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:1.11.1.7 (peroxidase)
65,474 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanism of activation of the bladder carcinogen 2-amino-4-(5-nitro-2-furyl)thiazole (ANFT) was investigated by comparison with benzidine. In comparison with benzidine, ANFT has a higher electrochemical potential (approximately 700 mV) and is less effective as a reducing co-substrate for either prostaglandin H synthase (PHS) or horseradish peroxidase. Activation was monitored by measuring binding to protein (BSA) and DNA. ANFT binding to protein was reduced by indomethacin, a fatty acid cyclooxygenase inhibitor; phenol and aminopyrine, competitive reducing co-substrates; ascorbic acid, an antioxidant; and glutathione, thioether conjugate formation. These results are consistent with those previously reported for benzidine and demonstrate a peroxide co-substrate requirement, interaction of peroxidase with amine, formation of reactive intermediates and inactivation of reactive intermediates. 5,5-Dimethyl-1-pyrroline N-oxide (DMPO), a radical trap, also reduced ANFT binding to protein. Similar results were observed whether activation by PHS or horseradish peroxidase was investigated. Peroxidative activation of ANFT and benzidine to bind DNA was inhibited by these test agents in a manner similar to that observed with protein except that DMPO did not reduce binding. In addition, 2-methyl-2-nitrosopropane and methyl viologen, which are radical traps, and methionine and p-nitrobenzyl-pyridine, which are strong nucleophiles, did not reduce ANFT or benzidine binding to DNA. These agents also did not prevent binding of benzidinediimine, the two-electron product of benzidine oxidation, to polydeoxyguanosine. Glutathione inhibited diimine binding by forming a conjugate. Results demonstrate that activation of ANFT to bind protein and DNA is similar to benzidine. Peroxidative activation of benzidine occurs by both one- and two-electron oxidation. A similar mechanism would explain ANFT binding to protein (one electron) and DNA (two electron).
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PMID:Mechanism of peroxidative activation of the bladder carcinogen 2-amino-4-(5-nitro-2-furyl)-thiazole (ANFT): comparison with benzidine. 212 82

Aqueous solutions of cyanide react with hydrogen peroxide/horseradish peroxidase and form the cyanyl radical, which can be trapped by 2-methyl-2-nitrosopropane (t-nitrosobutane, tNB) at pH 9.8. At lower pH a variety of radical adducts are formed; at higher pH, the main product was the spin adduct of the formamide radical with tNB. The use of deuterated tNB and 15N-labeled potassium cyanide allowed the observation of the very small nitrogen coupling of this radical adduct. Experiments using 3,5-dibromo-4-nitrosobenzenesulfonic acid (DBNBS) as the spin trap yielded only the formamide radical adduct, which was identified by an independent synthesis starting from formamide. Both hydrogen splittings of its amino group could be resolved using deuterated DBNBS as the spin trap.
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PMID:Free radical intermediates formed during the oxidation of cyanide by horseradish peroxidase/H2O2 as detected with nitroso spin traps. 255 12

The mechanism of N-dealkylation by peroxidases of the Ca2+ indicator quin2 and analogs was investigated and compared with the mechanism of N-dealkylation of some N-methyl-substituted aromatic amines. Nitrogen-centered cation radicals were detected by ESR spectroscopy for all the compounds studied. Further oxidation of the nitrogen-centered cation radicals, however, was dependent upon the structure of the radical formed. In the case of quin2 and analogs, a carbon-centered radical could be detected using the spin trap 5,5-dimethyl-1-pyrroline N-oxide. By using the spin trap 2-methyl-2-nitrosopropane (tert-nitrosobutane), it was determined that the carbon-centered radical was formed due to loss of a carboxylic acid group. This indicated that bond breakage most likely occurred through a rearrangement reaction. Furthermore, extensive oxygen consumption was detected, which was in agreement with the formation of carbon-centered radicals, as they avidly react with molecular oxygen. Thus, reaction of the carbon-centered radical with oxygen most likely led to the formation of a peroxyl radical. The peroxyl radical decomposed into superoxide that was spin trapped by 5,5-dimethyl-1-pyrroline N-oxide and an unstable iminium cation. The iminium cation would subsequently hydrolyze to the monomethyl amine and formaldehyde. In the case of N-methyl-substituted aromatic amines, carbon-centered radicals were not detected during the peroxidase-catalyzed oxidation of these compounds. Thus, rearrangement of the nitrogen-centered radical did not occur. Furthermore, little or no oxygen consumption was detected, whereas formaldehyde was formed in all cases. These results indicated that the N-methyl-substituted amines were oxidized by a mechanism different from the mechanism found for quin2 and analogs.
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PMID:The oxidation of N-substituted aromatic amines by horseradish peroxidase. 255 33

