can be characterized by analysing the reduction kinetics in the presence of carbon monoxide. In the presence of saturating concentrations of carbon monoxide, an oxygen pulse leads to a rapid oxidation and subsequent reduction of cytochrome c oxidase, but the rapid reduction phase at 600 nm completely disappears, demonstrating its identity with cytochrome a3, which, being liganded by carbon monoxide in its reduced state, cannot react any more. The component which becomes oxidized and later reduced in the presence of carbon monoxide -- by definition cytochrome a -- has an absorption maximum at 604 nm. 4) The total extinction change at 604 nm in the presence of carbon monoxide is nearly as high as in its absence, but the reduction occurs in two phases and only the second phase, which contributes 50 - 60% to the total absorbance, corresponds in redox potential and kinetic properties to cytochrome a. Because the redox potential of the first reduction phase is very close to that of the low-potential copper atom of cytochrome c oxidase, it is concluded that the apparent increase in the extinction coefficient of cytochrome a in the presence of carbon monoxide is the result of a strong interaction between the ligand fields of cytochrome a and copper, induced by the binding of carbon monoxide to reduced cytochrome a3.
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PMID:Identification of cytochrome a and a3 in yeast cells. 17 24

The effects of hydroxycobalamin on inhibition of cytochrome c oxidase by cyanida in isolated intact mitochondria were studied. No effect of hydroxycobalamin (HCo) and cyanocobalamin (CNCo) was observed on normal mitochondria. When mitochondria inhibited by cyanida were treated with HCo the respiration with ADP, the respiration after ADP and respiratory coefficient (RC) were increased. No effect was observed with CNCo. Difference spectra of the effect of HCo on the inhibition of cytochrome c oxidase by cyanida and azide in isolated intact mitochondria were recorded using a split beam spectrophotometer. The results presented herein suggest that HCo reverses the cyanide inhibition because part of cytochrome a3 is free from cyanide as a consequence of dissociation of the complex, resulting in CNCo formation. If this reaction continues to occur together with a probable by pass between cytochrome a and oxygen throught the HCo (which was not transformed in CNCo), oxygen consumption and most of the respiratory chain will be maitened in the active state.
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PMID:Effect of hydroxycobalamin on the inhibition of cytochrome c oxidase by cyanide. I - In intact mitochondria. 17 99

The basic protein protamine is found to be a potent inhibitor of mitochondrial cytochrome c oxidase, while the oxidase activity of the "inside out" submitochondrial particles is only slightly affected by this polycation. The site of inhibition of mitochondrial respiration by protamine is localized between cytochromes c and a, protamine combining with cytochrome oxidase competitively to cytochrome, c, Ki=2,5 x 10(-6) M. The data obtained suggest that it is the outer side of the mitochondrial membrane where oxidation of cytochrome c by cytochrome a occurs.
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PMID:[Protamine as a specific inhibitor of electron transport between cytochromes c and a on the outer surface of the mitochondrial membrane]. 17 21

Inorganic lead, added to the diet of suckling rat in high doses, produces an encephalopathy similar to that seen in the immature human. Pathologic changes of edema and hemorrhage are seen earliest and are most prominent in the cerebellum. In this study, we measured respiration in cerebral hemisphere and cerebellar mitochondria isolated from led-fed and age-matched normal rat pups. Lactating mothers were begun on ad libitum feedins containing 4% lead carbonate when their pups were 2 weeks old. Mitochondria were isolated by differential centrifugation. Oxygen consumption was measured polarographically, NAD-linked respiration was measured with oxidation of the substrate pair, glutamate and malate. Cytochrome oxidase (cytochrome c oxidase, EC. 1.9.3.1) activity was measured in the presence of tetramethyl-p-phenylenediamine dihydrochloride (TMPD) and ascorbate. Within 2 days of starting lead feedings, rat pups showed a significant loss in body weight (P less than 0.02) and, after 1 week, a significant loss in cerebral hemisphere wet weight (P less than 0.01) compared with controls. Overt encephalopathy appeared in pups from two of nine litters receiving lead feedings for 1 week and in half of the litters after 2 weeks of feedings. None of the lead-fed mothers developed encephalopathic signs. With oxidation of the NAD-linked substrate pair, there was a progressive decrease, relative to controls, in ADP/O ratios in both cerebellar and cerebral mitochondria from lead-fed animals. After 2 weeks these differences were significant in mitochondria from both regions (cerebellum, P less than 0.02; cerebrum, P less than 0.005). Respiratory control ratios were significantly lower in cerebellar mitochondria from lead-fed rats within 2 days of beginning feedings (P less than 0.02) and in mitochondria from both regions after 2 weeks of lead feedings (cerebellum, P less than 0.01; cerebrum, P less than 0.05). The decrease in control ratios in cerebellar mitochondria from animals receivint lead feedings for 1 week or less was due to a small decrease in state 3 respiration and a large, but inconsistent, increase in state 4 respiration. The decrease in control ratios in both cerebellar and cerebral hemisphere mitochondria after 2 weeks of lead feedings was due to a marked inhibition of state 3 respiration, relative to controls (cerebellum, P less than 0.01; cerebral hemisphers, P less than 0.05). In cerebellar mitochondria from lead-fed animals, cytochrome oxidase activity showed similar changes compared with controls: a highly significant (P less than 0.001) increase within 2 days of beginning feedings and a significant (P less than 0.01) decrease after 2 weeks of feedings.
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PMID:Early effects of inorganic lead on immature rat brain mitochondrial respiration. 17 53

