Endogenous Superoxide Dismutase Levels Regulate Iron-Dependent Hydroxyl Radical Formation in Escherichia coli Exposed to Hydrogen Peroxide
01 Feb 1998-Journal of Bacteriology (American Society for Microbiology)-Vol. 180, Iss: 3, pp 622-625
TL;DR: The hypothesis that a resulting increase in .OH formation generated by Fenton chemistry is responsible for the observed enhancement of DNA damage and the increased susceptibility to H2O2-mediated killing seen in these mutants lacking SOD is supported.
Abstract: Aerobic organisms contain antioxidant enzymes, such as superoxide dismutase (SOD) and catalase, to protect them from both direct and indirect effects of reactive oxygen species, such as O2.- and H2O2. Previous work by others has shown that Escherichia coli mutants lacking SOD not only are more susceptible to DNA damage and killing by H2O2 but also contain larger pools of intracellular free iron. The present study investigated if SOD-deficient E. coli cells are exposed to increased levels of hydroxyl radical (.OH) as a consequence of the reaction of H2O2 with this increased iron pool. When the parental E. coli strain AB1157 was exposed to H2O2 in the presence of an alpha-(4-pyridyl-1-oxide)-N-tert-butyl-nitrone (4-POBN)-ethanol spin-trapping system, the 4-POBN-.CH(CH3)OH spin adduct was detectable by electron paramagnetic resonance (EPR) spectroscopy, indicating .OH production. When the isogenic E. coli mutant JI132, lacking both Fe- and Mn-containing SODs, was exposed to H2O2 in a similar manner, the magnitude of .OH spin trapped was significantly greater than with the control strain. Preincubation of the bacteria with the iron chelator deferoxamine markedly inhibited the magnitude of .OH spin trapped. Exogenous SOD failed to inhibit .OH formation, indicating the need for intracellular SOD. Redox-active iron, defined as EPR-detectable ascorbyl radical, was greater in the SOD-deficient strain than in the control strain. These studies (i) extend recent data from others demonstrating increased levels of iron in E. coli SOD mutants and (ii) support the hypothesis that a resulting increase in .OH formation generated by Fenton chemistry is responsible for the observed enhancement of DNA damage and the increased susceptibility to H2O2-mediated killing seen in these mutants lacking SOD.
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01 Dec 2016
TL;DR: In this article, the authors present a survey of 5.7.8.7-8 and 5.5.7 -8.5-8.1-5.
Abstract: 7-8
TL;DR: In this paper, the row of heavy metals by its influence on Desulfovibrio desulfuricans Ya-11 catalase activity has been formed at first: ZnCl 2 > Pb(NO 3 ) 2 > CuCl 2> CdCl 2
Abstract: The highest catalase activity (42.67×10 – 2 µM×min – 1 ×mg – 1 of protein) in the cells of Desulfovibrio desulfuricans Ya-11 has been observed under the prolonged Pb(NO 3 ) 2 influence. In the presence of other heavy metals’ salts it has been changed in dependence on their concentrations and growth duration. Based on our research data the row of heavy metals’ salts by its influence on D. desulfuricans Ya-11 catalase activity has been formed at first: Pb(NO 3 ) 2 > CuCl 2 > CdCl 2 > ZnCl 2 . The highest superoxide dismutase activity (61.52×10 – 2 µM×min – 1 ×mg – 1 of protein) has been observed under the prolonged ZnCl 2 influence. In the presence of other heavy metals’ salts this enzyme’s activity increased with increasing the salts’ concentrations. Based on our According to our results, the row of heavy metals’ salts influence on D. desulfuricans Ya-11 superoxide dismutase activity has been formed at first: ZnCl 2 > Pb(NO 3 ) 2 > CuCl 2 > CdCl 2 .
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Book•
13 Jun 1985
TL;DR: 1. Oxygen is a toxic gas - an introduction to oxygen toxicity and reactive species, and the chemistry of free radicals and related 'reactive species'
Abstract: 1. Oxygen is a toxic gas - an introductionto oxygen toxicity and reactive species 2. The chemistry of free radicals and related 'reactive species' 3. Antioxidant defences Endogenous and Diet Derived 4. Cellular responses to oxidative stress: adaptation, damage, repair, senescence and death 5. Measurement of reactive species 6. Reactive species can pose special problems needing special solutions. Some examples. 7. Reactive species can be useful some more examples 8. Reactive species can be poisonous: their role in toxicology 9. Reactive species and disease: fact, fiction or filibuster? 10. Ageing, nutrition, disease, and therapy: A role for antioxidants?
21,528 citations
"Endogenous Superoxide Dismutase Lev..." refers background in this paper
...rapidly reacts with itself (dismutes) to form H2O2 (7)....
[...]
...Although the aerobic metabolism of bacteria optimally results in the near simultaneous four-electron reduction of O2 to H2O, a variable percentage of O2 reduction occurs initially via either one-electron reduction of O2 to superoxide (O2 ) or divalent reduction to H2O2 (7)....
[...]
TL;DR: It is proposed that the cell may also decrease such toxicity by diminishing available NAD(P)H and by utilizing oxygen itself to scavenge active free radicals into superoxide, which is then destroyed by superoxide dismutase.
