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Query: UNIPROT:O14944 (EPR)
 13,097 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Superoxide radicals in high concentrations were generated from alkaline H2O2 without using catalysts or irradiation. The dependence of the intensity and parameters of the superoxide radical EPR spectrum on pH, temperature, viscosity and H2O2 concentration were studied. The observed changes are explained on the base of matrix effects. The addition of superoxide dismutase to alkaline H2O2 led initially to a drop in the EPR spectrum intensity, followed by an increase in the concentration of superoxide radicals.
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PMID:Generation of superoxide radicals in alkaline solutions of hydrogen peroxide and the effect of superoxide dismutase on this system. 3 70

1) It was demonstrated by colorimetric as well as EPR measurements that the native (aerobic, resting state) Rhus vernicifera laccase contains both Cu2+ and Cu+ (total Cu content was 4.0 gram atoms/mole). The ratio of Cu2+ to total Cu in laccase varied (42-90%) in samples of latex collected from various districts. The absorption maximum at 615 nm was proportional to the content of total Cu in the enzyme sample. Laccase activity was found to almost parallel the content of the Cu2+ form. The oxidized minus reduced difference absorbance of the enzyme at 330 nm shoulder was proportional to the amount of Cu2+. 2) Steady state level of oxidation of laccase copper during the laccase copper catalytic action, the rates of reduction by substrates and the oxidation by O2 were determined by following absorbance changes at 615 and 330 nm by the stopped flow method. 3) All the results from titrimetric and kinetic experiments were consistent with the laccase model previously proposed by Makino and Ogura in which a laccase molecule contains 1 Cu(615) and 3 Cu(330). Our expanded model states that a laccase sample originally contains active as well as inactive enzymes. In the active enzyme, Cu ions are reactive to O2 but in the inactive enzyme, Cu can be oxidized only by oxidizing agents such as H2O2 or ferricyanide, or by a slow intermolecular electron transfer from Cu(615) to the active enzyme. In both species of enzyme rapid reduction of Cu2+ ions by substrate takes place. In comparative studies of the reactivities of Cu ions in various copper proteins, we would like to suggest that oxidatic activity of a copper protein is due to the Cu+ form of the enzyme ions with O2.
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PMID:Oxidation and reduction of copper ions in catalytic reactions of Rhus laccase. 13 27

Compound I of horseradish peroxidase (donor: hydrogen-peroxide oxidoreductase EC 1.11.1.7) was studied by EPR at low temperatures. An asymmetric signal was found, about 15 Gauss wide and with a g-value of 1.995, which could be detected only at temperatures below 20 K and which had an intensity corresponding to about 1% of the heme content. In a titration with H2O2, the signal intensity was proportional to the concentration of Compound I, reaching a maximum when equivalent amounts of H2O2 were added. This indicates that the signal is not due to an impurity, and it is suggested that a free radical is formed, relaxed by a near-by fast-relaxing iron.
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PMID:EPR studies on compound I of horseradish peroxidase. 16 31

1. A rapid isolation procedure with a high yield for pure myeloperoxidase (donor:H2O2 oxidoreductase, EC 1.11.1.7) from normal human leucocytes is described. The enzyme was solubilized from leucocytes with the detergent, cetyltrimethylammonium bromide, and purified to apparent homogeneity. The yield of the enzyme was 17% with an absorbance ratio A430nm/A280nm = 0.85. 2. The purified enzyme showed three isoenzyme bands after polyacrylamide gel electrophoresis; ultracentrifuge studies indicated one homogeneous band with a molecular weight of 144 000. After reduction of myeloperoxidase, sodium dodecyl sulfate gel electrophoresis resolved an intense band (63 000 daltons) and a weak band (81 000 daltons). 3. The carbohydrate content of the enzyme was at least 2.5%. Mannose, glucose and N-acetylglucosamine were present. The amino acid composition is reported. 4. The EPR spectrum exhibited a high-spin heme signal with rhombic symmetry (gx = 6.92, gy = 5.07 and gz = 1.95). Upon acidification this signal was converted into a signal with more axial symmetry (g perpendicular = 5.89). At high pH (9.5) the EPR spectrum of the enzyme only shows low-spin ferric heme resonances. The circular dichroism spectra of ferric and ferrous myeloperoxidase in the visible and ultraviolet region show maxima and minima in ellipticity.
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PMID:Isolation procedure and some properties of myeloperoxidase from human leucocytes. 20 40

