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S D Aust

Publications and source records attributed to S D Aust.

At least 91 records · Page 5Linked to original sources
PubMed1993

Plasma membrane dependent reduction of 2,4,6-trinitrotoluene by Phanerochaete chrysosporium.

A plasma membrane redox system of Phanerochaete chrysosporium was found to reduce 2,4,6-trinitrotoluene (TNT). Reduction required intact, live mycelia. No reduction was observed with either supplemented (NADPH, NADH or ATP) or unsupplemented extracellular or intracellular fractions, either under aerobic or anaerobic conditions. Reduction was inhibited by potassium ferricyanide, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium, carbonyl cyanide p-trifluoromethoxyphenyl hydrazone, 2,4-dinitrophenol, sodium azide, and tetranitroblue tetrazolium but not by nitroblue tetrazolium, 2,3,5-triphenyl tetrazolium and blue tetrazolium. At higher pH, the rate of reduction as well as proton pumping was enhanced.

Basidiomycota↗
PubMed1993

Metabolism and detoxification of TNT by Phanerochaete chrysosporium.

Several lines of evidence suggest that TNT detoxification by Phanerochaete chrysosporium is through reduction. Rates of TNT reduction were directly correlated with mycelial mass and TNT concentration. Toxicity was inversely related to the amount of fungus. TNT toxicity was identical in both ligninolytic and nonligninolytic cultures. Rapid disappearance of the reduced metabolites coincided with production of the manganese-dependent peroxidases and mineralization of TNT was not observed until the lignin peroxidases were detected.

Basidiomycota↗
PubMed1993

Iodide as the mediator for the reductive reactions of peroxidases.

Lignin peroxidase H2 (LiPH2) from the white rot fungus Phanerochaete chrysosporium catalyzed the reduction of cytochrome c, nitro blue tetrazolium, ferric iron, molecular oxygen, and triiodide in a reaction mixture containing LiPH2, H2O2, EDTA, and iodide. Activity followed first order kinetics with respect to EDTA concentration. The reductive activity observed with LiPH2 using iodide as the mediator was comparable to that obtained using a variety of other free radical mediators such as veratryl alcohol, 1,4-dimethoxybenzene, and 1,2,3- and 1,2,4-trimethoxybenzene. EDTA-derived radicals were detected by ESR spin trapping upon incubation of LiPH2 with H2O2, iodide, and EDTA. Reduction activity was also observed using other peroxidases such as lactoperoxidase, horseradish peroxidase, and myeloperoxidase. For the reduction activity of LiPH2, it is proposed that the oxidation of EDTA is mediated by the iodide radical, and the reduction of various electron acceptors is mediated by EDTA radicals. The inhibition of reduction activity at higher concentrations of iodide might be due to the combination of iodide radicals to form I2 which forms a stable triiodide complex by reacting with excess iodide.

Basidiomycota↗
PubMed1993

Reduction of CCl4 to the trichloromethyl radical by lignin peroxidase H2 from Phanerochaete chrysosporium.

We were able to spin trap the trichloromethyl radical with PBN in a reaction mixture containing lignin peroxidase H2, H2O2, CCl4, veratryl alcohol and EDTA. Upon removal of CCl4, EDTA radicals were detected. Based on a previously reported study (Shah et al., 1992, J. Biol. Chem. 267, 21564-21569), we propose that the oxidation of EDTA to EDTA derived radicals is mediated by the veratryl alcohol cation radical, and the reduction of CCl4 to the trichloromethyl radical is caused by the EDTA derived radicals. The novel finding here is that CCl4, which is neither a substrate for the enzyme nor a good reductant, is degraded via free radicals generated by lignin peroxidases under reducing conditions.

Carbon Tetrachloride↗
PubMed1993

Xanthine oxidase- and iron-dependent lipid peroxidation.

Xanthine oxidase and iron-dependent lipid peroxidation has been studied extensively in many model systems, yet several details of this process remain unclear. Because redox reactions of iron are important parameters of iron-catalyzed lipid peroxidation, we have examined the roles of superoxide and hydrogen peroxide, produced by xanthine oxidase, to oxidize and reduce iron and thereby affect iron-catalyzed lipid peroxidation. Thus, we compared lipid peroxidation catalyzed by xanthine oxidase and ADP:Fe(III) to that catalyzed by xanthine oxidase and ADP:Fe(II). An examination of the action of superoxide on iron oxidation and reduction revealed that superoxide is a better oxidant of ADP:Fe(II) than a reductant of ADP:Fe(III). A superoxide generating system (composed of xanthine oxidase and catalase) and ADP:Fe(II) also resulted in a greater amount of lipid peroxidation than superoxide and ADP:Fe(III). Hydrogen peroxide, as expected, only served as an Fe(II) oxidant. A comparison of the oxidant activities of either superoxide or hydrogen peroxide on ADP:Fe(II) and the corresponding effects on lipid peroxidation revealed that both oxidants were roughly equivalent. We conclude that superoxide and hydrogen peroxide, produced from xanthine oxidase, support iron-catalyzed lipid peroxidation through their participation in redox reactions of iron, that is, they facilitate Fe(II) oxidation or Fe(III) reduction necessary for lipid peroxidation. The relevance of the reactions of O2-. and H2O2 on physiological chelates of iron are discussed.

