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 mechanism of electron transfer catalyzed by cytochrome oxidase was investigated by monitoring the reaction of cytochrome oxidase with cytochrome c under carefully controlled anaerobic conditions. The kinetics of the reaction were examined by varying conditions of ionic strength, inhibitor binding, and oxidation-reduction potential. An analogue of cytochrome c in which the iron atom was replaced with cobalt was used to probe the effect of redox potential on the reaction. Under conditions of low ionic strength, there is very rapid oxidation of cytochrome c and reduction of oxidase which occurs at a rate of 3 X 10(7) M-1 s-1. The number of electrons transferred exhibit a hyperbolic dependence on the concentration of cytochrome c reaching a maximum of 2 electrons transferred at the highest concentration of reduced cytochrome c employed. The total number of electrons transferred was always observed to be distributed equally between cytochrome a and a second acceptor which appears to be the associated copper center; electron transfer to cytochrome a3 did not occur in the absence of oxygen. Substitution of cytochrome c by the cobalt analogue (which represents a decrease in oxidation-reduction potential of about 400 mV) yielded identical results indicating that the origin of the lack of reactivity of cytochrome a3 is of a kinetic nature. The effect of increasing the ionic strength on the reaction was 2-fold: a marked decrease in reaction rate and the appearance of biphasic kinetics with the amplitude of the very fast absorbance changes at 605 nm decreasing from 80% to 40% of the total anticipated from static absorbance measurements. Each of the two phases accounted for a maximum of 1 electron at the highest ionic strength employed. These results are simulated in terms of a sample kinetic reaction scheme involving a two-step electron transfer at one binding site.
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PMID:Kinetic characterization of the interaction between cytochrome oxidase and cytochrome c. 628 Dec 61

Upon photolysis at 355 nm, dioxygen is released from a (mu-peroxo)(mu-hydroxo)bis[bis(bipyridyl)cobalt-(III)] complex in aqueous solutions and at physiological pH with a quantum yield of 0.04. The [Co(bpy)2(H2O)2]2+ (bpy = bipyridyl) photoproduct was generated on a nanosecond or faster time scale as determined by time-resolved optical absorption spectroscopy. A linear correspondence between the spectral changes and the oxygen production indicates that O2 is released on the same time scale. Oxyhemoglobin was formed from deoxyhemoglobin upon photodissociation of the (mu-peroxo) (mu-hydroxo)bis[bis(bipyridyl)cobalt(III)] complex, verifying that dioxygen is a primary photoproduct. This complex and other related compounds provide a method to study fast biological reactions involving O2, such as the reduction of dioxygen to water by cytochrome oxidase.
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PMID:Photodissociation of a (mu-peroxo)(mu-hydroxo)bis[bis(bipyridyl)-cobalt(III)] complex: a tool to study fast biological reactions involving O2. 766 52

The objective was to obtain detailed topographic determinations of cytochrome oxidase activity in the gerbil central auditory system at the light microscopic level. Quantitative techniques were developed using (1) tissue standards calibrated to express histochemical measures as actual enzyme activity units, (2) densitometry and image analysis of histochemical reaction product formation, (3) spectrophotometry of cytochrome oxidase activity, and (4) a cobalt-intensified staining procedure compatible with autoradiography and other techniques requiring fresh-frozen brains without perfusion-fixation. Linear relationships between incubation time, section thickness, and activity of dissected brain regions, with their reaction product measured densitometrically were determined. Auditory structures with the high activities showed about 8 times the labeling intensity of the white matter or control sections inhibited with cyanide, glutaraldehyde, or heat. This indicated the high sensitivity of the method without loss of specificity. Specific activity for each of the 18 auditory structures measured were all above the units measured for whole brain homogenates, supporting the notion that basal levels of oxidative metabolism are greater for the auditory system. There was a progressive decrement in activity from brain stem to forebrain auditory structures. The more peripheral nuclei also showed a higher proportion of somatic as compared to neuropil reactivity. In contrast, auditory midbrain and thalamocortical regions were characterized primarily by neuropil reactivity. Comparison of intrinsic patterns of activity with morphological schemes to subdivide nuclei, showed a good correspondence with classical subdivisions derived from Golgi studies. The reported activities may provide a base of normative data in the gerbil for subsequent studies of central auditory functions. The method presented fulfilled established quantitative criteria and provided a more sensitive approach for regional mapping studies of brain cytochrome oxidase activity.
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PMID:Quantitative mapping of cytochrome oxidase activity in the central auditory system of the gerbil: a study with calibrated activity standards and metal-intensified histochemistry. 782

