Showing papers on "Hydrogen peroxide published in 1978"

The biology of oxygen radicals

Abstract: The reactive superoxide radical, O2-, formerly of concern only to radiation chemists and radiobiologists, is now understood to be a normal product of the biological reduction of molecular oxygen. An unusual family of enzymes, the superoxide dismutases, protect against the deleterious actions of this radical by catalyzing its dismutation to hydrogen peroxide plus oxygen.

Do Mitochondria Produce Oxygen Radicals in vivo

Abstract: 1 Heart mitochondria from rats at 3 months and 23 months of age were investigated for their capacity to generate oxygen radicals and hydrogen peroxide. 2 Highest values for O2+-formation were obtained with submitochondrial particles freed from superoxide dismutase after the addition of succinate and antimycin A to start the reaction. Under these conditions superoxide-radical formation with mitochondria from old rats (2.54 nmol × min−1× mg−1) exceeded formation rates in the young controls (1.9 nmol × min−1× mg−1) by 25%. 3 A constant fraction of 20% of the radicals produced escaped quenching by intramitochondrial superoxide dismutase. This fraction was independent of the rate of radical formation; its magnitude was deduced from generation rates of hydrogen peroxide in the presence and absence of exogenous superoxide dismutase. 4 Free oxygen radicals could be obtained with intact rat-heart mitochondria as well following the addition of ATP, a system which is closer to physiological states. Formation rates of oxygen radicals observed under these conditions were similar to those seen in the particulate fractions which escaped quenching by mitochondrial superoxide dismutase. 5 Peroxidative degradation of membrane lipids was found to parallel steady-state concentrations of free oxygen radicals. 6 The results are discusssed in terms of a radical-generating mechanism which functions in vivo at the level of the mitochondrial electron-transferring system.

Multilayer film elements for clinical analysis: applications to representative chemical determinations.

Abstract: Using the general concept of a dry multilayer analytical element, we can change chemical procedures and configurations to assay several blood components. In the assay of serum urea nitrogen, urease in the reagent layer catalyzes the hydrolysis of urea. A semipermeable membrane excludes aqueous base, but allows ammonia to diffuse to an underlying indicator layer. For the amylase determination, the enzyme hydrolyzes a dyed-starch substrate coated on top of the spreading layer; this produces small fragments, which diffuse to a registration layer. The increase of absorbance at 540 nm is correlated with amylase activity. Bilirubin complexes with a cationic polymer at the interface between the spreading and reagent layers. The direct reading at 460 nm allows determination of total bilirubin in the range 1 to 500 mg/liter. Tirglycerides are hydrolyzed in the spreading layer, and the resulting soluble glycerol readily diffuses into the reagent layer, where it is phosphorylated and subsequently oxidized by glycerophosphate oxidase to yield dihydroxyacetone phosphate and hydrogen peroxide. Peroxidase catalyzes production of a color commensurate with the hydrogen peroxide produced.

Lignin synthesis: The generation of hydrogen peroxide and superoxide by horseradish peroxidase and its stimulation by manganese (II) and phenols.

Abstract: The enzyme horseradish peroxidase (EC 1.11.1.7) catalyses oxidation of NADH. NADH oxidation is prevented by addition of the enzyme superoxide dismutase (EC 1.15.1.1) to the reaction mixture before adding peroxidase but addition of dismutase after peroxidase has little inhibitory effect. Catalase (EC 1.11.1.6) inhibits peroxidase-catalysed NADH oxidation when added at any time during the reaction. Apparently the peroxidase uses hydrogen peroxide (H2O2) generated by non-enzymic breakdown of NADH to catalyse oxidation of NADH to a free-radical, NAD., which reduces oxygen to the superoxide free-radical ion, O2 .-. Some of the O2 .- reacts with peroxidase to give peroxidase compound III, which is catalytically inactive in NADH oxidation. The remaining O2 .- undergoes dismutation to O2 and H2O2. O2 .- does not react with NADH at significant rates. Mn2+ or lactate dehydrogenase stimulate NADH oxidation by peroxidase because they mediate a reaction between O2 .- and NADH. 2,4-Dichlorophenol, p-cresol and 4-hydroxycinnamic acid stimulate NADH oxidation by peroxidase, probably by breaking down compound III and so increasing the amount of active peroxidase in the reaction mixture. Oxidation in the presence of these phenols is greatly increased by adding H2O2. The rate of NADH oxidation by peroxidase is greatest in the presence of both Mn2+ and those phenols which interact with compound III. Both O2 .- and H2O2 are involved in this oxidation, which plays an important role in lignin synthesis.