Adenosine Diphosphate↗
PubMed1993

Veratryl alcohol-dependent production of molecular oxygen by lignin peroxidase.

Veratryl alcohol- and H2O2-dependent production of oxygen by lignin peroxidase isozyme H2 (LiPH2) from Phanerochaete chrysosporium was investigated. Veratryl alcohol oxidation by LiPH2 decreased with increasing concentrations of H2O2 while oxygen evolution increased. The absorption spectrum of the LiPH2 in these experiments indicated that it was in the compound II state. We propose that O2 production results from the one electron oxidation of H2O2 by the veratryl alcohol cation radical to yield superoxide, as the addition of superoxide dismutase stimulated oxygen production. It has been reported previously that oxygen is consumed in reaction mixtures containing lignin peroxidase, H2O2, veratryl alcohol, and oxalate (Popp, J. L., Kalyanaraman, B., and Kirk, T.K. (1990) Biochemistry 29, 10475-10480). In the presence of oxalate, we observed oxygen consumption that was dependent on the H2O2 concentration. The ability of other methoxybenzenes to mediate oxygen production appeared to be related to their redox potential. It was concluded that cation radicals can oxidize H2O2 by one electron which results in the production of superoxide and the evolution of molecular oxygen. Thus, the rates of LiPH2-catalyzed O2 consumption or O2 production are dependent on the relative concentrations of H2O2 and oxalate.

Agaricales↗
PubMed1993

The role of metals in the enzymatic and nonenzymatic oxidation of epinephrine.

The effects of transition metals on nonenzymatic and ceruloplasmin catalyzed epinephrine oxidation were investigated by studying rates of epinephrine oxidation in purified buffers and in the presence of metal chelating agents. We found that epinephrine does not "autoxidize" in sodium chloride solutions prepared with deionized water that was further purified by chromatography over Chelex 100 resin prior to use. Epinephrine was oxidized rapidly in sodium chloride prepared with tap water (1.20 +/- 0.12 nmoles/min) or in deionized water (0.40 +/- 0.80 nmoles/min), but this oxidation was prevented by the addition of Desferal, a potent metal chelating agent. Epinephrine oxidation was enhanced upon the addition of ceruloplasmin, and this oxidation rate could be slowed, but not eliminated, by the addition of Desferal. If epinephrine solutions were preincubated for 72 hours with Desferal prior to ceruloplasmin addition, however, no oxidation was observed. Epinephrine was shown to form colored complexes with both iron and copper at pH 7.0. The Fe(III)-epinephrine complex was much more stable than was the Cu(II)-epinephrine complex. Oxygen consumption studies of ceruloplasmin catalyzed epinephrine oxidation showed that copper was a better promoter of epinephrine oxidation than was iron, suggesting that ceruloplasmin-catalyzed epinephrine oxidation results from adventitious copper bound to the purified enzyme. In light of these results, the physiological relevance of ceruloplasmin catalyzed oxidation of biogenic amines may be minor.

Biogenic Monoamines↗
PubMed1993

Oxidation of halides by peroxidases and their subsequent reductions.

The iodide oxidase activity and iodide-dependent pseudocatalatic activity of lignin peroxidase H2, an extracellular enzyme of the white rot fungus Phanerochaete chrysosporium, was inhibited by EDTA. The inhibition of iodide oxidase activity by EDTA was reversed at higher concentrations of iodide. Similar results were observed with a number of peroxidases. On further investigation, it was found that EDTA was decarboxylated in a reaction mixture containing a peroxidase, iodide, H2O2, and EDTA. EDTA was also decarboxylated by hypoiodite, a possible intermediate during oxidation of iodide by peroxidases. Iodide-dependent pseudocatalatic activity was increased with an increase in the concentration of H2O2 and inhibited at higher concentrations of iodide. EDTA was also oxidized by horseradish peroxidase, lactoperoxidase, and myeloperoxidase using iodide or bromide as a mediator. However, only myeloperoxidase was able to decarboxylate EDTA using chloride as a mediator. It is proposed that halide is oxidized to hypohalite by peroxidases. The hypohalite is then reduced by EDTA, H2O2, or halide. Reduction is associated with the decarboxylation of EDTA, oxidation of H2O2 to molecular oxygen, or oxidation of halide.