Prostaglandin H synthase (PHS) hydroperoxidase-mediated metabolism of phenylbutazone and the relationship of this metabolism to the inhibition of PHS cyclooxygenase by phenylbutazone was investigated. Phenylbutazone was metabolized to several intermediates and metabolites. A phenylbutazone carbon-centered radical (aN = 14.6 G) formed by PHS hydroperoxidase was trapped by 2-methyl-2-nitrosopropane and detected by ESR in incubations with ram seminal vesicle microsomes. 4-Hydroperoxy- and 4-hydroxyphenylbutazone were isolated from incubations of phenylbutazone with either ram seminal vesicle microsomes or horseradish peroxidase. Phenylbutazone (100 microM-2 mM) inhibited PHS cyclooxygenase in incubations of PHS apoenzyme reconstituted with hematin. Phenylbutazone (5-250 microM) did not inhibit PHS cyclooxygenase in incubations of PHS apoenzyme reconstituted with manganese protoporphyrin IX, which lacks hydroperoxidase activity. Thus, metabolism of phenylbutazone by PHS hydroperoxidase is required for it to inhibit PHS cyclooxygenase. 4-Hydroperoxy- and 4-hydroxyphenylbutazone were ineffective inhibitors of PHS cyclooxygenase. Other hydroperoxides that easily rearrange to peroxyl radicals were potent inhibitors of PHS cyclooxygenase, suggesting that the phenylbutazone peroxyl radical may be the inhibitor. 4-Hydroperoxyphenylbutazone was not reduced to 4-hydroxyphenylbutazone by PHS hydroperoxidase. We propose that 4-hydroxyphenylbutazone formation occurs by a nonenzymatic reaction of two phenylbutazone peroxyl radicals and their subsequent rearrangement to alkoxy radicals, which abstract hydrogen atoms. Our data indicate the importance of PHS hydroperoxidase in the inactivation of PHS cyclooxygenase by peroxides.
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PMID:Prostaglandin hydroperoxidase-dependent oxidation of phenylbutazone: relationship to inhibition of prostaglandin cyclooxygenase. 284 54

A carbon-centered free radical formed during oxidative metabolism of 1,2-dimethylhydrazine has been spin-trapped with alpha-(4-pyridyl-1-oxide)N-tert-butyl nitrone and 2-methyl-2-nitrosopropane. In the horseradish peroxidase/H2O2 catalyzed oxidation, the trapped species was identified as the methyl radical by the characteristic 1:3:3:1 quartet pattern of the 2-methyl-2-nitroso propane adduct. A carbon-centered radical is also formed during microsomal oxidation of 1,2-dimethylhydrazine in the presence of NADPH. However, the alpha-(4-pyridyl-1-oxide)N-tert-butyl nitrone trapped radical has not been unambiguously identified in this latter instance. These results may be of importance in regard to both carcinogenic and antitumor properties of 1,2-disubstituted hydrazine derivatives.
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PMID:Spin-trapping of methyl radical in the oxidative metabolism of 1,2-dimethylhydrazine. 298 93