Detailed qualitative and quantitative determinations of cytochrome oxidase activity in the central auditory system of BALB/cJ mice were obtained at the light microscopic level. Cytochrome oxidase activity was determined using quantitative densitometry calibrated with standards of spectrophotometrically assayed enzymatic activity. This was done together with a cobalt-intensified histochemical procedure using fresh-frozen brains without perfusion-fixation. The resulting method showed improved sensitivity and allowed quantification of histochemical labeling as actual enzyme activity units. Adjacent sections were processed for either Nissl, fiber or Golgi stains to correlate the histochemical labeling with tissue morphology. The more peripheral auditory nuclei showed primarily somatic labeling with specific cell types showing predominant reactivity. However, higher auditory structures, including the inferior colliculus, medial geniculate and auditory cortex, showed predominantly neuropil reactivity. Comparison of mean cytochrome oxidase activities for the 27 auditory regions quantified revealed a trend for decreasing activity from the brainstem to the forebrain in central lemniscal structures. The extra-lemniscal auditory regions at each level showed lower activity than the corresponding lemniscal regions. The regions with the higher activity values showed around 10 times the labeling density of the white matter, indicating the high sensitivity of the method. The darkly labeling auditory structures were clearly delineated from surrounding neural regions, supporting the concept that basal levels of oxidative metabolic capacity are larger for the auditory system. It was concluded that the quantitative approach to cytochrome oxidase histochemistry may be applied successfully to the mouse brain. The normative data presented may be used as a starting point for other investigations of the effects of experimental manipulations on the metabolic activity of the auditory system.
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PMID:Cytochrome oxidase activity in the auditory system of the mouse: a qualitative and quantitative histochemical study. 789 65

The hypoxia-induced increase of spectrophotometrically measured light absorption at 560 nm, considered as reduced cytochrome b, in HepG2 cells is diminished after exposure to cobalt chloride (50 or 100 microM) for 18-36 h. The redox state of cytochrome c and cytochrome aa3, however, remains stable, indicating a particular affinity of cytochrome b for cobalt. Erythropoietin production of HepG2 cells increases after application of cobalt chloride, whereas H2O2 production, as measured by the dihydrorhodamine technique, decreases. It is concluded that cobalt stimulates a signal cascade with cytochrome b as receptor and H2O2 as second messenger for regulating erythropoietin production.
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PMID:Effects of cobalt on haem proteins of erythropoietin-producing HepG2 cells in multicellular spheroid culture. 803 45