Agaricales↗
PubMed1993

On the mechanism of peroxidase-catalyzed oxygen production.

A mechanism for oxygen production involving the reaction of cation radicals with H2O2 was investigated. The rate of oxygen production by peroxidases was greatly enhanced by the addition of ABTS [2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid)] or chlorpromazine, both of which are oxidized to cation radicals by peroxidases. We propose that enhanced oxygen evolution is due to the reaction of the cation radicals of these compounds with H2O2 to produce O2-. which then dismutates to produce oxygen. Oxygen evolution was quantitated in reaction mixtures containing electrochemically generated ABTS cation radicals and H2O2. The reaction was found to be first order with respect to the concentrations of the ABTS cation radical and H2O2 and the rate constants indicated that O2-. was an intermediate. Ferric EDTA enhanced oxygen production in both reaction systems (i.e., using ABTS+. that was generated electrochemically or with a peroxidase). These results suggest that O2-. production catalyzed by peroxidases is dependent upon a compound which is oxidized by the peroxidase to a cation radical. Superoxide is subsequently produced from the one-electron oxidation of H2O2 by the cation radical.

Benzothiazoles↗
PubMed1993

Relationship between iron and phosphate in mammalian ferritins.

The core of mammalian ferritin is known to contain varying amounts of phosphate as well as iron. This study examined the variations in phosphate found in ferritins from horse spleen, rat liver, and bovine liver. The amount of phosphate varied inversely with the amount of iron present in the core. Theoretical extrapolation showed that in the absence of phosphate approximately 4400 atoms of iron could be incorporated into ferritin. Reconstitution of ferritin with iron and ceruloplasmin followed by prolonged incubation with phosphate produced cores similar to native ferritin in terms of iron to phosphate ratios and rates of iron release. However, ferritin reconstituted in the presence of phosphate differed markedly from native ferritins. The data suggest that phosphate is an integral part of mammalian ferritin cores and influences both core formation and the ease by which iron is released from ferritin.

Animals↗
PubMed1993

Reductive activity of a manganese-dependent peroxidase from Phanerochaete chrysosporium.

A manganese-dependent peroxidase (MnP) from Phanerochaete chrysosporium catalyzed the reduction of cytochrome c in a reaction mixture containing H2O2, Mn(II)-tartrate, and p-hydroquinone. Electron spin resonance studies have shown that the hydroquinone-dependent reductive activity of MnP is due to the benzosemiquinone formed upon the one-electron oxidation of p-hydroquinone by Mn(III)-tartrate, which is formed upon the oxidation of Mn(II) by MnP. The reductive activity increased linearly with an increase in the concentration of p-hydroquinone. The reductive activity was also observed using other hydroquinones such as methylhydroquinone, 2,5-dimethylhydroquinone, and trimethylhydroquinone. The apparent Km values for Mn(II) and H2O2 for the hydroquinone-dependent reductive activity were similar to those for oxidative reactions of MnP. A stoichiometry study showed that about 1.5 mol of cytochrome c was reduced per mole of H2O2 consumed. The stoichiometry decreased with an increase in the concentration of H2O2. The optimal pH for the reductive activity was 5.0, approximately the physiological pH of the fungus. The reduction of cytochrome c was also observed using a quinone and cellobiose:quinone oxidoreductase isolated from the extracellular medium of the fungus.

Basidiomycota↗
PubMed1993

Free radicals in toxicology.

Free radicals are recognized more and more frequently as being involved in the mechanism of toxicity of chemicals. In some cases, the organic radicals are involved, but often oxygen radicals result from redox cycling chemicals. Free radicals are usually very reactive, which, in addition to causing toxicities, can make them difficult to detect. Electron spin resonance (ESR) techniques are frequently used, but generally the radicals must be trapped to form a more stable radical for detection. Quantitation is therefore often very difficult. Free radicals of many xenobiotics are formed during their metabolism by enzymes such as cytochrome P450 or peroxidases. In some cases, chemicals can redox cycle using reductases, such as cytochrome P450 reductase, which can catalyze one-electron reductions. Some redox cycling xenobiotics reduce molecular oxygen by one electron to generate superoxide. Superoxide can cause toxicities against which superoxide dismutase is protective. However, in the presence of transition metals such as iron, superoxide can generate the very reactive hydroxyl radical by the iron-catalyzed Haber-Weiss reaction. Iron is therefore normally tightly controlled by transport and storage proteins. Chemicals that can release iron from these proteins can be very toxic, causing lipid, protein, and nucleic acid oxidation. The oxidation of these species, such as a low-density lipoprotein, is generally protected by a complex antioxidant system involving glutathione and glutathione peroxidase, vitamin E, ascorbic acid, etc.

Animals↗
PubMed1993

Ferritin and ceruloplasmin in oxidative damage: review and recent findings.

