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)

The structural comparison of copper-containing proteins has provided a new dimension to the relationships suggested by sequence similarities. Ryden (1988) summarized the putative relationships, suggesting that a primordial single-domain cupredoxin evolved into the multidomain copper oxidases. The structures have revealed the fact that the differences reside primarily in insertions and deletions at junctions between secondary-structure elements. The mechanism of evolution (e.g., integration of new sequences into regions not essential to the Greek key fold) remains unknown. Which of the properties of a cupredoxin fold are necessary for function is the subject of site-directed mutagenesis studies. Can two of the ligands be interchanged (e.g., the upstream histidine and partially answered by the multidomain copper oxidase structure. The Tyr-Cys-Thr sequence in plastocyanin (in which threonine is a member of the hydrogen-bonding pair) is homologous with the His-Cys-His sequence in ascorbate oxidase. In the latter electron transfer is believed to flow from the type I copper (bound by the cysteine) to the trinuclear cluster, probably via these histidine residues. Hence, one might infer that the tyrosine and threonine have some role in electron transfer. Tyr-83 has been previously implicated in NMR studies as a primary site of electron transfer. The multi-copper protein structures have revealed interesting new features. The extra coppers are bound at domain interfaces, and can be single metals or the novel trinuclear cluster, depending on the availability of liganding histidines. A structural model of ceruloplasmin suggests that it will have at least two type I sites and, possibly, a third type I site such as stellacyanin (no methionine ligand), as well as a binding site for a trinuclear cluster. The similarity of the sequences of N2O reductases and a domain of cytochrome oxidase to the sequences of proteins with known structures suggests that these, too, will have Greek key domains. Galactose oxidase and hemocyanin do not have Greek key folds in their functional domains, although each does have a Greek key domain. The need for a Greek key fold remains obscure. The apoproteins are clearly stable without metals; there are examples other than immunoglobulins of Greek key folds. So far copper seems to be found in a very limited subset of structures; other chapters in this volume show that zinc, for example, has a much wider variety of environments in proteins, as does iron. It may be that the copper-containing Greek key proteins represent a very small evolutionary niche.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Copper protein structures. 179 5

Under anaerobic circumstances in the presence of nitrate Paracoccus denitrificans is able to denitrify. The properties of the reductases involved in nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase are described. For that purpose not only the properties of the enzymes of P. denitrificans are considered but also those from Escherichia coli, Pseudomonas aeruginosa, and Pseudomonas stutzeri. Nitrate reductase consists of three subunits: the alpha subunit contains the molybdenum cofactor, the beta subunit contains the iron sulfur clusters, and the gamma subunit is a special cytochrome b. Nitrate is reduced at the cytoplasmic side of the membrane and evidence for the presence of a nitrate-nitrite antiporter is presented. Electron flow is from ubiquinol via the specific cytochrome b to the nitrate reductase. Nitrite reductase (which is identical to cytochrome cd1) and nitrous oxide reductase are periplasmic proteins. Nitric oxide reductase is a membrane-bound enzyme. The bc1 complex is involved in electron flow to these reductases and the whole reaction takes place at the periplasmic side of the membrane. It is now firmly established that NO is an obligatory intermediate between nitrite and nitrous oxide. Nitrous oxide reductase is a multi-copper protein. A large number of genes is involved in the acquisition of molybdenum and copper, the formation of the molybdenum cofactor, and the insertion of the metals. It is estimated that at least 40 genes are involved in the process of denitrification. The control of the expression of these genes in P. denitrificans is totally unknown. As an example of such complex regulatory systems the function of the fnr, narX, and narL gene products in the expression of nitrate reductase in E. coli is described. The control of the effects of oxygen on the reduction of nitrate, nitrite, and nitrous oxide are discussed. Oxygen inhibits reduction of nitrate by prevention of nitrate uptake in the cell. In the case of nitrite and nitrous oxide a competition between reductases and oxidases for a limited supply of electrons from primary dehydrogenases seems to play an important role. Under some circumstances NO formed from nitrite may inhibit oxidases, resulting in a redistribution of electron flow from oxygen to nitrite. P. denitrificans contains three main oxidases: cytochrome aa3, cytochrome o, and cytochrome co. Cytochrome o is proton translocating and receives its electrons from ubiquinol. Some properties of cytochrome co, which receives its electrons from cytochrome c, are reported.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Metabolic regulation including anaerobic metabolism in Paracoccus denitrificans. 205 Jun 53

