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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Some of the unusual molecular and catalytic properties of a high molecular weight dihydro-orotate dehydrogenase (DHOD) from Neurospora crassa have been determined. Comparison of the properties of this enzyme with the properties of the soluble biosynthetic enzyme of prokaryotes has revealed several important differences. The fungal enzyme is located in a mitochondrial membrane in a position consistent with linkage with the respiratory chain through ubiquinone (Miller, R. W.: Arch. Biochem, Biophys. 146, 256-270 (1971)). Release of the enzyme from the membrane results in a solubilized protein complex containing bound lipids and inactive hydrophobic proteins. Non-specific protein aggregation is minimized during purification by Triton-X-100 and phospholipase treatments. The catalytically active enzyme has an apparent molecular weight of 210 000. In contrast to soluble DHOD preparations the high molecular weight enzyme has no endogenous dihydro-orotate oxidase (EC 1.3.3.1) activity and is relatively insensitive to inactivation by sulfhydryl-reactive reagents in the presence of dihydro-orotate (DHO). The enzyme activity is highly sensitive to conditions causing oxidation of flavin mononucleotide (FMN). The activity cannot be restored by cysteine or other means. FMN is present in all purified preparations in a bound, non-fluorescent (reduced) form until dihydro-orotic acid is removed or oxidized. Catalytic efficiency of the purified enzyme was 12 000 mol DHO oxidized per minute per mole FMN. This high turnover rate is due in part to the small flavin content of the purified enzyme, equivalent to 1 mol FMN per 120 000 g of catalytically active protein. Iron was detected in the purified enzyme by atomic absorption spectroscopy but labile sulfide was absent. Thenoyltrifluoroacetone, an iron chelator, only partially inhibited DHO oxidation regardless of electron acceptor. Fatty acids interact with a hydrophobic site of the enzyme in non-competitive fashion but under certain conditions appear to significantly alter the Km for ubiquinone. Orotate, by comparison, is a purely competitive inhibitor. Both types of inhibitor may function to regulate the biosynthesis of orotate in vivo. Superoxide anion is not produced in significant quantities by the DHO-reduced enzyme unless both ubiquinone and a suitable single electron carrier such as phenazine methosulfate are present. DHOD has been proposed as a source of superoxide anion in mammalian mitochondria (Forman, H. J. & Kennedy, J. A.: J. Biol. Chem. 250, 4322-4326 (1975)).
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PMID:A high molecular weight dihydro-orotate dehydrogenase of Neurospora crassa. Purification and properties of the enzyme. 13 Jan 99

2-Nitropropane dioxygenase, purified to homogeneity from a yeast, Hansenula mrakii, is significantly inhibited by superoxide dismutase and various scavengers for superoxide anion such as cytochrome c, epinephrine, NADH, thiols, and polyhydric phenols. The reduction of cytochrome c and the oxidation of epinephrine and NADH are concomitant with the inhibition of enzymatic oxygenation. Neither the oxidation nor the reduction occursin the presence of superoxide dismutase or in the absence of 2-nitropropane or oxygen. Superoxide anion added externally induces the oxygenation. These findings indicate the generation of superoxide anion and its participation in the oxygenation of 2-nitropropane. The difference spectrum of the binding of NADH to 2-nitropropane dioxygenase exhibits a negative peak at 353 nm. One mole of NADH is bound to 1 mol of the enzyme and the pro-R hydrogen of the nicotinamide moiety of bound NADH predominantly is transferred to superoxide anion formed enzymatically or given externally. Thus, the diastereotopic hydrogen of NADH is discriminated by the enzyme, although not completely.
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PMID:Properties of 2-nitropropane dioxygenase of Hansenula mrakii. Formation and participation of superoxide. 20 19

The mechanism of inhibition of the veratryl alcohol oxidase activity of lignin peroxidase H2 (LiPH2) by EDTA was investigated. It was found that EDTA was decarboxylated and that cytochrome c, nitro blue tetrazolium, ferric iron, and molecular oxygen were reduced in a reaction mixture containing LiPH2, H2O2, veratryl alcohol, and EDTA. The reductive activity observed with LiPH2 followed first order kinetics with respect to the concentration of EDTA. Stoichiometry studies showed that in the presence of sufficient EDTA, 1.7 mol of ferric iron were reduced per mole of H2O2 added to the reaction mixture. Superoxide- and EDTA-derived radicals were detected by ESR spin trapping upon incubation of LiPH2 with H2O2, veratryl alcohol, and EDTA. The Km values of veratryl alcohol and H2O2 remained the same for both the oxidative and reductive activities of LiPH2. Reductive activity was also observed with LiPH2 and EDTA using other free radical mediators in the place of veratryl alcohol, such as 1,4-dimethoxybenzene, 1,2,3- and 1,2,4-trimethoxybenzenes, and 1,2,4,5-tetramethoxybenzene. EDTA reduced the cation radical of 1,2,4,5-tetramethoxybenzene formed by LiPH2 in the presence of H2O2. Hence, it is proposed that the apparent inhibition of the veratryl alcohol oxidase activity of LiPH2 by EDTA is due to the reduction of the veratryl alcohol cation radical intermediate back to veratryl alcohol by EDTA. The reduction of cytochrome c, nitro blue tetrazolium, ferric ion, and molecular oxygen appears to be mediated by the EDTA radical formed by reduction of the veratryl alcohol cation radical.
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PMID:On the mechanism of inhibition of the veratryl alcohol oxidase activity of lignin peroxidase H2 by EDTA. 132 38

