Hydrogen peroxide

About: Hydrogen peroxide is a research topic. Over the lifetime, 42583 publications have been published within this topic receiving 1043732 citations. The topic is also known as: H2O2 & dioxidane.

Formation of hydrogen peroxide by isolated cell walls from horseradish (Armoracia lapathifolia Gilib.).

Abstract: Isolated cell-wall suspensions from horseradish in the presence of 5×10(-4) M MnCl2 catalyze the production of hydrogen peroxide at the expense of either NADPH or NADH. This reaction is inhibited by scavengers of the superoxide free radical ion such as ascorbate or dihydroxyphenols or by superoxide dismutase, and stimulated by monophenols such as p-coumaric acid. On comparison with isolated (commercial) horseradish peroxidase it becomes evident that (a) cell-wall-bound peroxidase(s) is (are) responsible for the production of hydrogenperoxide, involving the superoxide free radical ion as an intermediate of the complex reaction chain.

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.

Hypochlorite-induced damage to proteins: formation of nitrogen-centred radicals from lysine residues and their role in protein fragmentation

Abstract: Stimulated monocytes and neutrophils generate hypochlorite (HOCl) via the release of the enzyme myeloperoxidase and hydrogen peroxide. HOCl damages proteins by reaction with amino acid side-chains or backbone cleavage. Little information is available about the mechanisms and intermediates involved in these reactions. EPR spin trapping has been employed to identify radicals on proteins, peptides and amino acids after treatment with HOCl. Reaction with HOCl gives both high- and low-molecular-mass nitrogen-centred, protein-derived radicals; the yield of the latter increases with both higher HOCl:protein ratios and enzymic digestion. These radicals, which arise from lysine side-chain amino groups, react with ascorbate, glutathione and Trolox. Reaction of HOCl-treated proteins with excess methionine eliminates radical formation, which is consistent with lysine-derived chloramines (via homolysis of N-Cl bonds) being the radical source. Incubation of HOCl-treated proteins, after removal of excess oxidant, gives rise to both nitrogen-centred radicals, over a period of hours, and time-dependent fragmentation of the protein. Treatment with excess methionine or antioxidants (Trolox, ascorbate, glutathione) protects against fragmentation; urate and bilirubin do not. Chloramine formation and nitrogen-centred radicals are therefore key species in HOCl-induced protein fragmentation.

Formation of peroxides in amino acids and proteins exposed to oxygen free radicals

Abstract: Dilute aqueous solutions of BSA or lysozyme gave positive tests for peroxides after exposure to reactive oxygen species. The reactive species were generated by gamma-irradiation, reduction of H2O2 with Fe2+ ions or thermal decomposition of an azo compound. Peroxides were assayed by an iodometric method. Identification of the new groups as hydroperoxides was confirmed by their ability to oxidize a range of compounds and by the kinetics of their reaction with iodide. The hydroperoxide groups were bound to the proteins and their yields (G values) corresponded to 1.2 -OOH groups per 100 eV of radiation energy absorbed for BSA, and 0.8 for lysozyme. The oxygen free radicals effective in protein peroxidation were the hydroxyl and organic peroxyl, but not superoxide or its protonated form. The efficiency of BSA peroxidation initiated by the hydroxyl radicals was 40%. Protein peroxides decayed spontaneously with a half-life of about 1.5 days at 20 degrees C. Exposure of the common amino acids to hydroxyl free radicals showed that six of them (glutamate, isoleucine, leucine, lysine, proline and valine) were peroxidized with similar efficiency to the proteins, whereas the rest were inert or much less susceptible. These results suggest that some proteins may be peroxidized by a variety of agents in vivo and that their subsequent reactions with protective agents, such as ascorbate or glutathione, may decrease the antioxidant potential of cells and tissues.