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)

Oxidation of exogenous NADH in mitochondria isolated from wild type and mi-1 mutant of Neurospora crassa decreases rapidly in vitro. In mi-1 mutant mitochondria the inactivation concerns the alternate pathway of oxidation whereas in the wild type it involves an unknown component of the respiratory chain. The activity of the primary NADH dehydrogenase is constant within the time of the experiments (2-4 h). NADH oxidase is not inactivated if oxygen is removed from the incubation medium by nitrogen bubbling. Succinate oxidase does not show any remarkable changes in activity within 2-3 h. In fresh mitochondria of the mi-1 mutant reduced ubiquinone is completely reoxidized by cytochrome oxidase but only 80% reoxidized by the alternate oxidase. In aged mitochondria of the mi-1 mutant in the presence of cyanide, ubiquinone is reduced to the level characteristic for fresh mitochondria in which respiration is completely inhibited by cyanide plus salicylhydroxamic acid. In these mitochondria the reoxidation of the reduced ubiquinone proceeds only via the cytochrome pathway. It is supposed that a labile component(s) of the respiratory chain present in the mi-1 mutant and the wild type mitochondria may, in mi-1 mutant, act as an alternate oxidase.
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PMID:Disappearance of the cyanide-insensitive pathway of oxidation in mitochondria of MI-1 mutant of Neurospora crassa in vitro. 20 34

Cytochrome oxidase forms two distinctive compounds with oxygen at --105 and --90 degrees C, one appears to be oxycytochrome oxidase (Compound A) and the other peroxycytochrome oxidase (Compound B). The functional role of compound B in the oxidation of cytochrome c has been examined in a variety of mitochondrial preparations. The rate and the extent of the reaction have been found to be dependent upon the presence of a fluid phase in the vicinity of the site of the reaction of cytochrome c and cytochrome oxidase. The kinetics of cytochrome c oxidation and of the slowly reacting component of cytochrome oxidase are found to be linked to one another even in cytochrome c depleted preparations, but under appropriate conditions, especially low temperatures, the oxidation of cytochrome c precedes that of this component of cytochrome oxidase. Based upon the identification of the slowly reacting components of cytochrome oxidase with cytochrome c, various mechanisms are considered which allow cytochrome c to be oxidized without the intervention of cytochrome a at very low temperatures, and tunneling seems an appropriate mechanism.
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PMID:Cytochrome c-cytochrome oxidase interaction at subzero temperatures. 20 1

The interrelation of neuronal function and oxidative metabolism of the brain is most incisively studied by optical techniques in vivo. When O2 becomes limited the respiratory chain becomes reduced, extracellular potassium activity is increased, the EEG is depressed and excitability declines, all as expected. Under mildly hyperoxic conditions however, the opposite responses occur, which indicate an absence of a critical tissue Po2 and a continuum of dependence on the O2 concentration, including levels well above the limits for maximal activity of the respiratory chain in isolated mitochondria in vivo. The unexpectedly high steady state of reduction of cytochrome a, a3 provides the basis for a new hypothesis of an extra energy conservation site between cytochrome a3 and O2 and leads to a consideration of a reaction mechanism of O2 with four electrons and four H+ ions occurring at an enzymically active centre of cytochrome a, a3. A special function of the cytochrome a, a3 complex is implied in regulating cellular K+ transport and thus excitability.
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PMID:Behaviour of the mitochondrial respiratory chain in vivo. 20 22

The reduction of cytochrome c by succinate-cytochrome c reductase was studied at very low cytochrome c concentrations where the reaction between cytochrome c1 and cytochrome c was rate limiting. The rate constant for the reaction was found to be independent of ionic strength up to 0.1 M chloride, and to decrease rapidly at higher ionic strength, suggesting that the interaction between cytochrome c1 and cytochrome c was primarily electrostatic. The reaction rates of cytochrome c derivatives modified at single lysine residues to form trifluoroacetylated or trifluoromethylphenylcarbamylated cytochromes c were studied to determine the role of individual lysines in the reaction. None of the modifications affected the reaction at low ionic strength, but at higher ionic strength the reaction rate was substantially decreased by modification of those lysines surrounding the heme crevice, lysine-8, -13, -27, -72, and -79. Modification of lysine-22, -25, -55, -99, and -100 had no effect on the rate. These results indicate that the binding site on cytochrome c for cytochrome c1 overlaps considerably with that for cytochrome oxidase, suggesting that cytochrome c might undergo some type of rotational diffusion during the electron-transport process.
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PMID:Effect of specific lysine modification on the reduction of cytochrome c by succinate-cytochrome c reductase. 20 18