Attempts to rationalize the kinetics of cytochrome c oxidation catalyzed by solubilized mitochondrial cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) have been based on assumptions of productive complex formation (Michaelis-Menten approach). However, the range of substrate concentrations used has not, in general, been sufficient to establish a general rate equation. Data adequate to derive such a rate expression are presented, as well as a method for estimation of constants which appear in the rate law deduced and reported herein. It is shown that either of two types of mechanisms, one assuming productive complex formation, as opposed to the other postulating dead-end complex formation, accurately predict the rate equation as deduced from experiment.
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PMID:Oxidation of ferrocytochrome c by mitochondrial cytochrome c oxidase. 17 95

1. The major EPR signals from native and cytochrome c-reduced beef heart cytochrome c oxidase (EC 1.9.3.1) are characterized with respect to resonance parameters, number of components and total integrated intensity. A mistake in all earlier integrations and simulations of very anisotropic EPR signals is pointed out. 2. The so-called Cu2+ signal is found to contain at least three components, one "inactive" form and two nearly similar active forms. One of the latter forms, corresponding to about 20% of the total EPR detectable Cu, has not been observed earlier and can only be resolved in 35 GHz spectra. It is not reduced by cytochrome c and is thought to reflect some kind of inhomogeneity in the enzyme preparation. The 35 GHz spectrum of the cytochrome c reducible component shows a rhombic splitting and can be well simulated with g-values 2.18, 2.03 and 1.99. The origin of such a unique type of Cu2+ spectrum is discussed. 3. The low-spin heme signal in the oxidized enzyme (g = 3.03, 2.21, 1.45) is found to correspond closely to one heme and shows no signs of interaction with other paramagnetic centres. 4. The high-spin heme signals appearing in partly reduced oxidase are found to consist of at least three species, one axial and two rhombic types. An integration procedure is described that allows the determination of the total integral intensity of high-spin heme EPR signals only by considering the g = 6 part of the signals. In a titration with ascorbate and cytochrome c the maximum intensity of the g = 6 species corresponds to 23% of the enzyme concentration.
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PMID:EPR signals from cytochrome c oxidase. 17 42

Dynamics of cytochrome oxidase inactivation was studied in ischemic liver tissue using tetramethyl paraphenylene diamine (TMPD-oxidase) and cytochrome c (cytochrome c oxidase) as substrates. The cytochrome c ovidase activity was determined in presence of low concentrations (0.03%) of Triton X-100 (the total activity) and without the detergent (the free activity). Within 60 min after the restriction of oxygen supply to the liver tissue TMPD-oxidase was inactivated almost completely, at the same time cytochrome c oxidase maintained its activity. The free enzymatic activity became equal to the total activity; this phenomenon demonstrated an increased permeability of the external mitochondrial membrane for cytochrome c. The decrease in the TMPD-oxidase activity was considered to be due to the cytochrome c solubilization. This assumption was supported by the experiments, in which the addition of cytochrome c into the incubation mixture restored the enzymatic activity to the initial level. Hypotonic solutions and treatment of mitochondria with phospholipase A were found to simulate the impairment of the organelles in ischemic liver tissue. Increased peroxidation of unsaturated fatty acids in presence of ascorbic acid and ferrous ions was not accompanied by solubilization of cytochrome c.
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PMID:[Solubilization of cytochrome c in ischemic liver tissue]. 17 68

The effects of hydroxycobalamin on inhibition of the isolated cytochrome c oxidase (EC 1.9.3.1) by cyanide were studied. No effect of hydroxycobalamin (HCo) and cyanocobalamin (CNCo) was observed on isolated cytochrome c oxidase. When cytochrome c oxidase inhibited by cyanide was treated with HCo the reversal of inhibition could be observed through the spectrum of cytochrome c oxidase without reversal of activity; CNCo had no effect. The treatment of cyano-cytochrome c oxidase with HCo suggests that there is the formation of cobalamin-cytochrome c oxidase complex plus CNCo, and it is possible that complex formation would be between the cobalt of cobalamin and proteic part of cytochrome c oxidase.
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PMID:Effect of hydroxycobalamin on the inhibition of cytochrome c oxidase by cyanide. II - In isolated cytochrome C oxidase. 18 May 78

A model is proposed for the active center of cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) in which cytochrome a is a low-spin ferrihemoprotein and cytochrome a3 is a high-spin ferrihemoprotein antiferromagnetically coupled to one of the two Cu2+ ions present in the enzyme. It is further proposed that reduction is accompanied by a conformational change in the enzyme thus exposing the sixth coordination site of cytochrome a3 to ligands. With this model it is possible to account for a variety of outstanding observations including the results of magnetic circular dichroism, Mossbauer, and electron paramagnetic resonance spectroscopies, as well as magnetic susceptibility measurements.
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PMID:A model for cytochrome oxidase. 18 47


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