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Query: UNIPROT:P06889 (Mol)
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(1) 45% of the total copper of green zucchini ascorbate oxidase is EPR-detectable. At least two species of copper are present, one with a small A parallel (Type 1) and one with a large A parallel (Type 2). Computer simulated spectra indicated 50% contribution by each type of copper. (2) Azide inhibited ascorbate oxidase activity by an uncompetitive mechanism. EPR and optical spectra performed on titration of ascorbate oxidase with azide indicated the formation of a copper-azide complex. The Type 2 copper appears to be the binding site of azide. The involvement of the EPR non-detectable copper as an anion binding site with high affinity toward azide can not be excluded.
Mol Cell Biochem 1975 May 30
PMID:The effect of azide on the spectral and catalytic properties of ascorbate oxidase. 16 78

The interaction of nitrogenase with spin labels of four types have been studied. Conclusion about the presence of two SH-groups in the nitrogenase active site (one in Mo-Fe-protein and one in the Fe-protein) have been drawn from the correlation between the degree of inhibition of nitrogenfixing activity by the labels derived from p-Cl-Hg-benzoate and degree of binding of these labels to the nitrogenase molecule. Anaysis of EPR spectra of spin-labeled nitrogenase at 77 degrees K and at room temperature have shown that the labels bind to the free SH-groups and interact with iron containing center (ICC) of nitrogenase through the exchange mechanism. Distance between SH-group and ICC have been found to be 12 A. Spin labels derived from isocyanide have been bound directly to ICC in amount of 6--10 labels per one nitrogenase molecule. Due to the exchange interaction between these labels they give the singlet ESR spectra both at 77 degrees and at room temperature which is characteristic for the closely disposed labels. From this fact a conclusion have been drawn about the cluster structure of ICC. The labels derived from iodoacetamide ana maleimide bind SH- and NH2-groups of nitrogenase molecules. Analysis of temperature dependence of the effective rotational frequency of this labels have revealed a conformational transition in nitrogenase molecule at 19 degrees C, that has made it possible to explain the break in the Arrenius plots of enzyme activity.
Mol Biol (Mosk)
PMID:[Study of the nitrogenase from Azotobacter vinelandii by the method of spin labels]. 17 70

A new method of estimation of the distance between spins of the spin-label and paramagnetic center is suggested. Method is based on the quantitative analys of saturation curve of spin-label EPR spectra at 77 degrees K. New approaches have been tested using haemoglobin labeled on SH-groups with various iminoxyl radicals. Values of the distances between labels and haem estimated from the saturation curve parameters and by current methods and values of distances estimated from X-ray data are in good agreement. In the case of rapid spin relaxation of he paramagnetic center, the new method allows one to determine a farther distance. Results of the present work make it possible to investigat by the spin-label technique the structure of haem-containing propeins and the structure of other proteins with known spin relaxation time of paramagnetic center.
Mol Biol (Mosk)
PMID:[Determination of the distance between spin labels and the paramagnetic center in spin-labeled proteins according to parameters of the saturation curves of the label EPR spectra at 77 degrees K]. 18 3

The surface of liposomes and natural membranes has been studied by the method of "spin label--spin probe". Various nitroxyl radicals have been attached to membranes either dueto covalent binding with NH2-groups of phosphatidylethanolamine or due to hydrophobic interactions. Addition of paramagnetics of different charge signs (potassium ferricyanide and dibenzenechromium iodide) to spin labeled membranes results in a decrease of the EPR line intensity without marked broadening. Since the paramagnetic is attached to the membrane surface near the label it broadens the label's EPR spectrum so that it can not be observed. In this case one can observe only the spectrum of labels which have no paramagnetics in the vicinity, the nitroxyl part of radicals being inaccessible to direct paramagnetic impacts. The constants of binding of paramagnetics to the membrane surface have been determined from these experiments. All results (including the assymetry of label rotation) can be explained most simply by assuming that the polar lipid groups are oriented parallel to the membranes surface.
Mol Biol (Mosk)
PMID:[Spin label study of the surface of lipid bilayers]. 20 76