Bovine heart submitochondrial particles (SMP) were exposed to continuous fluxes of hydroxyl radical (.OH) alone, superoxide anion radical (O2-) alone, or mixtures of .OH and O2-, by gamma radiolysis in the presence of 100% N2O (.OH exposure), 100% O2 + formate (O2- exposure), or 100% O2 alone (.OH + O2- exposure). Hydrogen peroxide effects were studied by addition of pure H2O2. NADH dehydrogenase, NADH oxidase, succinate dehydrogenase, succinate oxidase, and ATPase activities (Vmax) were rapidly inactivated by .OH (10% inactivation at 15-40 nmol of .OH/mg of SMP protein, 50-90% inactivation at 600 nmol of .OH/mg of SMP protein) and by .OH + O2- (10% inactivation at 20-80 nmol of .OH + O2-/mg of SMP protein, 45-75% inactivation at 600 nmol of .OH + O2-/mg of SMP protein). Importantly, O2- was a highly efficient inactivator of NADH dehydrogenase, NADH oxidase, and ATPase (10% inactivation at 20-50 nmol of O2-/mg of SMP protein, 40% inactivation at 600 nmol of O2-/mg of SMP protein), a mildly efficient inactivator of succinate dehydrogenase (10% inactivation at 150 nmol of O2-/mg of SMP protein, 30% inactivation at 600 nmol of O2-/mg of SMP protein), and a poor inactivator of succinate oxidase (less than 10% inactivation at 600 nmol of O2-/mg of SMP protein). H2O2 partially inactivated NADH dehydrogenase, NADH oxidase, and cytochrome oxidase, but even 10% loss of these activities required at least 500-600 nmol of H2O2/mg of SMP protein. Cytochrome oxidase activity (oxygen consumption supported by ascorbate + N,N,N',N'-tetramethyl-p-phenylenediamine) was remarkably resistant to oxidative inactivation, with less than 20% loss of activity evident even at .OH, O2-, OH + O2-, or H2O2 concentrations of 600 nmol/mg of SMP protein. Cytochrome c oxidase activity, however (oxidation of, added, ferrocytochrome c), exhibited more than a 40% inactivation at 600 nmol of .OH/mg of SMP protein. The .OH-dependent inactivations reported above were largely inhibitable by the .OH scavenger mannitol. In contrast, the O2(-)-dependent inactivations were inhibited by active superoxide dismutase, but not by denatured superoxide dismutase or catalase. Membrane lipid peroxidation was evident with .OH exposure but could be prevented by various lipid-soluble antioxidants which did not protect enzymatic activities at all.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The oxidative inactivation of mitochondrial electron transport chain components and ATPase. 216 88

Cerebral partial pressure of O2 (PO2), relative changes in the ratio of reduced/oxidized cytochrome aa3, blood flow, and the arteriovenous difference in O2 content were measured during seizures with and without pulmonary edema. Seizures were induced with bicuculline (0.2-1.2 mg/kg iv) in rats anesthetized with 70% N2O and paralyzed with curare. Briefer seizures were accompanied by increased cerebral PO2 and increased oxidation of cytochrome aa3. Lung water content and arterial O2 partial pressure (PaO2) remained normal. Longer duration seizures were also accompanied initially by increases in cerebral oxygenation. Within minutes, however, PaO2 fell from a mean of 118 to 51 mmHg, and lung water content increased from 76.2 to 83.6%. Cerebral PO2 fell but most often rose back to or above control levels, while cytochrome aa3 became markedly reduced. Simultaneously, cerebral blood flow increased more than 300% above preseizure values and O2 delivery increased more than O2 consumption. The reductive shift of cytochrome aa3 was greater than that produced by lowering PaO2 to equivalent values in seizure-free rats. The reductive shift of cytochrome aa3, despite increased O2 delivery, may be indicative of derangements in cerebral O2 diffusion or energy metabolism.
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PMID:Seizure-associated pulmonary edema and cerebral oxygenation in the rat. 355 25

Cerebral blood volume, hemoglobin saturation and the cytochrome a, a3 redox state were monitored simultaneously by using three wavelengths of light in the near infrared portion of the spectrum for transillumination of the intact skull of rats. The changes in these parameters following incomplete cerebral ischemia were assessed in Wistar and Long-Evans rats submitted to carotid ligation. Another group of Wistar rats was submitted to vertebral + carotid occlusion. The experiments, performed under N2O/O2 anesthesia, showed that in all three groups carotid occlusion induced a decrease in blood volume, Hb saturation and a reduction of cyt. a, a3. However, the cytochrome redox state tended to normalize during ischemia as a consequence of higher O2 extraction from blood. The primary finding of this study was the marked hyperoxidation of cyt. a, a3 which occurred after reestablishing of the carotid blood supply, in spite of a secondary post-ischemic hypoperfusion of the brain. Although uncoupling of oxidative phosphorylation cannot be excluded the dissociation between blood supply and metabolism could well be due to ischemia-induced hypermetabolism of the central nervous tissue. In view of the marked oxidation of cyt. a, a3 during the reperfusion period as compared with the small extent of its reduction during the ischemic episode, the data also support the hypothesis that under steady state conditions in vivo, cytochrome oxidase is mainly reduced.
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PMID:Incomplete cerebral ischemia in the rat: vascular and metabolic changes as measured by infrared transillumination in vivo. 631 78