1. The membrane-bound succinoxidase of Escherichia coli was fractionated with deoxycholate into three soluble components, viz. succinate dehydrogenase.cytochrome b1 complex, cytochrome oxidase complex, and a factor identified as a phospholipid-containing component. 2. The dehydrogenase and cytochrome oxidase complexes were partially purified by filtration on Amicon membranes, Sepharose 4B chromatography, and sucrose gradient centrifugation. 3. Reconstitution of membranous succinoxidase, which catalyzes the oxidation of succinate by molecular oxygen by an integrated CN(-)-sensitive pathway, was achieved by mixing the soluble succinate dehydrogenase.cytochrome b1 complex with the soluble cytochrome oxidase complex in the presence of deoxycholate and then removing the detergent by gel filtration on Sephadex G-75. The phospholipid-containing factor stimulated the formation of succinoxidase by about 100% over that observed with the two complexes. 4. Isopycnic sucrose gradient centrifugation of succinate dehydrogenase.cytochrome b1 complex, cytochrome oxidase, and the reconstituted succinoxidase gave buoyant densities (p value) as 1.167, 1.229, and 1.194, respectively. 5. Electron microscopic evidence is presented for the vesicular nature of the reconstituted succinoxidase.
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PMID:Reconstitution of escherichia coli succinoxidase from soluble components. 21 41

The temperature dependence of the paramagnetic susceptibility of cytochrome oxidase and some of its derivatives has been measured from 7 to 200 K. The results obtained for the fully oxidized (resting) enzyme correspond exactly to the requirements of the model recently proposed by Palmer et al. (Palmer, G., Babcock, G. T., and Vickery, L. E. (1976) Proc. Natl. Acad. Sci. U. S. A. 73, 2206-2210) in which the enzyme possesses two magnetically isolated spin S = 1/2 centers and a spin-coupled S = 2 center. The S = 2 center paramagnetism has been interpreted as arising from a [cytochrome a33+(S = 5/2)--Cuu2+(S = 1/2)] antiferromagnetically coupled iron.copper binuclear complex of total spin S = 2 with -J greater than or equal to 200 cm-1. In addition, the wide temperature range used in the present studies has permitted an analysis of present and other available data (T less than 4K measurements) which readily accommodates results from this and other laboratories (Moss, T.H., Shapiro, E., King, T.E., Beinert, H., and Hartzell, C. R. (1978) J. Biol. Chem 253, 8072-8073) so that a fully consistent picture of the magnetic centers in cytochrome oxidase now appears to be available. Furthermore, anomalous magnetic behavior for the oxidized enzyme.cyanide complex has been interpreted in terms of an antiferromagnetic exchange interaction operating in the binuclear complex [cytochrome a33+.CN-(S = 1/2)--Cuu2+(S = 1/2)] with -J congruent to 40 cm-1. A structural model for the [cytochrome a3(3+)-bridge-CUu2+] center is advanced in which an imidazolate ion serves as the bridging ligand in a manner similar to that found in superoxide dismutase.
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PMID:Electronic state of heme in cytochrome oxidase III. The magnetic susceptibility of beef heart cytochrome oxidase and some of its derivatives from 7-200 K. Direct evidence for an antiferromagnetically coupled Fe (III)/Cu (II) pair. 21 27

The energy relationships between cytosolic and mitochondrial metabolism were studied in the hearts from euthyroid, hypothyroid, and hyperthyroid rats. Isolated mitochondria showed high respiratory control ratios and impermeability to exogenous NADH. Hypo- and hyperthyroidism, respectively, resulted in lower and higher contents of both cytochromes per mitochondrion and mitochondrial protein per gram of wet weight of heart without changes in the ratio of cytochrome c to cytochrome aa3. In isolated perfused heart, the hyperthyroid state led to an increase in work rate and thereby an elevation of Vo2, which resulted in an increase oxidation-reduction turnover number for the cytochromes. An agreement was found between [ATP]/[ADP][Pi] of cytosolic free adenine nucleotides and the value calculated from a mathematical model of mitochondrial respiration. This implies that mitochondrial respiration is controlled at the cytochrome oxidase reaction and that oxidative phosphorylation in intact tissue is tightly coupled irrespective of thyroid state. It is concluded that thyroid hormone causes an increase in the mitochondrial mass, mitochondrial cytochrome content, and respiratory rate, and consequently expands the capacity of oxidative metabolism without an uncoupling effect on oxidative phosphorylation.
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PMID:Evaluation of oxidative phosphorylation in hearts from euthyroid, hypothyroid, and hyperthyroid rats. 21 35