Cobalt and desferrioxamine, like hypoxia, stimulate the production of erythropoietin in HepG2 cells. It is believed that cobalt as well as desferrioxamine interact with the central iron atom of heme proteins by changing their redox state similar to hypoxia. A subsequent decrease of the intracellular H2O2 levels under hypoxia was presumed to be the key event for stimulating erythropoietin production. We therefore investigated whether cobalt and desferrioxamine control the intracellular H2O2 levels that regulate gene expression by interacting with hemeproteins. Deconvolution of light absorption spectra revealed respiratory heme proteins such as cytochrome c, b558 and cytochrome aa3, as well as cytochrome b558, which is a nonrespiratory heme protein found in HepG2 cells. Whereas respiratory heme proteins are located in mitochondria, cytochrome b558 similar to the one described for the neutrophil NADPH oxidase can be visualized in the cell membrane of HepG2 cells by immunohistochemistry. Incubation with cobalt (100 microM/24 hr) interacts predominantly with cytochrome b558 and cytochrome b558. The interaction of cobalt with the respiratory chain results in an increased oxygen consumption of HepG2 cells as revealed by PO2 microelectrode measurements. Desferrioxamine (130 microM/24 hr), however has no influence on the cytochromes. In response to an external application of NADH (1 mM), the membrane bound cytochrome b558 produces two times more O2- than to the external NADPH (1 mM) application. Neither desferrioxamine not cobalt has any influence on the NADH stimulated O2- generation. Incubation with cobalt or with desferrioxamine, however, leads to a decrease of the intracellular H2O2 level as revealed by the dihydrorhodamine 123 technique, perhaps causing the well-known enhanced erythropoietin production. The cobalt-induced H2O2 decrease seems to be caused by an increased activity of the glutathion peroxidase that is also induced under hypoxia. Desferrioxamine, however, leads to an apparent H2O2 decrease only because it seems to inhibit the iron catalyzed reaction of H2O2 with dihydrorhodamine 123, hinting at the occurrence of the Fenton reaction in HepG2 cells. Therefore, it must be determined whether or not degradation products of H2O2 by the Fenton reaction suppress erythropoietin production under normoxia.
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PMID:Cobalt and desferrioxamine reveal crucial members of the oxygen sensing pathway in HepG2 cells. 902 27

This study was conducted to investigate the physiological consequences of long-term moderate cobalt deficiency in beef cattle, which have not hitherto been studied in detail. Cobalt deficiency was induced in cattle by feeding two groups of animals either a basal corn silage-based diet that was moderately low in cobalt (83 micrograms Co/kg), or the same diet supplemented with cobalt to a total of 200 micrograms per kg, for 43 weeks. Cobalt deficiency was induced, as judged by inappetance, diminished growth gain and a markedly reduced vitamin B12 status in serum and liver. The long-term cobalt deprivation which was primarily a combination of reduced feed intake and a tissue vitamin B12 deficiency did not show evidence of a significant dysfunction of energy metabolism. The activities of glucose-6-phosphate dehydrogenase and cytochrome oxidase in liver remained unaffected by cobalt deficiency, nor was there a significant change in serum glucose level of cattle on the cobalt-deprived diet. However, analysis of thyroid hormone status indicated a slight reduction of type I thyroxine monodeiodinase activity in liver accompanied by a significant reduction of the triiodothyronine level in serum. The diminished liver vitamin B12 level resulted in significantly reduced folate level in this tissue, reduced concentrations of heme-depending blood parameters. Moreover cobalt deficiency or rather vitamin B12 deficiency was accompanied by a dramatic accumulation of the trace elements iron and nickel in liver. These results indicate that long-term moderate cobalt deficiency may induce a number of physiological changes in cattle, but a follow-up study, which excluded different feed levels by including a pair-fed control group, will be necessary to actually obtain the single effect of cobalt deficiency in cattle.
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PMID:Cobalt deficiency effects on trace elements, hormones and enzymes involved in energy metabolism of cattle. 1021 49

We describe a new method for studying rapid biological reactions involving dioxygen. This approach is based on the photolysis of a synthetic caged dioxygen carrier, which produces dioxygen on a fast time scale. The method was used to investigate the reduction of dioxygen to water by cytochrome c oxidase at room temperature following photolysis of a (mu-peroxo)(mu-hydroxo)bis[bis(bipyridyl)c obalt(III)] complex. The fact that dioxygen is generated in situ on a nanosecond or faster time scale avoids potential complications related to the fate of photodissociated CO in a conventional CO flow-flash experiment. The cobalt complex is stable at room temperature under anaerobic conditions and releases dioxygen upon irradiation at 355 nm with a quantum yield of 0.04. The complex does not react with reduced cytochrome oxidase or its reducing agents within the mixing time of the experiment, and its photoproducts do not interfere with the kinetics of the dioxygen reduction. The oxidation of the reduced cytochrome oxidase was monitored between 500 and 750 nm using a gated optical spectrometric multichannel analyzer following photodissociation of the cobalt complex. The data were analyzed using singular value decomposition and global exponential fitting, and two apparent lifetimes (380 +/- 50 micros and 1.7 +/- 0.2 ms) were resolved and compared to results from a conventional CO flow-flash experiment. The results show that approximately 90 microM dioxygen can be generated upon a single laser pulse and that this approach can be used to study other fast biological reactions involving O(2).
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PMID:A new approach for studying fast biological reactions involving dioxygen: the reaction of fully reduced cytochrome c oxidase with O2. 1108 13

