Involvement of the superoxide anion in sulphoxidation.
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ABSTRACT:
SUBMITTER: Prema K
PROVIDER: S-EPMC1166089 | biostudies-other | 1974 Jan
REPOSITORIES: biostudies-other
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Project description:The sigmoidal time course of haemoglobin oxidation by nitrite, involving an initial slow reaction accompanied by a subsequent rapid reaction, was extensively explored. The initial slow reaction was much prolonged by the addition of superoxide dismutase to the reaction mixture. On the other hand, in the presence of superoxide anion generated by xanthine oxidase systems, the slow phase disappeared and the reaction changed to first-order kinetics. The oxidation of intermediate haemoglobins [defined as haemoglobin tetramer in which different chains (alpha- or beta-) are in the ferric state and in the ferrous state] such as (alpha 2+ beta 3+)2 and (alpha 3+ beta 2+)2 also proceeded in a sigmoidal manner. Similar effects of superoxide anion on these reactions were observed. Since the intermediate haemoglobins such as (alpha 2+ beta 3+)2 and (alpha 3+ beta 2+)2 were found to be produced by the oxidation of haemoglobin by nitrite, the changes in oxyhaemoglobin, intermediate haemoglobins and methaemoglobin during the reaction were followed by isoelectric-focusing electrophoresis. The amounts of (alpha 2+ beta 3+)2 were larger than those of (alpha 3+ beta 2+)2 at the initial stages of the reaction, suggesting that there is a functional difference between alpha- and beta-chains in the oxyhaemoglobin tetramer. On the basis of these results, a reaction model of the haemoglobin oxidation by nitrite was tentatively proposed. The changes in oxyhaemoglobin, intermediate haemoglobins and methaemoglobin were well fitted to the simulation curves generated from the reaction model. Details of the derivation of the equations used for kinetic analysis have been deposited as Supplement SUP 50112 (5 pages) with the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K. from whom copies may be obtained on the terms indicated in Biochem. J. (1978) 169, 5.
| S-EPMC1162587 | biostudies-other
Project description:Lithium peroxide is the crucial storage material in lithium-air batteries. Understanding the redox properties of this salt is paramount toward improving the performance of this class of batteries. Lithium peroxide, upon exposure to p-benzoquinone (p-C6H4O2) vapor, develops a deep blue color. This blue powder can be formally described as [Li2O2][Formula: see text] [LiO2][Formula: see text] {Li[p-C6H4O2]}0.7, though spectroscopic characterization indicates a more nuanced structural speciation. Infrared, Raman, electron paramagnetic resonance, diffuse-reflectance ultraviolet-visible and X-ray absorption spectroscopy reveal that the lithium salt of the benzoquinone radical anion forms on the surface of the lithium peroxide, indicating the occurrence of electron and lithium ion transfer in the solid state. As a result, obligate lithium superoxide is formed and encapsulated in a shell of Li[p-C6H4O2] with a core of Li2O2 Lithium superoxide has been proposed as a critical intermediate in the charge/discharge cycle of Li-air batteries, but has yet to be isolated, owing to instability. The results reported herein provide a snapshot of lithium peroxide/superoxide chemistry in the solid state with redox mediation.
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Project description:Global Gene Expression Analysis Reveals Differences in Cellular Responses to Hydroxyl- and Superoxide-induced Oxidative Stress in Caco-2 Cells. Reactive oxygen species-induced oxidative stress in the colon is involved in inflammatory bowel diseases and is suggested to be associated with colorectal cancer risk. However, our insight in molecular responses to different oxygen radicals is still fragmentary. Therefore, we studied global gene expression by an extensive time serie (0.08, 0.25, 0.5, 1, 2, 4, 8, 16, or 24 hours ) analyses in human colon cancer (Caco-2) cells after exposure to H2O2 or menadione, leading to the formation of HO. or O2.- radicals respectively. Next to gene expression, induction of pathways and correlations with related phenotypic markers (oxidative DNA damage, cell cycle arrest) was investigated. Gene expression analysis resulted in 1404 differentially expressed genes upon H2O2 challenge and 979 genes after menadione treatment. Time-dependent co-regulated genes immediately showed a pulse-like response to HO. formation while the O2.--induced expression is not restored over 24 hours. Pathway analyses demonstrated that the difference in the modulation of gene expression is also reflected in regulation of pathways by HO. and O2.-: H2O2 immediately influences pathways involved in the immune function, while menadione constantly regulated cell cycle-related pathways. Altogether, this study offers a novel and detailed insight in differential time-dependent oxidative stress response, but most importantly, shows that effects of HO. and O2.- can also be discriminated regarding their modulation of particular carcinogenesis-related mechanisms. Keywords: Comparison of genome-wide gene expression between different time points for H2O2 and menadione.