The reactivity of several thiols, including glutathione, dihydrolipoic acid, cysteine, N-acetyl cysteine, and ergothioneine, as well as several disulfides, toward different redox states of myoglobin, mainly met-myoglobin (HX-FeIII) and ferrylmyoglobin (HX-FeIV=O), was evaluated by optical spectral analysis, product formation, and thiyl free radical generation. Only dihydrolipoic acid reduced met-myoglobin to oxy-myoglobin, whereas all the other thiols tested did not interact with met-myoglobin. Although the redox transitions involved in the former reduction were expected to yield the dihydrolipoate thiyl radical, the reaction was EPR silent. Conversely, all thiols interacted to different extent with the high oxidation state of myoglobin, i.e. ferrylmyoglobin, via two processes. First, direct electron transfer to heme iron in ferrylmyoglobin (HX-FeIV=O) with formation of met-myoglobin (HX-FeIII) or oxymyoglobin (HX-FeIIO2); the former transition was effected by all thiols except dihydrolipoate, which facilitated the latter, i.e. the formation of the two-electron reduction product of ferrylmyoglobin. Second, nucleophilic addition onto a pyrrole in ferrylmyoglobin with subsequent formation of sulfmyoglobin. The contribution of either direct electron transfer to the heme iron or nucleophilic addition depended on the physicochemical properties of the thiol involved and on the availability of H2O2 to reoxidize met-myoglobin to ferrylmyoglobin. The thiyl radicals of glutathione, cysteine, and N-acetylcysteine were formed during the interaction of the corresponding thiols with ferrylmyoglobin and detected by EPR in conjunction with the spin trap 5,5'-dimethyl-1-pyroline-N-oxide. The intensity of the EPR signal was insensitive to superoxide dismutase and it was decreased, but not suppressed, by catalase. The disulfides of glutathione and cysteine did not react with ferrylmyoglobin, but the disulfide bridge in lipoic acid interacted efficiently with the ferryl species by either reducing directly the heme iron to form met-myoglobin or adding onto a pyrrole ring to form sulfmyoglobin; either process depended on the presence or absence of catalase (to eliminate the excess of H2O2) in the reaction mixture, respectively. The biological significance of the above results is discussed in terms of the occurrence and distribution of high oxidation states of myoglobin, its specific participation in cellular injury, and its potential interaction with biologically important thiols leading to either recovery of myoglobin or generation of nonfunctional forms of the hemoprotein as sulfmyoglobin.
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PMID:The reactivity of thiols and disulfides with different redox states of myoglobin. Redox and addition reactions and formation of thiyl radical intermediates. 130 91

Tiron (1,2-dihydroxybenzene-3,5-disulfonate), a nontoxic chelator of a variety of metals, is used to alleviate acute metal overload in animals. It is also oxidized to the EPR-detectable semiquinone radical by various biologically relevant oxidants, such as .OH, O2-., alkyl, and alkoxyl radicals. Since Tiron reacts with potentially toxic intracellular species and is also a metal chelator, we evaluated its protective effects in V79 cells subjected to various types of oxidative damage and attempted to distinguish the protection due to direct detoxification of intracellular radicals from that resulting from chelation of redox-active transition metals. We found that Tiron protects Chinese hamster V79 cells against both O2.(-)-induced (and H2O2 via dismutation of O2.-) and H2O2-induced cytotoxicity as measured by clonogenic assays. In experiments where Tiron was incubated with V79 cells and rinsed prior to exposure to HX/XO or H2O2, cytoprotection was observed, indicating that it protects against intracellular oxidative damage. On the other hand, Tiron did not protect V79 cells against the damage caused by ionizing radiation under aerobic conditions, which is predominantly mediated by H., .OH, and hydrated electrons in a metal-independent fashion. We demonstrate also that in in vitro studies, Tiron protects supercoiled DNA from metal-mediated superoxide-dependent strand breaks. We conclude that Tiron is a potentially useful protecting agent against the lethal effects of oxidative stress and suggest that it offers protection by chelating redox-active transition metal ions, in contrast to earlier reports where the protection by this compound in cellular systems subjected to oxidative damage has been interpreted as due to radical scavenging alone.
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PMID:The catecholic metal sequestering agent 1,2-dihydroxybenzene-3,5-disulfonate confers protection against oxidative cell damage. 131 13

