Stability of crude ligninases: Effect of different hydrogen peroxide concentrations in the presence of aromatic alcohols

Summary In absence of veratryl alcohol (VA), Phanerochaete chrysosporium ligninases were extensively inactivated by H₂O₂ concentrations as low as 5.0 M (1 hr exposure time, pH 4.5, 38°C). In the presence of 2.5 mM VA (but not 2.5 mM benzyl alcohol), protection occurred below 500 M H₂O₂.     

Effect of hydrogen peroxide in low and superlow concentrations on DNA structure

Hydrogen peroxide in low concentrations have effect on DNA structural characteristics both in solution at 38 degrees C and in vivo, in mice organs.     

Oxidative deamination by hydrogen peroxide in the presence of metals

Various amines, including lysine residue of bovine serum albumin, were oxidatively deaminated to form the corresponding aldehydes by a H 2 O 2 /Cu 2+ oxidation system at physiological pH and temperature. The resulting aldehydes were measured by high-performance liquid chromatography. We investigated the effects of metal ions, pH, inhibitors, and O 2 on the oxidative deamination of benzylamine by H 2 O 2 . The formation of benzaldehyde was the greatest with Cu 2+ , and catalysis occurred with Co 2+ , VO 2+ , and Fe 3+ . The reaction was greatly accelerated as the pH value rose and was markedly inhibited by EDTA and catalase. Dimethyl sulfoxide and thiourea, which are hydroxyl radical scavengers, were also effective in inhibiting the generation of benzaldehyde, indicating that the reaction is a hydroxyl radical-mediated reaction. Superoxide dismutase greatly stimulated the reaction, probably due to the formation of hydroxyl radicals. O 2 was not required in the oxidation, and instead slightly inhibited the reaction. We also examined several oxidation systems. Ascorbic acid/O 2 /Cu 2+ and hemoglobin/H 2 O 2 systems also converted benzylamine to benzaldehyde. The proposed mechanism of the oxidative deamination by H 2 O 2 /Cu 2+ system is discussed.     

Accelerated CuZn-SOD-mediated oxidation and reduction in the presence of hydrogen peroxide

Copper, zinc-superoxide dismutase (CuZn-SOD) is a cytosolic, antioxidant enzyme that scavenges potentially damaging superoxide radical (()O(2)(-)). Under the proper conditions, CuZn-SOD also catalyzes the oxidation and reduction of certain small molecules. Here, we demonstrate that increased exposure to hydrogen peroxide (H(2)O(2)), a by-product of the ()O(2)(-) scavenging reaction, dramatically increases the ability of CuZn-SOD to oxidize melatonin and reduce S-nitrosoglutathione (GSNO). After a 15min in vitro incubation with CuZn-SOD and 1mM H(2)O(2), 76% of the melatonin was oxidized, compared to 52% with 0.25mM H(2)O(2), and just 9% without H(2)O(2). Pre-incubation with 1mM H(2)O(2) resulted in a 100% increase in the rate of GSNO breakdown by CuZn-SOD in the presence of glutathione (GSH) compared to untreated CuZn-SOD. Collectively, these data suggest that even small increases in intracellular H(2)O(2) levels may result in the oxidation and/or reduction of small molecules critical for proper cellular function.     

Microbial adaptation to hydrogen peroxide and biodegradation of aromatic hydrocarbons

This research investigated microbial responses to bioremediation with hydrogen peroxide (H₂O₂) as a supplemental oxygen source. Columns containing aquifer material from Traverse City, MI, USA, were continuously supplied with benzene, toluene, ethylbenzene, o-xylene and m-xylene (BTEX) and H₂O₂ in increasing concentration. The microbial responses studied were changes in microbial numbers, community structure, degradative ability, and activity of catalase and superoxide dismutase (SOD). Both adaptation to H₂O₂ and stress-related consequences were observed. Adaptation to H₂O₂ was demonstrated by increased catalase and SOD activity during the course of the experiment. The microbial community in the untreated aquifer material used in the columns consisted primarily of Corynebacterium sp and Pseudomonas fluorescens. Following amendment with 500 mg L⁻¹ H₂O₂, the column inlet was dominated by P. fluorescens with few Corynebacterium sp present; Xanthomonas maltophilia dominated the middle and outlet sections. Dimethyl phenols detected in the effluent of two of the biologically active columns were probably metabolic products. The ratio of oxygen to BTEX mass consumed was approximately 0.3 before H₂O₂ addition, 0.7 following 10 mg L⁻¹ H₂O₂ supplementation, and 2.6 over the course of the experiment. Abiotic decomposition H₂O₂ was observed in a sterile column and impeded flow at a feed concentration of 500 mg L⁻¹ H₂O₂. Increasing the BTEX concentration supplied to the biologically active columns eliminated flow disruptions by satisfying the carbon and energy demand of the oxygen evolved by increasing catalase activity. Received 15 February 1996/ Accepted in revised form 15 July 1996     

