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At least 307 records · Page 17Linked to original sources
PubMed2003

Tryptophan-14 is the preferred site of DBNBS spin trapping in the self-peroxidation reaction of sperm whale metmyoglobin with a single equivalent of hydrogen peroxide.

The 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS)-metmyoglobin adduct formed following the horse metmyoglobin-H(2)O(2) reaction has been assigned to both a tyrosyl and a tryptophanyl residue radical. At low H(2)O(2), hyperfine coupling to a (13)C atom in sperm whale metmyoglobin labeled at the tryptophan residues with (13)C allowed the unequivocal assignment of the primary adduct to a tryptophanyl radical. Trapping at Trp-14 of sperm whale myoglobin was indicated by greatly decreased electron paramagnetic resonance (EPR) spectral intensity of the DBNBS adducts of the Trp-14-Phe recombinant proteins. Complex EPR spectra with partially resolved hyperfine splittings from several atoms were obtained by pronase treatment of the DBNBS/*W14F metmyoglobin adducts. The EPR spectra of authentic DBNBS/*Tyr adducts were incubation time-dependent; the late time spectra resembled the spectra of pronase-treated DBNBS/*W14F sperm whale myoglobin adducts, suggesting formation of an unstable tyrosyl radical adduct in the latter proteins. When the H(2)O(2):metmyoglobin ratio was increased to 5:1, the EPR spectrum after pronase treatment supported trapping of a tyrosyl radical, although similar decreases in tryptophan content were detected at H(2)O(2):metmyoglobin ratios of 1:1 and 5:1.

Animals↗
PubMed1975

Optical measurement of the catalase-hydrogen peroxide intermediate (Compound I) in the liver of anaesthetized rats and its implication to hydrogen peroxide production in situ.

The spectrophotometric determination of the catalase-H2O2 intermediate (Compound I) was extended to the liver in situ in anaesthetized rats. The rate of H2O2 production was determined for the liver in situ with endogenous substrates, and in the presence of excess of glycollate. Glycollate infusion doubled H2O2 production rate in the liver of air-breathing rats, and caused a fourfold increase when rats breathed O2 at 1 times 10(5) Pa. Hyperbaric O2 up to 6 times 10(5) Pa did not increase H2O2 generation supported by endogenous substrates, nor did it increase H2O2 production above that produced by 1 times 10(5) Pa O2 in glycollate-supplemented rats. The rates of ethanol oxidation via hepatic catalase and via alcohol dehydrogenase in the whole body were separately measured. The contribution of hepatic catalase to ethanol oxidation was found to be approx. 10 percent in endogenous conditions and increased to 30 percent or more of the total ethanol oxidation in rats supplemented with glycolate.

Alcohol Oxidoreductases↗
PubMed1978

The role of peroxide in haem degradation. A study of the oxidation of ferrihaems by hydrogen peroxide.

The oxidation of ferrihaems by H2O2 was studied as a model for haem catabolism. Rates of ferrihaem oxidation were evaluated by using a new computer-based method that measures the loss in catalytic activity of the ferrihaem during oxidation. For protoferrihaem, deuteroferrihaem, coproferrihaem and mesoferrihaem, oxidation proceeded via the monomeric species and no dimer contribution was detectable. The pH-dependence of oxidation was studied in the range 6.5--11. Within experimental error, the data were compatible with an inverse linear dependence on [H+]. This was interpreted in terms of attack by HO2- on monomeric ferrihaem. The specific second-order rate constants for oxidation of monomeric species by HO2- were of the same order of magnitude for all the ferrihaems, and were in the sequence coproferrihaem greater than protoferrihaem greater than mesoferrihaem congruent to deuteroferrihaem. A model is suggested involving formation of a ferrihaem monomerperoxide complex, which may either dissociate with the formation of a peroxidatic intermediate or be involved in an intramolecular oxidation of the ferrihaem. Haem catabolism may occur via the same or a similar intermediate.