The sensitivity of the molybdenum-iron(MoFe)-protein of Clostridium pasteurianum nitrogenase toward oxidation has been studied by determining the enzymatic activity of this component after incubating it anaerobically in ferricyanide solutions of various oxidizing strengths (as measured by their oxidation potentials). It was found that the MoFe-protein remains active at potentials up to +350 mV (vs. standard hydrogen electrode) but becomes readily inactivated at more oxidizing potentials, after a lag period, depending on the potential level and temperature. Oxidative inactivation by ferricyanide results in the release of most of the Mo, Fe and S atoms from the protein which causes the loss of the absorption bands in the visible region. The metals and sulfur could be re-incorporated by incubation in a mixture containing thiol, sulfide, molybdate, and ferric iron. The EPR spectrum of the oxidatively inactivated MoFe-protein showed that both the high- and low-field signals are readily affected. Re-incorporation of the metals and sulfur into the "bleached" protein produced an EPR spectrum similar to that of the air-inactivated protein. Incubation of the Mo-Fe-protein with mersalyl abolished its enzymic activity. The difference spectrum before and after mersalyl treatment resembles that of the soluble spinach ferredoxin.
Mol Cell Biochem 1979 Jul 31
PMID:Oxidative inactivation of the molybdenum-iron-protein component of nitrogenase from clostridium pasteurianum. 22 73

Two radical adduct species have been detected in the bile of living rats treated with halothane and phenyl-N-t-butylnitrone (PBN). The treatment of rats with 12% oxygen was required for radical adduct detection. Analysis of the corresponding EPR spectra obtained when deuterated PBN and deuterated halothane or [2-13C]halothane was used shows that these two species result from the spin trapping of two halothane-derived free radicals. Coupling constants were aN = 15.72 G, a beta H = 2.09 G, a gamma H = 0.79 G, and aF = 0.63 G(3F) and aN = 15.16 G, a beta H = 4.14 G, a gamma H = 0.48 G, and aF = 0.3 G(3F) for the two species. Two radical adducts with similar coupling constants were detected when halothane was reduced by zinc dust in the presence of PBN, suggesting that the formation of these two distinct species from halothane can be attributed to the one-electron reduction of halothane and the formation of diastereomeric radical adducts. The identification of both radical adducts as halothane-derived species indicates that there is no in vivo EPR evidence for lipid radical formation during halothane intoxication, as had previously been reported.
Mol Pharmacol 1992 May
PMID:Free radical metabolism of halothane in vivo: radical adducts detected in bile. 131 2

Lidocaine, a local anaesthetic, has been shown to reduce ventricular arrhythmias associated with myocardial infarction and ischemic myocardial injury and its protective effects has been attributed to its membrane stabilizing properties. Since oxygen radicals are known to be produced during ischemia induced tissue damage, we have investigated the possible antioxidant properties of lidocaine and found that lidocaine does not scavenge O2-. radicals at 1 to 20 mM concentrations. However, lidocaine was found to be a potent scavenger of hydroxyl radicals and singlet oxygen. Hydroxyl radicals were produced in a Fenton type reaction and detected as DMPO-OH adducts by electron paramagnetic resonance spectroscopic techniques. Lidocaine inhibited DMPO-OH adduct formation in a dose dependent manner. The amount of lidocaine needed to cause 50% inhibition of that rate was found to be approximately 80 microM and at 300 microM concentration it virtually eliminated the DMPO-OH adduct formation. The production of OH.-dependent TBA reactive products of deoxyribose was also inhibited by lidocaine in a dose dependent manner. Lidocaine was also found to inhibit the 1O2-dependent 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO) formation in a dose dependent manner. 1O2 was produced in a photosensitizing system using Rose Bengal or Methylene Blue as photosensitizers and was detected as TEMP-1O2 adduct by EPR spectroscopy. The amount of lidocaine required to cause 50% inhibition of TEMP-1O2 adduct formation was found to be 500 microM. These results suggest that the protective effect of lidocaine on myocardial injury may, in part, be due to its reactive oxygen scavenging properties.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Cell Biochem 1992 Oct 07
PMID:Lidocaine: a hydroxyl radical scavenger and singlet oxygen quencher. 133 38

