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Query: UNIPROT:P04040 (Catalase)
 3,577 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The NADPH-supported enzymatic reduction of molecular oxygen by ferredoxin-ferredoxin:NADP+ oxidoreductase was investigated. The ESR spin trapping technique was employed to identify the free radical metabolites of oxygen. The spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used to trap and identify the oxygen-derived free radicals. [17O]Oxygen was employed to demonstrate that the oxygen-centered radicals arose from molecular oxygen. From the data, the following scheme is proposed: (Formula:see text). The formation of the free hydroxyl radical during the reduction of oxygen was demonstrated with quantitative competition experiments. The hydroxyl radical abstracted hydrogen from ethanol or formate, and the resulting scavenger-derived free radical was trapped with known rate constants. If H2O2 was added to the enzymatic reaction, a stimulation of the production of the hydroxyl radical was obtained. This stimulation was manifested in both the concentration and the rate of formation of the DMPO/hydroxyl radical adduct. Catalase was shown to inhibit formation of the hydroxyl radical adduct, further supporting the formation of hydrogen peroxide as an intermediate during the reduction of oxygen. All three components, ferredoxin, ferredoxin:NADP+ oxidoreductase, and NADPH, were required for reduction. Ferredoxin:NADP+ oxidoreductase reduces ferredoxin, which in turn is responsible for the reduction of oxygen to hydrogen peroxide and ultimately the hydroxyl radical. The effect of transition metal chelators on the DMPO/hydroxyl radical adduct concentration suggests that the reduction of chelated iron by ferredoxin is responsible for the reduction of hydrogen peroxide to the hydroxyl radical via Fenton-type chemistry.
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PMID:The transition metal-mediated formation of the hydroxyl free radical during the reduction of molecular oxygen by ferredoxin-ferredoxin:NADP+ oxidoreductase. 282 73

A minor pathway for cyanamide metabolism catalyzed by catalase is responsible for the conversion of cyanamide to an inhibitor of aldehyde dehydrogenase. Catalase itself is also inhibited by cyanamide. Both the activation of cyanamide by catalase and the inhibition of catalase by cyanamide were blocked in vivo by ethanol pretreatment, suggesting that these two processes are closely linked. Like other catalase oxidation reactions, the catalase mediated activation of cyanamide was inhibited by 3-amino-1,2,4-triazole in vivo and sodium azide in vitro. The relative formation of the active cyanamide metabolite was assessed in vitro by following the loss of yeast aldehyde dehydrogenase activity with time. Inhibition of the yeast enzyme by activated cyanamide was dependent on NAD+ or NADP+, a requirement not fulfilled by NADH or NADPH. Although H2O2 inhibited yeast aldehyde dehydrogenase in vitro and cyanamide inhibited hepatic catalase in vivo, the possible in hepatic H2O2 concentration following cyanamide administration does not account for the effects of cyanamide on ethanol metabolism. While the cyanamide activating enzyme has been identified as catalase, the reaction products of this reaction and, in particular, the structure of the active metabolite involved in the inhibition of aldehyde dehydrogenase remain unknown.
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PMID:Catalase mediated conversion of cyanamide to an inhibitor of aldehyde dehydrogenase. 404 Mar 75

Purified ferredoxin-(cytochrome c)-NADP+ oxidoreductase and xanthine oxidase were found to catalyse the reduction of nitrofurantoin to the free radical. Under aerobic conditions, the nitrofurantoin radical underwent autoxidation to regenerate the parent compound with the concomitant production of superoxide and eventually hydrogen peroxide. The nitrofurantoin radical was also shown to react with hydrogen peroxide to generate a highly reactive species which was capable of oxidising methionine to ethylene. This active oxygen radical appeared to be identical with the crypto-OH . radical, previously proposed as being formed from the analogous reaction of the methyl viologen radical with hydrogen peroxide [R.J. Youngman and E.F. Elstner, FEBS Lett. 129, 265 (1981)]. Catalase inhibited nitrofurantoin-dependent ethylene formation in both enzyme systems, whereas superoxide dismutase was only inhibitory in the xanthine oxidase mediated reaction. Although the primary function of the respective enzyme systems is to generate the nitrofurantoin radical, the xanthine oxidase reaction is markedly more complex than that of ferredoxin-(cytochrome c)-NADP+ oxidoreductase. The differences between the two enzyme reactions appear to be due to the endogenous autoxidation of xanthine oxidase. The aerobic activation of nitrofurantoin by xanthine oxidase involved the superoxide anion as an intermediate, whereas the nitrofuran was directly reduced by ferredoxin-(cytochrome c)-NADP+ oxidoreductase without a requirement for active oxygen species.
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PMID:Mechanisms of oxygen activation by nitrofurantoin and relevance to its toxicity. 629 96

NADPH bound to each Catalase subunit was replaced by NADP+ or by the dehydrogenases inhibitor 3-amino-pyridine-adenine dinucleotide phosphate (AADP). The comparison of the three enzyme forms with respect to the capability to dismutate H2O2, or to oxidize ethanol by a peroxidation process using peroxoacetic acid, showed that the enzyme activity is approximately unchanged whatever the nucleotide bound. On the contrary, the dismutation of peroxoacetic acid drops to zero when NADPH is replaced either by the oxidized NADP+ or by the inhibitor AADP. The spectral changes induced by peroxoacetic acid at the heme Soret region indicate that the three enzyme types are quickly oxidized to Compound I [FeV(O)] and successively reduced by two monoelectron intramolecular reactions leading to Compound II [FeIV(OH)] and finally to the resting state (FeIII). Therefore NADPH bound to Catalase is not essential to catalyze peroxidation processes or H2O2 dismutation, but it is essential to prevent the enzyme denaturation and to catalyze dismutation of peroxides other than H2O2.
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PMID:The function of NADPH bound to Catalase. 808 59