The oxidation of biomolecules such as lipid, protein, and DNA is associated with a variety of toxicities and pathologies. In an all-encompassing definition these oxidative processes have been referred to as "oxidative stress." Although the direct reaction between molecular oxygen and most biomolecules is spin forbidden, this reaction can be efficiently catalyzed by transition metals such as iron and copper. Iron especially has been demonstrated to be a potent catalyst of biological oxidations. This review focuses on the relationship between iron and copper with respect to the copper protein ceruloplasmin, which may play a role in iron homeostasis by catalyzing the oxidation of iron as it is placed in ferritin.

Animals↗
PubMed1992

Production of hydroxyl radical by lignin peroxidase from Phanerochaete chrysosporium.

The mechanism for the production of hydroxyl radical by lignin peroxidase from the white rot fungus Phanerochaete chrysosporium was investigated. Ferric iron reduction was demonstrated in reaction mixtures containing lignin peroxidase isozyme H2 (LiPH2), H2O2, veratryl alcohol, oxalate, ferric chloride, and 1,10-phenanthroline. The rate of iron reduction was dependent on the concentration of oxalate and was inhibited by the addition of superoxide dismutase. The addition of ferric iron inhibited oxygen consumption in reaction mixtures containing LiPH2, H2O2, veratryl alcohol, and oxalate. Thus, the reduction of ferric iron was thought to be dependent on the LiPH2-catalyzed production of superoxide in which veratryl alcohol and oxalate serve as electron mediators. Oxalate production and degradation in nutrient nitrogen-limited cultures of P. chrysosporium was also studied. The concentration of oxalate in these cultures decreased during the period in which maximum lignin peroxidase activity (veratryl alcohol oxidation) was detected. Electron spin resonance studies using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide were used to obtain evidence for the production of the hydroxyl radical in reaction mixtures containing LiPH2, H2O2, veratryl alcohol, EDTA, and ferric chloride. It was concluded that the white rot fungus might produce hydroxyl radical via a mechanism that includes the secondary metabolites veratryl alcohol and oxalate. Such a mechanism may contribute to the ability of this fungus to degrade environmental pollutants.

Agaricales↗
PubMed1992

On the mechanism of inhibition of the veratryl alcohol oxidase activity of lignin peroxidase H2 by EDTA.

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.

Alcohol Oxidoreductases↗
PubMed1992

Rat ceruloplasmin: resistance to proteolysis and kinetic comparison with human ceruloplasmin.

Rat ceruloplasmin was purified from serum using fast protein liquid chromatography and compared to human ceruloplasmin isolated in the same manner. Rat ceruloplasmin was found to be more resistant to plasmin-mediated proteolysis than was human ceruloplasmin. Although both proteins were cleaved initially to products with apparent molecular weights of 116,000 and 20,000 Da, rat ceruloplasmin was resistant to further proteolysis, whereas the human enzyme was cleaved to smaller fragments. Primary structure differences could account for the different relative stabilities between the two enzymes. Kinetic analysis of rat ceruloplasmin produced a biphasic v vs v/s plot with apparent Km's of 40 and 1.5 microM for iron. When compared with the human enzyme, rat ceruloplasmin showed about one-fourth the ferroxidase activity and had a much broader pH profile than that of human ceruloplasmin. Rates of p-phenylenediamine oxidation by rat ceruloplasmin were about one-half those obtained with human ceruloplasmin, with maximal p-phenylenediamine oxidase activity at pH 5.0 for both enzymes.

Amino Acid Sequence↗
PubMed1992

Redox cycling of iron and lipid peroxidation.

Mechanisms of iron-catalyzed lipid peroxidation depend on the presence or absence of preformed lipid hydroperoxides (LOOH). Preformed LOOH are decomposed by Fe(II) to highly reactive lipid alkoxyl radicals, which in turn promote the formation of new LOOH. However, in the absence of LOOH, both Fe2+ and Fe3+ must be available to initiate lipid peroxidation, with optimum activity occurring as the Fe2+/Fe3+ ratio approaches unity. The simultaneous availability of Fe2+ and Fe3+ can be achieved by oxidizing some Fe2+ with hydrogen peroxide or with chelators that favor autoxidation of Fe2+ by molecular oxygen. Alternatively, one can use Fe3+ and reductants like superoxide, ascorbate or thiols. In either case excess Fe2+ oxidation or Fe3+ reduction will inhibit lipid peroxidation by converting all the iron to the Fe3+ or Fe2+ form, respectively. Superoxide dismutase and catalase can affect lipid peroxidation by affecting iron reduction/oxidation and the formation of a (1:1) Fe2+/Fe3+ ratio. Hydroxyl radical scavengers can also increase or decrease lipid peroxidation by affecting the redox cycling of iron.

Animals↗