Differences in Oxygen Metabolism of Phagocytosing Monocytes and Neutrophils

Abstract: The oxidative metabolism of monocytes and polymorphonuclear leukocytes from human peripheral blood was studied in resting and phagocytosing cells. Monocytes, like neutrophils, showed an increase in oxygen consumption during phagocytosis with a concurrent release of superoxide anions and hydrogen peroxide. Both oxygen products are highly reactive agents with potential bactericidal activity. Neutrophils consumed two and a half times as much oxygen, generated about twice as much superoxide, and released five times as much hydrogen peroxide as monocytes did. Monocytes generated superoxide and hydrogen peroxide at equivalent rates. Antimycin A, a specific mitochondrial respiratory chain inhibitor, depressed the oxygen consumption of monocytes by 70% but had no effect on neutrophil respiration. Therefore, the oxygen consumed by phagocytosing monocytes appeared to be metabolized in two distinct processes: 30% of the oxygen is converted to hydrogen peroxide, whereas the remaining 70% is metabolized via the mitochondrial respiratory chain. The release of superoxide and hydrogen peroxide was unaffected by antimycin in either cell type. Phagocytosis of zymosan particles by monocytes was nearly abolished by antimycin, whereas no effect was noted with neutrophils. Thus, phagocytosis appears to be highly dependent on oxidative phosphorylation in monocytes but not in polymorphonuclear leukocytes. Moreover, in monocytes treated with antimycin, an addition of opsonized zymosan particles induced stimulation of the oxidative metabolism without occurrence of ingestion.

The haber-weiss cycle

Abstract: — The Haber-Weiss cycle: was investigated at low pH by radiolysis of oxygen or nitrogen saturated solutions of hydrogen peroxide. It was found that reaction 2 has a low rate constant: k2= 3.0 ± 0.6 M-1 s-1 (pH 2.3, 22°C). The rate determining step of reaction 2 is most probably the transfer of an electron from a π8* orbital of HO2 to the empty su* orbital of H2O2. Overlap between these two orbitals is hindered by the filled π8* orbitals of H2O2. Fe(HI)EDTA catalyses reaction 2.

Human granulocyte generation of hydroxyl radical.

Abstract: Human granulocytes were capable of oxidizing 2-keto-4 thiomethylbutyric acid to ethylene during phagocytosis or membrane perturbation. The reaction required hydrogen peroxide and superoxide and in addition was inhibited by various hydroxyl radical (OH) scavengers. These observations represent direct evidence for the generation of OH by human granulocytes. Further, inhibition of ethylene generation by azide and cyanide suggests that OH generation in granulocytes may be linked to myeloperoxidase.

Hydrogen peroxide in hepatic microsomes.

Abstract: Publisher Summary This chapter talks about the hydrogen peroxide in hepatic microsomes. H 2 O 2 determination in microsomes is dependent on a method that fulfills some requirements. Those requirements are (1) it is sensitive enough to permit determination of 1 μM H 2 O 2 without interfering with monooxygenase-dependent hydroxylation reactions, (2) allows to eliminate the influence of various substrates or products of mixed-function oxidation reactions, (3) permits inhibition of contaminating catalase so that during an incubation period measurements not only of small steady-state concentrations, but also of rate and extent of H 2 O 2 formation are possible, and (4) allows to determine possible degradation of H 2 O 2 by residual catalase-, peroxidase-, or NADPH-dependent mixed-function oxygenase activity. The reason that in the presence of sodium azide H 2 O 2 accumulates and is subjected to further metabolism by pathways other than catalase, for example NADPH-dependent mixed-function oxygenase, the trapping of H 2 O 2 as HCHO by the addition of exogenous catalase and methanol avoids such degradation. Under circumstances where H 2 O 2 accumulates, the measurements of rate and extent of H 2 O 2 formation in microsomes can vary depending on the method applied.