Peroxynitrite decay in the presence of hydrogen peroxide,mannitol and ethanol: A reappraisal

We have reported previously that the apparent rate of peroxynitrite (ONOO^-) decay, as followed from its absorbance at 302 nm, decreases in the presence of hydrogen peroxide, mannitol and ethanol (Alvarez et al., 1995, Chem. Res. Toxicol. 8:859-864; Alvarez et al., 1998, Free Radic. Biol. Med. 24:1331–1337). Recently, two papers confirmed the observation and proposed that this slowing effect was due to the formation of absorbing peroxynitrate (O₂NOO^-) as intermediate (Goldstein and Czapski, 1998, J. Am. Chem. Soc. 120:3458–3463; Hodges and Ingold, 1999, J. Am. Chem. Soc. 121:10695–10701). Peroxynitrate would be formed from the reaction of peroxynitrite-derived nitrogen dioxide with superoxide. Superoxide, in turn, would arise from the one-electron oxidation of hydrogen peroxide, or from the reaction of reductive radicals derived from mannitol and ethanol with dioxygen. In agreement with this concept, we show herein that under the conditions of our previous work, the slowing effect is prevented by superoxide dismutase and, in the case of mannitol and ethanol, by reducing the dioxygen concentration of the reaction solutions. Thus, superoxide formation is necessary for the decrease in the rate of absorbance decay. In addition, by simulations using known rate constants and absorption coefficients, we show that the slowing effect can be quantitatively accounted for by the formation of peroxynitrate.     

Peroxynitrite decay in the presence of hydrogen peroxide, mannitol and ethanol: a reappraisal

We have reported previously that the apparent rate of peroxynitrite (ONOO(-) ) decay, as followed from its absorbance at 302 nm, decreases in the presence of hydrogen peroxide, mannitol and ethanol (Alvarez et al., 1995, Chem. Res. Toxicol. 8:859-864; Alvarez et al., 1998, Free Radic. Biol. Med. 24:1331-1337). Recently, two papers confirmed the observation and proposed that this slowing effect was due to the formation of absorbing peroxynitrate (O(2) NOO(-) ) as intermediate (Goldstein and Czapski, 1998, J. Am. Chem. Soc. 120:3458-3463; Hodges and Ingold, 1999, J. Am. Chem. Soc. 121:10695-10701). Peroxynitrate would be formed from the reaction of peroxynitrite-derived nitrogen dioxide with superoxide. Superoxide, in turn, would arise from the one-electron oxidation of hydrogen peroxide, or from the reaction of reductive radicals derived from mannitol and ethanol with dioxygen. In agreement with this concept, we show herein that under the conditions of our previous work, the slowing effect is prevented by superoxide dismutase and, in the case of mannitol and ethanol, by reducing the dioxygen concentration of the reaction solutions. Thus, superoxide formation is necessary for the decrease in the rate of absorbance decay. In addition, by simulations using known rate constants and absorption coefficients, we show that the slowing effect can be quantitatively accounted for by the formation of peroxynitrate.     

N-dealkylation of aminopyrine catalyzed by soybean lipoxygenase in the presence of hydrogen peroxide