The reason for the differences in phototoxic potential between the 5 quinolone antibacterial agents lomefloxacin, enoxacin, ciprofloxacin, ofloxacin and DR-3355 (the s-isomer of ofloxacin) in mice was investigated. Superoxide anion, hydrogen peroxide (H2O2), and bleaching of p-nitrosodimethylaniline (B-NDMA) were detected in quinolone solutions during irradiation with ultraviolet-A (UVA). Apparent levels of H2O2 and the B-NDMA per mole of quinolone paralled the phototoxic potentials in the mice. The N-NDMA induced by quinolones and UVA was inhibited partially by treatment with D-mannitol and dimethylsulfoxide, and also with diethylenetriamine-pentaaceticacid (DTPA), suggesting that Haber-Weiss and Fenton reactions occurred. UVA concentration-dependently increased the level of the B-NMDA in H2O2 solution and the swelling in the ear pretreated by intra-auricular injection of H2O2. Both augmentations were inhibited by DTPA or DMSO. The swelling induced by the 5 quinolones and UVA was completely inhibited by pretreatment with dimethylsulfoxide. Oxygen consumption was detectable during the photodegradation, and increased with time. These results showed that the phototoxic potentials of the 5 quinolones were probably related to the amounts of toxic oxygens generated in the target cells during irradiation.
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PMID:Possible reasons for differences in phototoxic potential of a 5 quinolone antibacterial agents: generation of toxic oxygen. 133 37

Pig alveolar macrophages generate superoxide anions at a rate of 1.8 nanomoles/1 X 10(6) cells/min. The intracellular value of ATP in resting cells was 4.0 +/- 0.1 X 10(-16) mole/cell; in contrast the value in cells generating superoxide anions was 2.0 +/- 0.6. Superoxide generation was increasingly inhibited by exposing cells to adenosine from 0.1 to 1.0 mM. Unlike human macrophages, pig cell production of superoxide anions was not inhibited by exposure to the adenosine analog, 2-Cl-adenosine.
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PMID:Superoxide generation by pig alveolar macrophages. 302 88

Superoxide, generated by a xanthine oxidase/hypoxanthine system, reacts with reduced glutathione (GSH) to cause an increase in oxygen consumption and oxidized glutathione (GSSG) formation, both of which are fully inhibited by superoxide dismutase. In this study we have shown that little, if any, of the additional oxygen consumed is converted to hydrogen peroxide. We have confirmed that approximately 90% of the GSH is oxidized to GSSG, the remainder being converted to the sulfonic acid. Approximately 1.2 mol of GSSG was formed for each additional mole of oxygen consumed in the presence of GSH. The efficiency of the reaction increased with increasing GSH concentration (1-8 mM), pH, and pO2 and with decreasing superoxide generation rate. The results are consistent with a superoxide-dependent chain that does not produce hydrogen peroxide and that is terminated primarily by superoxide dismutation. We propose that this occurs via an initial reaction of superoxide with GSH to produce a sulfinyl radical rather than hydrogen transfer to give the thiyl radical. Our data suggest a rate constant for the superoxide/GSH reaction in the 10(2)-10(3) M-1s-1 range. GSH at the millimolar concentrations found intracellular should react with superoxide, but because superoxide is regenerated, it will not be an effective scavenger. Physiologically, superoxide dismutase is required to prevent chain oxidation of GSH.
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PMID:The reaction of superoxide with reduced glutathione. 797 67

The chain-breaking antioxidant potential of caeruloplasmin and bovine serum albumin (BSA) has been investigated in comparison with other well-established antioxidants. Their Oxygen Radical Absorbing Capacity (ORAC), was measured by using beta-phycocyanin (beta-PC) as a fluorescent indicator protein, 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH) as a peroxyl radical generator and the water soluble vitamin E analogue, Trolox, as a reference standard. The relative peroxyl absorbing capacities/mole for Trolox, caeruloplasmin, heat-denatured caeruloplasmin (hCP), catalase, bovine serum albumin (BSA), superoxide dismutase (SOD), and deferoxamine were 1; 2.6; 3.3; 3.7; 1.2; 0.1; 0.2, respectively. Caeruloplasmin was far more effective as a peroxyl radical scavenger than SOD, deferoxamine and BSA, but slightly less effective than catalase. The peroxyl radical absorbing capacity of caeruloplasmin was enhanced by heat-denaturation of the protein. Electron paramagnetic resonance (EPR) spectroscopy using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin-trap, was applied in order to measure the scavenger abilities of caeruloplasmin on superoxide radical and hydroxyl radical production and the concentration required to inhibit by 50% oxygen free radical formation (IC50) was determined. The IC50 values of caeruloplasmin, hCP, and BSA for the superoxide radical were 12, 2, 260 microM and for the hydroxyl radical 15, 2, 200 microM. These results show that caeruloplasmin is an effective chain-breaking antioxidant for a variety of radicals, independently of its catalytic ferroxidase activity.
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PMID:Direct evidence of caeruloplasmin antioxidant properties. 987 63