Copper-induced oxidative damage is generally attributed to the formation of the highly reactive hydroxyl radical by a mechanism analogous to the Haber-Weiss cycle for Fe(II) and H2O2. In the present work, the reaction between the Cu(I) ion and H2O2 is studied using the EPR spin-trapping technique. The hydroxyl radical adduct was observed when Cu(I), dissolved in acetonitrile under N2, was added to pH 7.4 phosphate buffer containing 100 mM 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Formation of the hydroxyl radical was dependent on the presence of O2 and subsequent formation of H2O2. The kscav/kDMPO ratios obtained were below those expected for a mechanism involving free hydroxyl radical and reflect the interference of nucleophilic addition of H2O to DMPO to form the DMPO/.OH adduct in the presence of nonchelated copper ion. Addition of ethanol or dimethyl sulfoxide to the reaction suggests that a high-valent metal intermediate, possibly Cu(III), was also formed. Spin trapping of hydroxyl radical was almost completely inhibited upon addition of Cu(I) to a solution of either nitrilotriacetate or histidine, even though the copper was fully oxidized to Cu(II) and H2O2 was formed. Bathocuproinedisulfonate, thiourea, and reduced glutathione all stabilized the Cu(I) ion toward oxidation by O2. Upon addition of H2O2, the Cu(I) in all three complexes was oxidized to varying degrees; however, only the thiourea complex was fully oxidized within 2 min of reaction and produced detectable hydroxyl radicals. No radicals were detected from the bathocuproinedisulfonate or glutathione complexes. Overall, these results suggest that the deleterious effects of copper ions in vivo are diminished by biochemical chelators, especially glutathione, which probably has a major role in moderating the toxicological effects of copper.
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PMID:Direct evidence for inhibition of free radical formation from Cu(I) and hydrogen peroxide by glutathione and other potential ligands using the EPR spin-trapping technique. 131 4

A sperm whale myoglobin gene containing multiple unique restriction sites has been constructed in pUC 18 by sequential assembly of chemically synthesized oligonucleotide fragments. Expression of the gene in Escherichia coli DH5 alpha cells yields protein that is identical to native sperm whale myoglobin except that it retains the terminal methionine. Site-specific mutagenesis has been used to prepare all the possible tyrosine----phenylalanine mutants of the recombinant myoglobin, including the three single mutants at Tyr-103, -146, and -151, the three double mutants, and the triple mutant. All of the mutant proteins are stable except the Tyr-103 mutant. Introduction of a second mutation (Lys-102----Gln) stabilizes the Tyr-103 mutant. Absorption spectroscopy suggests that the active sites of the mutant proteins are intact. EPR and absorption spectroscopy show that all the proteins, including the triple mutant devoid of tyrosine residues, react with H2O2 to give a ferryl species and a protein radical. The presence of a protein radical in all the mutants suggests that the radical center is readily transferred from one amino acid to another. Cross-linking studies show, however, that protein dimers are only formed when Tyr-151 is present. Tyr-103, shown earlier to be the residue that primarily cross-links to Tyr-151 (Tew, D., and Ortiz de Montellano, P. R. (1988) J. Biol. Chem. 263, 17880-17886), is not essential for cross-linking. Electron transfer from Tyr-151 to the heme, which are 12 A apart, occurs in the absence of the intervening tyrosines at positions 103 and 146. The present studies show that the peroxide-generated myoglobin radical readily exchanges between remote loci, including non-tyrosine residues, but protein cross-linking only occurs when radical density is located on Tyr-151.
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PMID:Intramolecular translocation of the protein radical formed in the reaction of recombinant sperm whale myoglobin with H2O2. 131 42