We examined the effects of cholesterol on the membrane-disordering action of ethanol by using deuterium nuclear magnetic resonance (2H-NMR) and fluorescence spectroscopy. Specifically, the effects of ethanol were measured on the 2H-NMR spectra of di(perdeuteropalmitoyl)phosphatidylcholine (DPPC-d62) and on the steady-state emission anisotropy of diphenylhexatriene (DPH) incorporated into hydrated egg phosphatidylcholine (eggPC)/cholesterol dispersions. Analysis of the 2H-NMR spectra of DPPC-d62 incorporated into eggPC liposomes showed that the addition of cholesterol up to 30 mol% enhanced the ability of ethanol to disorder methylene groups all along the phospholipid acyl chains. This effect was somewhat greater toward the terminal methyl groups. However, above 30 mol% cholesterol, the bilayer-disordering action of ethanol on both the upper and lower portions of the acyl chains decreased to an apparent constant change up to the highest cholesterol content examined (50 mol%). Analysis of the fluorescence anisotropy of DPH, on the other hand, suggested that cholesterol attenuated the ability of ethanol to disorder the bilayers, which is in agreement with a previous EPR study [Chin and Goldstein, Mol Pharmacol 19: 425-431, 1981]. Re-analysis of our previous fluorescence anisotropy results with DPH incorporated into dispersions of brain-lipid extracts as a percent change [Johnson et al., Mol Pharmacol 15: 739-746, 1979] indicated that the chemical composition of the lipid bilayers also affects the apparent ability of cholesterol to modulate the membrane-disordering action of ethanol, because the addition of cholesterol to brain-lipid extracts had no significant effect on the membrane-disordering action of ethanol. Given the greater likelihood that the 2H-NMR probes accurately monitor bulk phospholipid properties, some caution is required in the analysis of the membrane-disordering actions of drugs using EPR and fluorescence spectroscopy.
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PMID:A deuterium NMR and steady-state fluorescence anisotropy study of the effects of cholesterol on the lipid membrane-disordering actions of ethanol. 151 Jul 24

Nifedipine [1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridinedicarboxylic+ ++ acid dimethyl ester] and nimodipine [1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylic+ ++ acid 2-methoxyethyl 1-methylethyl ester], incorporated into diheptanoylphosphatidylcholine liposomes, which were used as a drug carrier system, slightly inhibited lipid peroxidation (induced by tert-butylhydroperoxide and Fe2+) in rat heart homogenate. Illumination of nimodipine had no effect on its antioxidant potency, whereas illuminated nifedipine was several times more effective than nonilluminated drug. On illumination, nifedipine converts to 2,6-dimethyl-4-(2-nitrosophenyl)-3,5-pyridinedicarboxylic acid dimethyl ester (NTP). NTP formed stable radicals when interacting with the rat heart homogenate and dioleoylphosphatidylcholine, as detected by EPR spectroscopy. No radical formation was observed if nonilluminated nifedipine and nimodipine or illuminated nimodipine were used. The spin density of the unpaired electron in the NTP-adduct was centered on the nitrogen derived from its nitroso group. The motion of the NTP-adduct radical was restricted, indicating that the radicals were located in the membrane of the homogenate and not in the buffer system. Only NTP (not nifedipine or nimodipine) was effective in trapping free radicals formed by the thermal or photoinduced decomposition of 2,2'-azobisisobutyronitrile and radicals formed by photolysis of di-tert-butylperoxide. The antioxidant and spin-trapping properties of NTP in our systems were attributed to its nitroso group.
Mol Pharmacol 1991 Sep
PMID:Spin-trapping and antioxidant properties of illuminated and nonilluminated nifedipine and nimodipine in heart homogenate and model system. 165 16

The drug SR 4233 (3-amino-1,2,4-benzotriazine 1,4-dioxide) is under pharmacological study as the lead compound in a new series of hypoxia-activated drugs, the benzotriazine N-oxides. However, the stable two- and four-electron-reduced metabolites of SR 4233, formed by the successive loss of the two oxygen atoms, are not pharmacologically active. In order to evaluate the possibility of an initial one-electron intermediate as the active species, we have used microsomal reduction and EPR spectroscopy to identify the first free radical reduction product. The unpaired electron is primarily centered on the 1-nitrogen, and the radical is best described as a nitroxide. Results with spin-trapping experiments show that reduction of SR 4233 to a free radical is followed by its air oxidation, resulting in the formation of the superoxide radical. Experiments with specific inhibitors suggest that the drug is being reduced by microsomal NADPH-cytochrome P-450 reductase.
Mol Pharmacol 1991 Sep
PMID:Microsomal reduction of 3-amino-1,2,4-benzotriazine 1,4-dioxide to a free radical. 165 17


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