The EPR absorption properties of the hemes of cytochrome oxidase and their liganded derivatives were examined in oriented multilayers from isolated oxidase, mitochondrial membranes and membrane fragments of a bacterium, Paracoccus denitrificans. The hemes of the oxidase in all the systems investigated were oriented normal to the plane of the multilayers. The directions of the g signals corresponding to the gx and gy axes of the g tensor were found to be different in low-spin ferric heme in fully oxidized oxidase and in half-reduced liganded oxidase. It is suggested that this different orientation of gx and gy in fully oxidized oxidase and half-reduced liganded oxidase arises because the respective EPR signals belong to two different hemes, those of cytochrome a and a3.
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PMID:Studies of the orientation of the mitochondrial redox carriers. III. Orientation of the gx and gy axes of the hemes of cytochrome oxidase with respect to the plane of the membrane in oriented membrane multilayers. 21 1

The mitochondria of the cyt-2-1, cya-3-16, cya-4-23 and 299-1 nuclear mutants and the [mi-3] and [exn-5] cytoplasmic mutants of Neurospora crassa are deficient in cytochrome aa3, while the cyb-1-1 and cyb-2-1 mutants have mitochondrial b-cytochrome deficiencies. However, the mitochondria from cyb-1-1 cyt-2-1, cyb-1-1 [mi-3] and cyb-2-1 [mi-3] double mutants contain 30% to 50% of the amount of cytochrome aa3 that is present in mitochondria from wild-type; i.e. cyb-1-1 and cyb-2-2 act as suppressors of the cytochrome aa3 deficiency phenotypes that are associated with cyt-2-1 and [mi-3] mutations. The production of cytochrome aa3 can be induced in cyt-2-1 and [mi-3] by growing cells in medium containing antimycin A, an inhibitor of electron transport in the cytochrome bc1 segment of the mitochondrial electrontransport chain. Moreover, the growth of the [mi-3] mutant is strongly stimulated by low concentrations of antimycin A. The induction of cytochrome aa3 by antimycin treatments does not occur in [exn-5], cya-4-23 and 299-1 cells; but does take place in cya-3-16 cells. Although some of the seven constituent polypeptides of cytochrome aa3 are present in mitochondria of [mi-3], the holoenzyme complex is not formed in the mutant. In contrast, the mitochondria of cyb-1-1 [mi-3] and cyb-2-2 [mi-3] double mutants contain a fully assembled cytochrome oxidase complex as well as some unassembled subunit polypeptides. The observations are indicative of the existence of at least two regulatory systems controlling the production of cytochrome aa3. One of the circuits appears to control the basal or "constitutive" production of cytochrome oxidase, the other seems to coordinate the level of cytochrome aa3 with some function of the mitochondrial cytochrome bc1 complex, possibly electron transport.
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PMID:A regulatory system controlling the production of cytochrome aa3 in Neurospora crassa. 21 99

Non-invasive optical techniques were used to monitor the effects of increasing cerebral energy demand on metabolic capabilities and vascular reactivity in young and aged brain. Low level of electrical stimulation of the cortex, in both young (4--7 months) and aged (24--28 months) rat brain, were accompanied by transient oxidations of NADH and cytochrome oxidase (a,a3) as measured by microfluorometry and reflection spectrophotometry respectively. Stimulation sufficient to produce spreading cortical depression was accompanied by an oxidation of both NADH and cytochrome a,a3 in young brain together with an increase in local blood volume. There was either no change or a slight disoxygenation of hemoglobin. In aged brain, however, spreading depression was associated with an oxidation of NADH and a reduction of cytochrome a,a3 together with an increase in local blood volume and an oxygenation of hemoglobin. The present results indicate that the relationship between microcirculation and the terminal oxidase step of the respiratory chain is altered in aged brain when energy demand is high.
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PMID:Effects of age on brain oxidative metabolism in vivo. 21 92


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