A hypothesis that lipoxygenase may mediate N-dealkylation of xenobiotics was investigated using the prototype drug aminopyrine and soybean lipoxygenase as a model enzyme in the presence of hydrogen peroxide. Formaldehyde production as a result of N-demethylation of aminopyrine exhibited pH optimum of 6.5. The reaction was dependent on the incubation time, amount of enzyme, and concentration of aminopyrine and hydrogen peroxide. Under the experimental conditions employed, the specific activity for N-demethylation of aminopyrine was found to be 823 ± 93 nmoles per min/mg protein or 89 ± 10 nmoles per min/nmole of enzyme. The reaction was significantly inhibited by nordihydroguaiaretic acid and gossypol, the classical inhibitors of lipoxygenase. Spectrophotometric analyses indicated the generation of a nitrogen-centered free-radical cation as the initial oxidation product of aminopyrine. The rate of accumulation of this radical species was also dependent on pH, the amount of enzyme, and concentration of aminopyrine and hydrogen peroxide. The radical production was markedly suppressed by ascorbate, glutathione, and dithiothreitol in a concentration-dependent manner. Preliminary data gathered for the oxidation of other chemicals indicated that the lipoxygenase exhibits a unique substrate specificity. Collectively, the evidence presented suggests for the first time that lipoxygenase pathway may be involved in N-demethylation of aminopyrine and other chemicals. © 1998 John Wiley & Sons, Inc. J Biochem Toxicol 12: 175–183, 1998     

Degradation of high-molecular-weight hyaluronan by hydrogen peroxide in the presence of cupric ions

Dynamic viscosity (eta) of the high-molecular-weight hyaluronan (HA) solution was measured by a Brookfield rotational viscometer equipped with a Teflon cup and spindle of coaxial cylindrical geometry. The decrease of eta of the HA solution, indicating degradation of the biopolymer, was induced by a system containing H2O2 alone or H2O2 plus CuCl2. The reaction system H2O2 plus CuCl2 as investigated by EPR spin-trapping technique revealed the formation of a four-line EPR signal characteristic of a *DMPO-OH spin adduct. Thus, hydroxyl radicals are implicated in degradation of high-molecular-weight HA by the system containing H2O2 and CuCl2.     

Pretreatment of lignocellulosic materials with hydrogen peroxide in presence of manganese compounds

Pretreatment of lignocellulosic materials such as newspaper, rice straw, pulp waste, and municipal solid waste with hydrogen peroxide in the presence of manganese compounds greatly enhances their susceptibility to enzymatic saccharification. This pretreatment can be achieved using rather mild conditions with only a minimal decrease in the recovery and little change in composition. Manganese salts in this hydrogen peroxide pretreatment works effectively in particular when the concentration of hydrogen peroxide is relatively low. The susceptibility of hydrogen-peroxide-pretreated substrate to enzymatic saccharification increases with increasing the molar ratio of manganes to hydrogen peroxide up to 1 : 100.     

Effect of temperature on glucagon secretion in the presence of different concentrations of glucose]

Lowering the temperature from 37.5 degrees C to 28 degrees C does not alter the glucagon secretion by the isolated perfused rat pancreas in response to different glucose concentrations (0 g/l 1.5 g/l, 3 g/l and 5 g/l).     

A mechanism of luminol-dependent chemiluminescence of human serum in the presence of hydrogen peroxide

Comparative role of proteins of the human blood plasma in luminol-dependent induction of chemiluminescence in the presence of hydrogen peroxide was studied. It was found that the largest contribution into chemiluminescence was made by the plasma fraction with the molecular mass 250 kD. Besides the intensity of chemiluminescence proves to be proportional to hemoglobin concentration, which when added to the blood plasma entered the fractions with the molecular mass about 250 kD. It is suggested that hemoglobin producing luminescence in the blood plasma is related to haptoglobin.     

Fluorimetric study of the pro-oxidant activity of EUK8 in the presence of hydrogen peroxide

The catalase mimetic complex Mn(III)-salen chloride (EUK8) was found to be pro-oxidant under low hydrogen peroxide concentrations. The increase in the fluorescence rate of the probe 1,2,3-dihydrorhodamine (DHR) in solution, as well as the carbonyl content of human serum albumin were found to be maximum at H2O2:EUK8 molar ratios ranging from 0 to 2, supporting previous findings regarding the mechanism of EUK8 catalase activity and the formation of highly oxidative Mn(V)-O2- species. This pro-oxidant effect is precluded by the presence of glutathione. Cytotoxicity to HeLa cells, as probed by increased rate of oxidation of intracellular DHR, was not observed. Our findings suggest that the combination of H2O2 and EUK8 at specific molar ratios, in the absence of reductants/antioxidants, induces the oxidation of organic molecules. It is shown that the fluorimetric determination of pro-oxidant activity of metal complexes is more sensitive than the colorimetric quantification of protein carbonyl content. The implications of our findings with respect to the somewhat confusing results arising from in vivo studies of EUK8 and other Mn(III) anti-oxidant metal complexes are discussed.