Abstract: A major portion of the toxicity of hydrogen peroxide in Escherichia coli is attributed to DNA damage mediated by a Fenton reaction that generates active forms of hydroxyl radicals from hydrogen peroxide, DNA-bound iron, and a constant source of reducing equivalents. Kinetic peculiarities of DNA damage production by hydrogen peroxide in vivo can be reproduced by including DNA in an in vitro Fenton reaction system in which iron catalyzes the univalent reduction of hydrogen peroxide by the reduced form of nicotinamide adenine dinucleotide (NADH). To minimize the toxicity of oxygen radicals, the cell utilizes scavengers of these radicals and DNA repair enzymes. On the basis of observations with the model system, it is proposed that the cell may also decrease such toxicity by diminishing available NAD(P)H and by utilizing oxygen itself to scavenge active free radicals into superoxide, which is then destroyed by superoxide dismutase.
1,997 citations
"Endogenous Superoxide Dismutase Lev..." refers background in this paper
...Pretreatment of the JI132 (SOD-deficient) bacteria with DFO greatly reduced the magnitude of OH generation, confirming that it arose as a consequence of Fenton chemistry, as iron bound to DFO is no longer available for this redox chemistry (10)....
[...]
TL;DR: Aerotolerant anaerobes, which survive exposure to air and metabolize oxygen to a limited extent but do not contain cytochrome systems, were found to be devoid of catalase activity but did exhibit superoxide dismutase activity.
Abstract: The distribution of catalase and superoxide dismutase has been examined in various micro-organisms. Strict anaerobes exhibited no superoxide dismutase and, generally, no catalase activity. All aerobic organisms containing cytochrome systems were found to contain both superoxide dismutase and catalase. Aerotolerant anaerobes, which survive exposure to air and metabolize oxygen to a limited extent but do not contain cytochrome systems, were found to be devoid of catalase activity but did exhibit superoxide dismutase activity. This distribution is consistent with the proposal that the prime physiological function of superoxide dismutase is protection of oxygen-metabolizing organisms against the potentially detrimental effects of the superoxide free radical, a biologically produced intermediate resulting from the univalent reduction of molecular oxygen.
974 citations
"Endogenous Superoxide Dismutase Lev..." refers background in this paper
...Most bacteria, including Escherichia coli, contain superoxide dismutase (SOD) and catalase as means of eliminating O2 z2 and H2O2, respectively (16, 17)....
[...]
TL;DR: This presentation discusses the role of catalytic metals in free radical-mediated oxidations, ascorbate as both a pro-oxidant and an antioxidant, use of asCorbate to determine adventitious catalytic metal concentrations, and uses of ascorBate radical as a marker of oxidative stress.
Abstract: Trace levels of transition metals can participate in the metal-catalyzed Haber-Weiss reaction (superoxide-driven Fenton reaction) as well as catalyze the oxidation of ascorbate. Generally ascorbate is thought of as an excellent reducing agent; it is able to serve as a donor antioxidant in free radical-mediated oxidation processes. However, as a reducing agent it is also able to reduce redox-active metals such as copper and iron, thereby increasing the pro-oxidant chemistry of these metals. Thus ascorbate can serve as both a pro-oxidant and an antioxidant. In general, at low ascorbate concentrations, ascorbate is prone to be a pro-oxidant, and at high concentrations, it will tend to be an antioxidant. Hence there is a crossover effect. We propose that the "position" of this crossover effect is a function of the catalytic metal concentration. In this presentation, we discuss: (1) the role of catalytic metals in free radical-mediated oxidations; (2) ascorbate as both a pro-oxidant and an antioxidant; (3) catalytic metal catalysis of ascorbate oxidation; (4) use of ascorbate to determine adventitious catalytic metal concentrations; (5) use of ascorbate radical as a marker of oxidative stress; and (6) use of ascorbate and iron as free radical pro-oxidants in photodynamic therapy of cancer.
851 citations
TL;DR: In this article, the authors show that the level of loose iron in severely superoxide-stressed cells greatly exceeds that of unstressed cells, and that both growth defects and DNA damage caused by superoxide ensue from its ability to damage a subset of iron-sulfur clusters.
Abstract: Superoxide promotes hydroxyl-radical formation and consequent DNA
damage in cells of all types. The long-standing hypothesis that it
primarily does so by delivering electrons to adventitious iron on DNA
was refuted by recent studies in Escherichia coli.
Alternative proposals have suggested that superoxide may accelerate
oxidative DNA damage by leaching iron from storage proteins or enzymic
[4Fe-4S] clusters. The released iron might then deposit on the
surface of the DNA, where it could catalyze the formation of DNA
oxidants using other electron donors. The latter model is affirmed by
the experiments described here. Whole-cell electron paramagnetic
resonance demonstrated that the level of loose iron in
superoxide-stressed cells greatly exceeds that of unstressed cells.
Bacterial iron storage proteins were not the major source for free
iron, since superoxide also increased iron levels in mutants lacking
these iron storage proteins. However, overproduction of an enzyme
containing a labile [4Fe-4S] cluster dramatically increased the free
iron content of cells when they were growing in air. The rates of
spontaneous mutagenesis and DNA damage from exogenous
H2O2 increased commensurately. It is striking
that both growth defects and DNA damage caused by superoxide ensue from
its ability to damage a subset of iron–sulfur clusters.
803 citations