Near-infrared spectroscopy was used to determine the effect of changes in the rate of oxygen delivery to the adult rat brain on the absolute concentrations of oxyhaemoglobin, deoxyhaemoglobin and the redox state of the CuA centre in mitochondrial cytochrome oxidase. The cytochrome oxidase detection algorithm was determined to be robust to large changes in haemoglobin oxygenation and concentration. By assuming complete haemoglobin deoxygenation and CuA reduction following mechanical ventilation on 100% N2O, the absolute concentration of oxyhaemoglobin (35 microM), deoxyhaemoglobin (27 microM) and the redox state of CuA (82% oxidized) were calculated in the normal adult brain. The mean arterial blood pressure was decreased by exsanguination. When the pressure reached 100 mmHg, haemoglobin oxygenation started to fall, but the total haemoglobin concentration and oxidized CuA levels only fell when cerebral blood volume autoregulation mechanisms failed at 50 mmHg. Haemoglobin oxygenation fell linearly with decreases in the rate of oxygen delivery to the brain, but the oxidized CuA concentration did not start to fall until this rate was 50% of normal. The results suggest that the brain maintains more than adequate oxygen delivery to mitochondria and that near-infrared spectroscopy may be a good measure of oxygen insufficiency in vivo.
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PMID:The relationship of oxygen delivery to absolute haemoglobin oxygenation and mitochondrial cytochrome oxidase redox state in the adult brain: a near-infrared spectroscopy study. 962 Aug 63

A novel, improved method for purification of nitric oxide reductase (NOR) from membranes of Paracoccus denitrificans has been developed. The purified enzyme is a cytochrome bc complex which, according to protein chemical and hydrodynamic data, contains two subunits in a 1:1 stoichiometry. The purified NorBC complex binds 0.87 g of dodecyl maltoside/g of protein and forms a dimer in solution. Similarly, it is dimeric in two-dimensional crystals. Images of these crystals have been processed at 8 A resolution in projection to the membrane. The NorB subunit is homologous to the main catalytic subunit of cytochrome oxidase and is predicted to contain the active bimetallic center in which two NO molecules are turned over to N2O. Metal analysis and heme composition implies that it binds two B-type hemes and a nonheme iron but no copper. NorC is a membrane-anchored cytochrome c. Fourier transform infrared spectroscopy shows that carbon monoxide dissociates from the reduced heme in light and associates with another metal center which is distinct from the copper site of heme/copper oxidases. Electron paramagnetic resonance spectroscopy reveals that NO binds to the reduced enzyme under turnover conditions giving rise to signals near g = 2 and g = 4. The former represents a typical nitrosyl-ferroheme signal whereas the latter is a fingerprint of a nonheme iron/NO adduct. We conclude that the active site of NOR is a dinuclear iron center.
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PMID:The active site of the bacterial nitric oxide reductase is a dinuclear iron center. 974 16

Copper deficiency myelopathy (CDM) is an increasingly recognised mimic of subacute combined degeneration (SCD) of the cord due to cobalamin (vitamin B(12)) deficiency. It has been suggested that copper deficiency induces myelopathy through dysfunction of cytochrome oxidase, which is known to be copper-dependent. However, cytochrome oxidase is not cobalamin-dependent, so this hypothesis fails to explain the phenotypic similarity between CDM and SCD. We propose that the first step in a final common pathway of CDM and SCD is dysfunction of the methylation cycle. This cycle includes both copper and cobalamin-dependent enzymes and catalyses the net transfer of a methyl group from methyltetrahydrofolate to a variety of macromolecules, including myelin proteins. Dysfunction of the cycle might therefore cause failure of myelin maintenance and ultimately myelopathy. One step of the methylation cycle is catalysed by methionine synthase, which is known to be cobalamin-dependent. Nitrous oxide specifically inhibits this enzyme by inactivating methylcobalamin, causing SCD in animals and humans. Both animal and human data suggest that methionine synthase also requires copper, implying that the enzyme may be involved in the pathogenesis of CDM. Another enzyme involved in the methylation cycle, S-adenosylhomocysteine hydrolase, may be regulated by copper. Although this enzyme is not cobalamin-dependent, its potential impairment in copper deficiency may contribute to the overall dysfunction of the methylation cycle. In cases of congenital deficiencies of methylation cycle enzymes, spinal and cerebral demyelination was observed, providing further support for a critical role of the methylation cycle in myelination. Biochemical dysfunction of the methylation cycle has been reported in HIV myelopathy, which has pathological parallels with SCD. This raises the possibility that other demyelinating myelopathies might involve an impairment of the methylation cycle. Our hypothesis could be tested by measuring CSF concentrations of methylation cycle intermediates in cases of CDM, as these reflect spinal cord tissue levels. If it were confirmed, the hypothesis would not only provide a plausible explanation for the phenotypic similarity between CDM and SCD, but might also open up further therapeutic options such as methionine and betaine supplementation.
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PMID:Copper deficiency myelopathy and subacute combined degeneration of the cord - why is the phenotype so similar? 1847 29

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