Activated oxygen species and oxidation of food constituents

Abstract: Activated oxygen species which may be important in initiating oxidative changes in foods include singlet oxygen, hydroxyl radical, ozone, superoxide anion (perhydroxyl radical at low pH), and hydrogen peroxide. Chemical and enzymic reactions known to occur in biological materials can generate singlet oxygen, hydroxyl radical, superoxide anion, and hydrogen peroxide. Ozone is primarily a product of photoreactions in polluted air. Reactions involving singlet oxygen, hydroxyl radical, and ozone with food constituents can ultimately yield peroxides which decompose to initiate oxidative chain reactions. Superoxide anion and hydrogen peroxide are relatively inert toward organic molecules but can decompose to produce the more reactive singlet oxygen and hydroxyl radical. Inhibition of reactions initiated by reactive oxygen species in foods should be very important in preserving the oxidative stability of foods. The generation, detection, measurement, reaction, and inhibition of reactions of active oxygen species are surveyed in this review.

Identification of hydrogen peroxide as a photoproduct toxic to human cells in tissue-culture medium irradiated with "daylight" fluorescent light

Abstract: Hydrogen peroxide, lethal for human cells, is produced in Dulbecco's modified Eagle's tissue culture medium when exposed to “daylight” fluorescent light. Addition of pure H2O2 and use of the enzyme catalase demonstrate that about 40% of the toxicity in irradiated medium is due to generated peroxide. Riboflavin and tryptophan, or riboflavin and tyrosine, are the components necessary for formation of lethal levels of H2O2 during light exposure.

Hydrogen peroxide production, chemiluminescence, and the respiratory burst of fertilization: Interrelated events in early sea urchin development

Abstract: After fertilization of the sea urchin, Strongyl-ocentrotus purpuratus, a crosslinked fertilization membrane is formed; the crosslinks (dityrosine residues) are synthesized in a reaction catalyzed by an ovoperoxidase that is released from the cortical granules during fertilization. The substrate for ovoperoxidase activity, hydrogen peroxide, is generated by the egg coincident with the “respiratory burst” that follows parthenogenetic activation by the divalent ionophore A23187 or fertilization. This burst of oxygen consumption may be almost quantitatively accounted for by hydrogen peroxide evolution, as measured by the peroxidase-catalyzed quenching of scopoletin fluorescence. Neither the burst of oxygen consumption nor hydrogen peroxide production occurs when the inhibitor of cortical granule discharge, procaine, is present at fertilization. Fertilization or parthenogenetic activation with A23187 also is associated with a burst of light emission. This chemiluminescence is inhibited in vivo by inhibitors of the ovoperoxidase, such as 3-amino-1,2,4-triazole, phenylhydrazine, sulfite, or azide. A crude ovoperoxidase preparation catalyzes hydrogen peroxide-dependent chemiluminescence that is similarly inhibited. Thus, the bursts of oxygen uptake, peroxide production, and chemiluminescence appear to be several manifestations of the peroxidative system released at fertilization. This system may additionally be responsible for spermicidal activity and thus may act as a component of the block to polyspermy.

Hydrogen peroxide and superoxide radical formation in anaerobic broth media exposed to atmospheric oxygen.

Abstract: Fourteen different broth media were autoclaved under anaerobic conditions and then exposed to atmospheric oxygen. The hydrogen peroxide and superoxide radical formation as well as the bactericidal effect of the media were studied. The rate of killing of Peptostreptococcus anaerobius VPI 4330-1 was high in media that rapidly autoxidized and accumulated hydrogen peroxide. In actinomyces broth (BBL), 50% of the cells were killed within 2 min, and in Brewer thioglycolate medium (Difco), 50% were killed within 11 min, whereas more than 50% of the cells survived for more than 2 h in Clausen medium (Oxoid), fluid thioglycolate medium (BBL), and thioglycolate medium without dextrose or indicator (Difco). Only media that contained phosphate and glucose had a tendency to accumulate hydrogen peroxide. A solution of phosphate and glucose autoxidized when it had been heated to 120 degrees C for at least 5 min and when the pH of the solution was higher than 6.5. Transitional metal ions catalyzed the autoxidation, but they were not necessary for the reaction to occur. Of the other substances heated in phosphate buffer, only alpha-hydroxycarbonyl compounds autoxidized with accumulation of hydrogen peroxide. Superoxide dismutase decreased the autoxidation rate of most of the broth media. This indicated that superoxide radicals were generated in these media.

Fatty acid beta-oxidation system in microbodies of n-alkane-grown Candida tropicalis.