Coproporphyrins↗
PubMed2004

Carbon dioxide mediates Mn(II)-catalyzed decomposition of hydrogen peroxide and peroxidation reactions.

Mn(II) can catalyze the decomposition of H(2)O(2) and, in the presence of H(2)O(2), can catalyze the oxidation of NADH. Strikingly, these processes depend on the simultaneous presence of both CO(2) and HCO(3)(-). This explains the exponential dependence of the rates on [HCO(3)(-)], previously noted by other workers. These processes are inhibited by Mn-superoxide dismutase, establishing the generation of O(2)(-) and its role as an essential reactant. A scheme of reactions, consistent with the known properties of this system, is proposed. The large rate enhancements provided by HCO(3)(-) + CO(2), and the abundance of both of these species in vivo, suggest that similar reactions have relevance to the oxidative stress imposed by O(2)(-) and H(2)O(2).

Carbon Dioxide↗
PubMed1990

Manganese(II) catalyzes the bicarbonate-dependent oxidation of amino acids by hydrogen peroxide and the amino acid-facilitated dismutation of hydrogen peroxide.

In bicarbonate/CO2 buffer, Mn(II) and Fe(II) catalyze the oxidation of amino acids by H2O2 and the dismutation of H2O2. As the Mn(II)/Fe(II) ratio is increased, the yield of carbonyl compounds per mole of leucine oxidized is essentially constant, but the ratio of alpha-ketoisocaproate to isovaleraldehyde formed increases, and the fraction of H2O2 converted to O2 increases. In the absence of Fe(II), the rate of Mn(II)-catalyzed leucine oxidation is directly proportional to the H2O2, Mn(II), and amino acid concentrations and is proportional to the square of the HCO3- concentration. The rate of Mn(II)-catalyzed O2 production in the presence of 50 mM alanine or leucine is about 4-fold the rate observed in the absence of amino acids and accounts for about half of the H2O2 consumed; the other half of the H2O2 is consumed in the oxidation of the amino acids. In contrast, O2 production is increased nearly 18-fold by the presence of alpha-methylalanine and accounts for about 90% of the H2O2 consumed. The data are consistent with the view that H2O2 decomposition is an inner sphere (cage-like) process catalyzed by a Mn coordination complex of the composition Mn(II), amino acid, (HCO3-)2. Oxidation of the amino acid in this complex most likely proceeds by a free radical mechanism involving hydrogen abstraction from the alpha-carbon as a critical step. The results demonstrate that at physiological concentrations of HCO3- and CO2, Mn(II) is able to facilitate Fenton-type reactions.

Alanine↗
PubMed2006

Non-oxygen-forming pathways of hydrogen peroxide degradation by bovine liver catalase at low hydrogen peroxide fluxes.

Heme catalases are considered to degrade two molecules of H(2)O(2) to two molecules of H(2)O and one molecule of O(2) employing the catalatic cycle. We here studied the catalytic behaviour of bovine liver catalase at low fluxes of H(2)O(2) (relative to catalase concentration), adjusted by H(2)O(2)-generating systems. At a ratio of a H(2)O(2) flux (given in microM/min(- 1)) to catalase concentration (given in microM) of 10 min(- 1) and above, H(2)O(2) degradation occurred via the catalatic cycle. At lower ratios, however, H(2)O(2) degradation proceeded with increasingly diminished production of O(2). At a ratio of 1 min(- 1), O(2) formation could no longer be observed, although the enzyme still degraded H(2)O(2). These results strongly suggest that at low physiological H(2)O(2) fluxes H(2)O(2) is preferentially metabolised reductively to H(2)O, without release of O(2). The pathways involved in the reductive metabolism of H(2)O(2) are presumably those previously reported as inactivation and reactivation pathways. They start from compound I and are operative at low and high H(2)O(2) fluxes but kinetically outcompete the reaction of compound I with H(2)O(2) at low H(2)O(2) production rates. In the absence of NADPH, the reducing equivalents for the reductive metabolism of H(2)O(2) are most likely provided by the protein moiety of the enzyme. In the presence of NADPH, they are at least in part provided by the coenzyme.