The iron chelator deferoxamine (Desferal; DSFL) reacts with peroxidases and H2O2 to form the DSFL radical (DSFL.), which can be detected by EPR spectroscopy. We have found that DSFL. formation resulting from exposure to H2O2 and any of a number of different peroxidases is greatly enhanced in the presence of the nitrone spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN). This enhancement was seen at 4-POBN concentrations as low as 200 microM. We observed a modest enhancement of DSFL. formation with 2-methyl-2-nitrosopropane. However, no enhancement was seen with 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) or phenyl-tert-butylnitrone. A modest enhancement was also seen with the nitrone compound pyridine N-oxide. 2-Methyl-2-nitrosopropane and pyridine N-oxide were additionally capable of increasing enzymatic peroxidase activity as measured by o-dianisidine and/or tetramethylbenzidine oxidation. Furthermore, at high concentrations of 4-POBN (50 mM) in the absence of DSFL, we detected a peroxidase/H2O2-dependent 12-line EPR spectrum that likely represents a 4-POBN/.4-POBN nitrogen-centered spin adduct. In the presence of both 4-POBN (10 mM) and DMPO (100 mM), an 18-line EPR spectrum was observed consistent with formation of a DMPO/.4-POBN nitrogen-centered spin adduct. Thus, the nitrone spin trap 4-POBN can enhance the peroxidase-mediated formation of DSFL., possibly via the formation of a transient 4-POBN radical species. These data suggest the importance of assessing the potential for nitrone spin traps to both inhibit and enhance biological oxidation prior to their use as potential pharmacological agents.
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PMID:The spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone stimulates peroxidase-mediated oxidation of deferoxamine. Implications for pharmacological use of spin-trapping agents. 749 57

Various mechanisms have been proposed for the reaction between heme proteins and organic hydroperoxides, including a peroxidase-type mechanism and homolytic cleavage. We used electron spin resonance (ESR) spectroscopy to investigate the formation of radicals in a hematin/tert-butyl hydroperoxide system. Spin trapping studies, using 5,5-dimethyl-1-pyrroline N-oxide (DMPO), showed the formation of peroxyl and alkoxyl radicals in this system. At higher hematin concentrations an alkyl radical adduct could also be detected, which was identified as the methyl radical by using the spin trap 2-methyl-2-nitrosopropane. Furthermore, the relative contribution of the peroxyl and alkoxyl radical adducts was determined at various DMPO concentrations using computer simulation. It was found that at low DMPO concentrations both the alkoxyl and the peroxyl radical adducts could be detected. At higher DMPO concentrations, on the other hand, the alkoxyl radical dominated, whereas the peroxyl radical adduct decreased to a small portion of the total radical adduct population. Thus, the alkoxyl radical was the initial radical, produced by homolytic scission of the O-O bond of the hydroperoxide by ferric hematin. Although some tert-butyl peroxyl radicals could be detected by direct ESR, the majority of the peroxyl radicals detected by spin trapping were methyl peroxyl radicals, formed in the reaction between methyl radicals (formed by beta-scission of the alkoxyl radicals) and oxygen.
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PMID:ESR spin trapping investigation of radical formation from the reaction between hematin and tert-Butyl hydroperoxide. 874 40

Phagocytes secrete the heme protein myeloperoxidase, which is present and active in human atherosclerotic tissue. These cells also generate hydrogen peroxide (H2O2), thereby allowing myeloperoxidase to generate a range of oxidizing intermediates and stable end products. When this system acts on L-tyrosine in vitro, it forms o, o'-dityrosine, which is enriched in atherosclerotic lesions. Myeloperoxidase, therefore, may oxidize artery wall proteins in vivo, cross-linking their L-tyrosine residues. In these studies, we used electron paramagnetic resonance (EPR) spectroscopy to identify an oxidizing intermediate in this reaction pathway and in parallel reactions catalyzed by horseradish peroxidase and lactoperoxidase. Using an EPR flow system to rapidly mix and examine solutions containing horseradish peroxidase, H2O2, and L-tyrosine, we detected free tyrosyl radical (a2,6H = 6.3 G, a3,5H = 1.6 G, and abetaH = 15. 0 G). We then used spin trapping techniques with 2-methyl-2-nitrosopropane (MNP) to further identify this intermediate. The resulting three-line spectrum (aN = 15.6 G) was consistent with an MNP/tyrosyl radical spin adduct. Additional MNP spin trapping studies with ring-labeled L-[13C6]tyrosine yielded a characteristic eight-line EPR spectrum (aN = 15.6 G, a13C (2) = 8.0 G, a13C (1) = 7.1 G, a13C (1) = 1.3 G), indicating that the MNP adduct resulted from trapping a carbon-centered radical located on the aromatic ring of L-tyrosine. This same eight-line spectrum was observed when human myeloperoxidase or bovine lactoperoxidase was substituted for horseradish peroxidase. Furthermore, a partially immobilized MNP/tyrosyl radical spin adduct was detected when we exposed a synthetic polypeptide composed of glutamate and L-tyrosine residues to the myeloperoxidase-H2O2-L-tyrosine system. The broadened EPR signal resulting from this MNP/polypeptide adduct was greatly narrowed by proteolytic digestion with Pronase, confirming that the initial spin-trapped radical was protein-bound. Collectively, these results indicate that peroxidases use H2O2 to convert L-tyrosine to free tyrosyl radical. They also support the idea that free tyrosyl radical initiates cross-linking of L-tyrosine residues in proteins. We suggest that this pathway may play an important role in protein and lipid oxidation at sites of inflammation and in atherosclerotic lesions.
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PMID:Electron paramagnetic resonance detection of free tyrosyl radical generated by myeloperoxidase, lactoperoxidase, and horseradish peroxidase. 982 76