A bacterial two-hybrid assay revealed interaction between a protein now designated bacterial Atx1 and amino-terminal domains of copper-transporting ATPases CtaA (cellular import) and PacS (thylakoid import) but not the related zinc (ZiaA) or cobalt (CoaT) transporters from the same organism (Synechocystis PCC 6803). The specificity of metallochaperone interactions coincides with metal specificity. After reconstitution in a N(2) atmosphere, bacterial Atx1 bound 1 mol of copper mol(-1), and apoPacS(N) acquired copper from copper-Atx1. Copper was displaced from Atx1 by p-(hydroxymercuri)phenylsulfonate, indicative of thiol ligands, and two cysteine residues were obligatory for two-hybrid interaction with PacS(N). This organism contains compartments (thylakoids) where the copper proteins plastocyanin and cytochrome oxidase reside. In copper super-supplemented mutants, photooxidation of cytochrome c(6) was greater in Deltaatx1DeltactaA than in DeltactaA, showing that Atx1 contributes to efficient switching from iron in cytochrome c(6) to copper in plastocyanin for photosynthetic electron transport. Cytochrome oxidase activity was also less in membranes purified from low [copper]-grown Deltaatx1 or DeltapacS, compared with wild-type, but the double mutant Deltaatx1DeltapacS was non-additive, consistent with Atx1 acting via PacS. Conversely, activity in Deltaatx1DeltactaA was less than in either respective single mutant, revealing that Atx1 can function without the major copper importer and consistent with a role in recycling endogenous copper.
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PMID:A copper metallochaperone for photosynthesis and respiration reveals metal-specific targets, interaction with an importer, and alternative sites for copper acquisition. 1173 76

We developed the synthesis of the caged oxygen donor (micro-peroxo)(micro-hydroxo)bis[bis(bipyridyl)cobalt(III)] complex (HPBC) as nitrate salt, which has, compared with the perchlorate-form described previously [MacArthur, R., Sucheta, A., Chong, F.F. & Einarsdottir, O. (1995) Proc. Natl Acad. Sci. USA, 92, 8105-8109], greatly enhanced solubility. Now, the quantum efficiency of the photolytical release of dioxygen was determined to be 0.4 per photon at a laser wavelength of 308 nm, which was used to observe biological reactions. The X-ray structure of HPBC has been solved, and the molecular interactions of photochemically generated oxygen with cytochrome oxidase were investigated with optical and FT-IR spectroscopy: it acts as acceptor of electrons transferred from prereduced cytochrome bo(3), the heme-copper oxidase from Escherichia coli. FT-IR spectra revealed typical absorbance difference changes in the carbonyl region of cytochrome bo(3), supported by bandshifts due to solvent isotope exchange and by assignment using site-directed mutants. IR difference spectra of the photooxidation reaction using the caged oxygen compound, and of the photoreduction reaction using the caged electron donor FMN, have inverted shapes. The spectroscopic signals of carboxyl groups are thus equivalent in both reactions: the use of chemically produced oxygen allows the observation of the ongoing molecular changes of cytochrome bo(3) oxidase under quasi-physiological conditions.
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PMID:Caged O(2). Reaction of cytochrome bo(3) oxidase with photochemically released dioxygen from a cobalt peroxo complex. 1202 3


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