Animals↗
PubMed1996

AG8 cells, which are highly resistant to hydrogen peroxide, display collateral sensitivity to the combination of hydrogen peroxide and L-histidine.

The results obtained in the present study indicate that AG8 cells, which are highly resistant to H2O2, are not cross-resistant to the combination of H2O2/L-histidine. In fact, once the influence of elevated catalase on the AG8 pheno-type has been circumvented (by treatment of AG8 cells with aminotriazole), AG8 cells display essentially no cross-resistance to the H2O2/L-histidine cocktail while retaining considerable resistance to H2O2 alone (when compared to wild-type AA8 cells). Although H2O2 alone dose not produce DNA double strand breaks (DSBs), this type of lesion was readily detected upon exposure of sensitive or resistant cells to the oxidant in the presence of the amino acid. Interestingly, similar levels of DNA DSBs were detected in AA8 and catalase-depleted AG8 cells. An excellent correlation was found when the cytotoxicity and the level of DNA DSBs obtained in sensitive and resistant cells (with normal or reduced catalase levels) challenged with the cocktail H2O2/L-histidine were compared. This would suggest that DSBs produced on a per cell basis always result in an equal level of toxicity, regardless of the cell type (resistant versus sensitive cell line), the lethality of each of these cell lines being dependent on the number of induced DSBs. In conclusion, the results presented here provide further evidence in support of the hypothesis that cell killing elicited by the combination of H2O2/L-histidine involves a mechanism distinct from that following treatment with H2O2 alone. The fact that H2O2-resistant AG8 cells, which are not cross-resistant to agents promoting cell death via DNA DSB-induction, display collateral sensitivity to the cocktail H2O2/L-histidine, strongly suggests that cell killing triggered by this treatment is mediated by DNA double strand breakage.

Animals↗
PubMed1990

Peroxidase/hydrogen peroxide--or bone marrow homogenate/hydrogen peroxide--mediated activation of phenol and binding to protein.

1. 14C-Phenol was metabolized by rat bone marrow homogenate and H2O2. The homogenate catalyst, however, was inactivated by preincubation with H2O2, presumably due to inactivation of the enzyme(s) involved in phenol metabolism. 2. The majority of the metabolized 14C-phenol was bound to bone marrow proteins. o,o'-Biphenol and p,p'-biphenol were the principal non-protein-bound products. Ascorbate was unable to remove phenol oxidation products bound to protein, although o,o'-biphenol recovery from the reaction mixture was markedly enhanced. Prior alkylation of protein thiols with N-ethylmaleimide decreased the binding of 14C-phenol oxidation products to bone marrow proteins by only 10-20%. 3. 14C-Phenol (200 microM) metabolism by horseradish peroxidase (10 micrograms) and H2O2 (200 microM) also resulted in extensive binding to externally added bovine serum albumin. The absorption spectrum of 14C-phenol oxidation products bound to bovine serum albumin was similar to that of bound oxidation products of o,o'-biphenol but not of p,p'-biphenol. 4. Protease digestion of bovine serum albumin bound 14C-phenol oxidation products, followed by ethyl acetate extraction, extracted 75% of the 14C, indicating that most of the binding is probably non-covalent. Up to 32% of the 14C-phenol oxidation products binding to bovine serum albumin may be covalent, since derivation with dinitrofluorobenzene and extraction under acid, but not alkaline, conditions extracted the 14C. The percentage of metabolites covalently bound to bovine serum albumin was increased to 59% when horseradish peroxidase concentration was decreased to 0.2 micrograms. 5. The thiol groups of bovine serum albumin were unaffected by o,o'-biphenol oxidation products, slightly decreased by phenol oxidation products, but were completely depleted by p,p'-biphenol oxidation products. 6. These results indicate that o,o'-biphenol oxidation products are responsible for much of the 14C-phenol binding to protein.

Amino Acids↗