The abiotic transformation of catechol and 1-naphthol singly and in mixtures was tested in sterile Tris-HCl buffer with regard to several environmental factors including temperature (7 degrees C, 20 degrees C and 30 degrees C), lighting conditions, pH (between 7.0 and 8.5) and dissolved oxygen (at partial pressures of 0.0, 220, 2200, 11000 and 22000 Pa). Irrespective of lighting conditions. catechol autoxidation was confirmed in aerated medium with a rate independent of the presence of 1-naphthol but proportional to the dissolved oxygen concentration, to the pH (its half-disappearance occurred in 24h at pH 8.5) and, to a lesser extent, to the incubating temperature (at 20 degrees C, 20% disappeared in 10 days at pH 7.0). Under alkaline conditions, the reaction of the anionic form (catecholate) with an equimolar concentration of molecular oxygen (O2) led presumably to hydrogen peroxide anion (HO2-) and coloured polymerization products. When tested alone, 1-naphthol was not significantly influenced either by lighting conditions, incubating temperature or dissolved oxygen concentration. It was also found to be quite stable with respect to pH, with a 15-fold weaker transformation rate than for catechol at the highest pH used. When tested in a mixture with catechol, 1-naphthol was found to be involved in a new chemical oxidation reaction catalyzed by catecholate. The transformation of one mole of 1-naphthol consumes four moles of oxygen. In the presence of catechol, the stoichiometry of the 1-naphthol transformation, under the influence of oxygen, suggests the possible formation of 2,5,6,8-tetrahydroxy 1,4-naphthoquinone via Lawsone (2-hydroxy 1,4-naphthoquinone) and naphthopurpurine (2,5,8-trihydroxy 1,4-naphthoquinone) as hypothetic intermediates. This is the first report of the autoxidation of 1-naphthol, catalyzed by catechol, in aqueous solution, in the absence of UV irradiation.
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PMID:Abiotic transformation of catechol and 1-naphthol in aqueous solution-influence of environmental factors. 1156 36

We present a direct ab initio dynamics study on the hydrogen abstraction reaction CH2O + HO2 --> CHO + H2O2, which is predicted to have four possible reaction channels caused by different attacking orientations of HO2 radical to CH2O. The structures and frequencies at the stationary points and the points along the minimum energy paths (MEPs) of the four reaction channels are calculated at the B3LYP/cc-pVTZ level of theory. Energetic information of stationary points and the points along the MEPs is further refined by means of some single-point multilevel energy calculations (HL). The rate constants of these channels are calculated using the improved canonical variational transition-state theory with the small-curvature tunneling correction (ICVT/SCT) method. The calculated results show that, in the whole temperature range, the more favorable reaction channels are Channels 1 and 3. The total ICVT/SCT rate constants of the four channels at the HL//B3LYP/cc-pVTZ level of theory are in good agreement with the available experiment data over the measured temperature ranges, and the corresponding three-parameter expression is k(ICVT/SCT) = 3.13 x 10(-20) T(2.70) exp(-11.52/RT) cm3 mole(-1) s(-1) in the temperature range of 250-3000 K. Additionally, the flexibility of the dihedral angle of H2O2 is also discussed to explain the different experimental values.
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PMID:Direct dynamics study on the hydrogen abstraction reaction CH2O + HO2 --> CHO + H2O2. 1636 58

The experimental study of the oxidation of the three linear isomers of hexene was performed in a quartz isothermal jet-stirred reactor (JSR) at temperatures ranging from 500 to 1100 K including the negative temperature coefficient (NTC) zone, at quasi-atmospheric pressure (1.07 bar), at a residence time of 2 s and with dilute stoichiometric mixtures. The fuel and reaction product mole fractions were measured using online gas chromatography. In the case of 1-hexene, the JSR has also been coupled through a molecular-beam sampling system to a reflectron time-of-flight mass spectrometer combined with tunable synchrotron vacuum ultraviolet photoionization. A difference of reactivity between the three fuels, which varies with the temperature range has been observed and is discussed according to the changes in the possible reaction pathways when the double bond is displaced. An enhanced importance of the reactions via the Waddington mechanism and of those of allylic radicals with HO2 radicals can be noted for 2- and 3-hexenes compared to 1-hexene.
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PMID:Products from the oxidation of linear isomers of hexene. 2440 Jun 65


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