Abstract: Localization of fatty acid beta-oxidation system in microbodies of Candida tropicalis cells growing on n-alkanes was studied. Microbodies isolated from the yeast cells showed palmitate-dependent activities of NAD reduction, acetyl-CoA formation and oxygen consumption. When sodium azide, an inhibitor of catalase, was added to the system, palmitate-dependent formation of hydrogen peroxide was observed. Stoichiometric study revealed that two moles of NAD were reduced per one mole of oxygen consumed in the absence of sodium azide and the presence of the inhibitor doubled the oxygen consumption by microbodies without an appreciable change in NAD reduction. These results indicate that the yeast microbodies contain beta-oxidation system of fatty acid, and that catalase located in the organelles participates in the degradation of hydrogen peroxide to be formed at the step of dehydrogenation of acyl-CoA.

Cytotoxic reactions of free radical species of oxygen.

Abstract: — We report on autooxidation reactions related to selective cell killing in vivo and present oxygen uptake and EPR data on the molecular nature of these changes, with a note on a reaction used to test for singlet oxygen. Selective obliteration by 6-hydroxydopamine, 6-aminodopamine and their congeners of beta-adrenergic cell receptors and of adrenergic and dopaminergic neurons in vivo and in vitro have been reported recently. These effects devolve from autoxidation of the compounds in situ after appropriate biological concentration, but it is unclear whether cytotoxicity is mediated by the reactive oxygen species themselves or by nucleophilic reactions of the product quinones. Because of the possibility of harnessing these reactions for a generalized “chemical surgery” if the former mechanism is operative, and because many other oxidative damage reactions involving unsaturated lipids of biomembranes seem to share similar autoxidative initiating and chain-carrying steps, we have studied the autoxidation of ascorbate and other reductants catalyzed by polyhydroxy quinols related to 6-hydroxydopamine. We find that superoxide anion mediation may or may not be important, depending on redox potentials and reaction kinetics of particular compounds. To the extent that the cellular toxicity of these compounds is oxidative in nature, it is facilitated by—and may depend upon—hydroxyl radical production due to Fenton-type reactions. Likely Fenton reactants in vivo are hydrogen peroxide produced from the quinol-catalyzed autoxidations and non-heme iron reduced cyclically by superoxide anions from the same autoxidations. Studies using flow systems adapted for EPR at 35 GHz have provided support for some of the reaction mechanisms proposed. In nonaqueous solvents eerie oxidation produced transient free radicals from hydrophobic diphenyl and isobenzo furans, which are often cited as “specific” probes for singlet oxygen detection in biochemistry.

The generation of hydroxyl radicals in biologic systems: toxicological aspects.

Abstract: — The formation of hydroxyl radicals in vitro was studied through their reaction with 2-keto-4-thiomethylbutyric acid to form ethylene gas. The autoxidation reaction of 6-aminodopamine served as a model source of hydroxyl radicals. Ethylene production was suppressed by catalase and by superoxide dismutase, indicating that both hydrogen peroxide and superoxide were involved in the reaction. Hydroxyl radical scavengers (thiourea > benzoate > ethanol) suppressed ethylene production in good agreement with their respective rate constants for reaction with hydroxyl radicals. Urea served as a negative control. Several substituted thiourea derivatives also suppressed ethylene production to a similar degree as thiourea itself. Biologic studies centered on several cytotoxic agents whose mechanisms of action are thought to involve hydroxyl radicals. These agents included alloxan, which destroys the beta cells of the pancreas, and 6-hydroxy- and 6-aminodopamine, which destroy sympathetic nerves. Damage to tissues in vivo was blocked to varying degrees by pretreatment of animals with hydroxyl radical scavengers such as ethanol or the thiourea derivatives. In addition, hydroxyl radical scavengers blocked the action of 5,7-dihydroxytryptamine, a neurotoxin whose effects on noradrenaline neurons were previously shown to be blocked by inhibitors of monoamine oxidase. The data indicate that these cell toxins produce their damaging actions on specific target cells through the intracellular generation of hydroxyl radicals.

Ultraviolet absorption cross sections of hydrogen peroxide

Abstract: Absorption cross-sections of hydrogen peroxide vapor and of neutral aqueous solutions of hydrogen peroxide were measured in the wavelength range from 195 to 350 nm at 296 K. The spectrophotometric procedure is described, and the reported cross-sections are compared with values obtained by other researchers. Photodissociation coefficients of atmospheric H2O2 were calculated for direct absorption of unscattered solar radiation, and the vertical distributions of these coefficients are shown for various solar zenith angles.