Creatine kinase (CK) was used as a marker molecule to examine the side effect of damage to tissues by indomethacin (IM), an effective drug to treat rheumatoid arthritis and gout, with horseradish peroxidase and hydrogen peroxide (HRP-H2O2). IM inactivated CK during its interaction with HRP-H2O2. Under aerobic conditions, inactivation of CK significantly decreased. CK in rat heart homogenate was also inactivated by IM with HRP-H2O2. When IM was incubated with HRP-H2O2, the maximum absorption of IM at 280 nm rapidly decreased and a new peak at 410 nm occurred with isosbestic points at 260 and 312 nm. In contrast, under anaerobic conditions, the spectral change of IM was almost absent, indicating IM was oxidized to the yellow substance by HRP-H2O2. Adding catalase strongly inhibited the production of yellow substance. Sodium azide also blocked the formation of yellow substance and the inactivation of CK. Electron spin resonance signals of IM carbon-centered radical were detected using 2-methyl-2-nitrosopropane during the interaction of IM with HRP-H2O2 under anaerobic conditions. Oxygen was consumed during the interaction of IM with HRP-H2O2. These results suggest that IM carbon-centered radicals may rapidly react with O2 to generate the peroxyl radicals. Sulfhydryl groups and tryptophane residues of CK decreased during the interaction of IM with HRP-H2O2. Other sulfhydryl enzymes, including alcohol dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase, were also readily inactivated during the interaction with HRP-H2O2. Sulfhydryl enzymes seem to be very sensitive to IM activated by HRP-H2O2.
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PMID:Inactivation of creatine kinase during the interaction of indomethacin with horseradish peroxidase and hydrogen peroxide: involvement of indomethacin radicals. 1124 19

Creatine kinase (CK) was used as a marker molecule to examine the side effect of damage to tissues by phenylbutazone (PB), an effective drug to treat rheumatic and arthritic diseases, with horseradish peroxidase and hydrogen peroxide (HRP-H(2)O2). PB inactivated CK during its interaction with HRP-H(2) O(2), and inactivated CK in rat heart homogenate. PB carbon-centered radicals were formed during the interaction of PB with HRP-H(2)O2. The CK efficiently reduced electron spin resonance signals of the PB carbon-centered radicals. The spin trap agent 2-methyl-2-nitrosopropane strongly prevented CK inactivation. These results show that CK was inactivated through interaction with PB carbon-centered radicals. Sulfhydryl groups and tryptophan residues in CK were lost during the interaction of PB with HRP-H(2)O2, suggesting that cysteine and tryptophan residues are oxidized by PB carbon-centered radicals. Other enzymes, including alcohol dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, but not lactate dehydrogenase, were also inactivated. Sulfhydryl enzymes seem to be sensitive to attack by PB carbon-centered radicals. Inhibition of SH enzymes may explain some of the deleterious effects induced by PB.
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PMID:Phenylbutazone radicals inactivate creatine kinase. 1126 93


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