2010-01-12 | GSE15327 | GEO
Project description:Superoxide anion is produced during normal cellular respiration and plays key roles in cellular physiology with its dysregulation being associated with a variety of diseases. Superoxide anion is a short-lived molecule and, therefore, its homeostatic regulation and role in biology and disease requires dynamic quantification with fine temporal resolution. Here we validated coelenterazine as a reporter of intracellular superoxide anion concentration and used it as a dynamic measure both in vitro and in vivo. Chemiluminescence was dependent upon superoxide anion levels, including those produced during cellular respiration, and concentrations varied both kinetically and temporally in response to physiologically relevant fluctuations in glucose levels. In vivo imaging with coelenterazine revealed that beta cells of the pancreas have increased levels of superoxide anion, which acted as a measure of beta-cell function and mass and could predict the susceptibility of mice to diabetes mellitus. Glucose response and regulation are key elements of cellular physiology and organismal biology, and superoxide anion appears to play a fundamental and dynamic role in both of these processes.
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Project description:Superoxide (O2•-) is a toxic radical, generated via the adventitious reduction of dioxygen (O2), which has been implicated in a number of human disease states. Nonheme iron enzymes, superoxide reductase (SOR) and superoxide dismutase (SOD), detoxify O2•- via reduction to afford H2O2 and disproportionation to afford O2 and H2O2, respectively. The former contains a thiolate in the coordination sphere, which has been proposed to prevent O2•- oxidation to O2. The work described herein shows that, in contrast to this, oxidized thiolate-ligated [FeIII(SMe2N4(tren)(THF)]2+ (1ox-THF) is capable of oxidizing O2•- to O2. Coordinating anions, Cl- and OAc-, are shown to inhibit dioxygen evolution, implicating an inner-sphere mechanism. Previously we showed that the reduced thiolate-ligated [FeII(SMe2N4(tren))]+ (1) is capable of reducing O2•- via a proton-dependent inner-sphere mechanism involving a transient Fe(III)-OOH intermediate. A transient ferric-superoxo intermediate, [FeIII(SMe2N4(tren))(O2)]+ (3), is detected by electronic absorption spectroscopy at -130 °C in the reaction between 1ox-THF and KO2 and shown to evolve O2 upon slight warming to -115 °C. The DFT calculated O-O (1.306 Å) and Fe-O (1.943 Å) bond lengths of 3 are typical of ferric-superoxo complexes, and the time-dependent DFT calculated electronic absorption spectrum of 3 reproduces the experimental spectrum. The electronic structure of 3 is shown to consist of two antiferromagnetically coupled (Jcalc = -180 cm-1) unpaired electrons, one in a superoxo π*(O-O) orbital and the other in an antibonding π*(Fe(dyz)-S(py)) orbital.
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Project description:Typically, simple flavoprotein oxidases couple the oxidation of their substrates with the formation of hydrogen peroxide without release of significant levels of the superoxide ion. However, two evolutionarily related single-domain sulfhydryl oxidases (Erv2p; a yeast endoplasmic reticulum resident protein and augmenter of liver regeneration, ALR, an enzyme predominantly found in the mitochondrial intermembrane) release up to ~30% of the oxygen they reduce as the superoxide ion. Both enzymes oxidize dithiol substrates via a redox-active disulfide adjacent to the flavin cofactor within the helix-rich Erv domain. Subsequent reduction of the flavin is followed by transfer of reducing equivalents to molecular oxygen. Superoxide release was initially detected using tris(3-hydroxypropyl)phosphine (THP) as an alternative reducing substrate to dithiothreitol (DTT). THP, and other phosphines, showed anomalously high turnover numbers with Erv2p and ALR in the oxygen electrode, but oxygen consumption was drastically suppressed upon the addition of superoxide dismutase. The superoxide ion initiates a radical chain reaction promoting the aerobic oxidation of phosphines with the formation of hydrogen peroxide. Use of a known flux of superoxide generated by the xanthine/xanthine oxidase system showed that one superoxide ion stimulates the reduction of 27 and 4.5 molecules of oxygen using THP and tris(2-carboxyethyl)phosphine (TCEP), respectively. This superoxide-dependent amplification of oxygen consumption by phosphines provides a new kinetic method for the detection of superoxide. Superoxide release was also observed by a standard chemiluminescence method using a luciferin analogue (MCLA) when 2 mM DTT was employed as a substrate of Erv2p and ALR. The percentage of superoxide released from Erv2p increased to ~65% when monomeric mutants of the normally homodimeric enzyme were used. In contrast, monomeric multidomain quiescin sulfhydryl oxidase enzymes that also contain an Erv FAD-binding fold release only 1-5% of their total reduced oxygen species as the superoxide ion. Aspects of the mechanism and possible physiological significance of superoxide release from these Erv-domain flavoproteins are discussed.
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