The soluble methane monooxygenase (MMO) system, consisting of reductase, component B, and hydroxylase (MMOH), catalyzes NADH and O2-dependent monooxygenation of many hydrocarbons. MMOH contains 2 mu-(H or R)oxo-bridged dinuclear iron clusters thought to be the sites of catalysis. Although rapid NADH-coupled turnover requires all three protein components, three less complex systems are also functional: System I, NADH, O2, reductase, and MMOH; System II, H2O2 and oxidized MMOH; System III, MMOH reduced nonenzymatically by 2e- and then exposed to O2 (single turnover). All three systems give the same products, suggesting a common reactive oxygen species. However, the distribution of products observed for most substrates that are hydroxylated in more than one position is different for each system. For several of these substrates, addition of component B to Systems I, II, or III causes the product distributions to shift dramatically. These shifts result in identical product distributions for Systems I and III in which MMOH passes through the 2e- reduced state ([Fe(II).Fe(II)]) during catalysis. In contrast, System II (in which MMOH probably does not become reduced) generally gives a unique product distribution. It is proposed that changes in MMOH structure occurring upon diiron cluster reduction and/or component complex formation cause substrates to be presented differently to the activated oxygen species. Kinetic studies show that component B strongly activates System I and, in most cases, strongly deactivates System II. The effect of component B on product distribution of System I (and III) occurs at less than 5% of the MMOH concentration, while nearly stoichiometric concentrations are required to maximize the rate of System I. This shows that component B has at least two roles in catalysis. EPR monitored titration of reduced MMOH ([Fe(II).Fe(II)]) with component B suggests that the effect of substoichiometric component B on product distribution is due to hysteresis in the MMOH conformational changes.
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PMID:Methane monooxygenase component B and reductase alter the regioselectivity of the hydroxylase component-catalyzed reactions. A novel role for protein-protein interactions in an oxygenase mechanism. 132 41

Electron spin resonance spectroscopy and the spin trapping technique were used to study the formation of the superoxide radical in pyridine. 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) was employed as a trapping agent. Superoxide radical was generated using chemical (potassium superoxide) and photochemical methods with anthralin, benzanthrone, rose bengal, 1,8-dihydroxyanthraquinone and zinc tetraphenylporphyrine as photoactive pigments. Hyperfine coupling (hf) constants for DMPO/O2.- were determined to be aN = 12.36 G, a beta H = 9.85, G, a gamma H = 1.34 G. The aN and a beta H hf constants are in good agreement with values calculated from a previously determined relationship between hf constants and solvent acceptor number (Reszka et al., (1992) Free Radical Res. Commun., in press). When concentrated hydrogen peroxide was added to DMPO in pyridine a similar EPR spectrum was observed. It is suggested that in this case the DMPO/.O2H adduct is formed by nucleophilic addition of H2O2 to DMPO to give a hydroxylamine, followed by oxidation to the respective nitroxide. The EPR spectrum observed when tetrapropylammonium hydroxide and H2O2 were added to DMPO in pyridine had hf couplings aN = 13.53 G, a beta H = 11.38 G, a gamma H = 0.79 G and it was assigned to a DMPO/.OH adduct. This assignment was based on similarity of this spectrum to the one produced by UV photolysis of hydrogen peroxide and DMPO in aqueous solution and subsequent transfer to pyridine.
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PMID:EPR spectra of DMPO spin adducts of superoxide and hydroxyl radicals in pyridine. 133 36


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