Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:1.6.99.3 (diaphorase)
5,903 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Treatment of rat liver microsomes with alkaline phosphatase results in a loss in the FMN but not the FAD flavin prosthetic group of NADPH-cytochrome P-450 reductase (Taniguchi, H. and Pyerin, W. (1987) Biochim. Biophys. Acta 912, 295-307). Experiments were carried out to evaluate the effect of preventing electron transfer from the FADH2 to FMN component of the reductase, and subsequent mixed function oxidase activity, on reduction of ferric chelates, production of H2O2, and the generation of .OH-like species by microsomes. Treatment with alkaline phosphatase was confirmed to decrease NADPH-cytochrome c, but not NADPH-ferricyanide, reductase activity by microsomes and by purified NADPH cytochrome P-450 reductase. The oxidation of hydroxyl radical scavenging agents by microsomes and reductase was decreased by the alkaline phosphatase treatment in accordance with the decline in cytochrome c reductase activity. This decrease in hydroxyl radical production occurred in the presence of various ferric chelate catalysts. Rates of microsomal reduction of the ferric chelates were also inhibited after alkaline phosphatase treatment. Production of H2O2 was decreased in accordance to the fall in cytochrome c reductase activity and .OH production. Rates of H2O2 production appeared to be rate-limiting for the overall generation of .OH as the addition of an external H2O2-generating system stimulated .OH production as well as prevented the decline in .OH production caused by the alkaline phosphatase treatment. These results suggest that both the FAD and FMN flavin prosthetic groups of the reductase contribute towards the reduction of various ferric chelates. However, loss of the FMN component and activities dependent on electron transfer from this prosthetic group result in a decrease in H2O2 production, which appears to be responsible for the decline in the generation of .OH-like species by microsomes after treatment with alkaline phosphatase.
...
PMID:Inhibition of the oxidation of hydroxyl radical scavenging agents after alkaline phosphatase treatment of rat liver microsomes. 190 77

The thyroid plasma membrane contains a Ca2(+)-regulated NADPH-dependent H2O2 generating system which provides H2O2 for the thyroid peroxidase-catalyzed biosynthesis of thyroid hormones. The plasma membrane fraction contains a Ca2(+)-independent cytochrome c reductase activity which is not inhibited by superoxide dismutase. But it is not known whether H2O2 is produced directly from molecular oxygen (O2) or formed via dismutation of super-oxide anion (O2-). Indirect evidence from electron scavenger studies indicate that the H2O2 generating system does not liberate O2-, but studies using the modified peroxidase, diacetyldeuteroheme horseradish peroxidase, to detect O2- indicate that H2O2 is provided via the dismutation of O2-. The present results provide indirect evidence that the cytochrome c reductase activity is not a component of the NADPH-dependent H2O2 generator, since it was removed by washing the plasma membranes with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid without affecting H2O2 generation. Spectral studies with diacetyldeuteroheme-substituted horseradish peroxidase showed that the thyroid NADPH-dependent H2O2 generator does not catalyze superoxide anion formation. The O2- adduct compound (compound III) was formed but was completely inhibited by catalase, indicating that the initial product was H2O2. The rate of NADPH oxidation also increased in the presence of diacetylheme peroxidase. This increase was blocked by catalase and was greatly enhanced by superoxide dismutase. The O2- adduct compound (compound III) was produced in the presence of NADPH when glucose-glucose oxidase (which does not produce O2-) was used as the H2O2 generator. NADPH oxidation occurred simultaneously and was enhanced by superoxide dismutase. We conclude that O2- formation occurs in the presence of an H2O2 generator, diacetylheme peroxidase and NADPH, but that it is not the primary product of the H2O2 generator. We suggest that O2- formation results from oxidation of NADPH, catalyzed by the diacetylheme peroxidase compound I, producing NADP degree, which in turn reacts with O2 to give O2-.
...
PMID:Mechanism of hydrogen peroxide formation catalyzed by NADPH oxidase in thyroid plasma membrane. 199 28

Ischemia and reperfusion causes severe mitochondrial damage, including swelling and deposits of hydroxyapatite crystals in the mitochondrial matrix. These crystals are indicative of a massive influx of Ca2+ into the mitochondrial matrix occurring during reoxygenation. We have observed that mitochondria isolated from rat hearts after 90 minutes of anoxia followed by reoxygenation, show a specific inhibition in the electron transport chain between NADH dehydrogenase and ubiquinone in addition to becoming uncoupled (unable to generate ATP). This inhibition is associated with an increased H2O2 formation at the NADH dehydrogenase level in the presence of NADH dependent substrates. Control rat mitochondria exposed for 15 minutes to high Ca2+ (200 nmol/mg protein) also become uncoupled and electron transport inhibited between NADH dehydrogenase and ubiquinone, a lesion similar to that observed in post-ischemic mitochondria. This Ca(2+)-dependent effect is time dependent and may be partially prevented by albumin, suggesting that it may be due to phospholipase A2 activation, releasing fatty acids, leading to both inhibition of electron transport and uncoupling. Addition of arachidonic or linoleic acids to control rat heart mitochondria, inhibits electron transport between Complex I and III. These results are consistent with the following hypothesis: during ischemia, the intracellular energy content drops severely, affecting the cytoplasic concentration of ions such as Na+ and Ca2+. Upon reoxygenation, the mitochondrion is the only organelle capable of eliminating the excess cytoplasmic Ca2+ through an electrogenic process requiring oxygen (the low ATP concentration makes other ATP-dependent Ca2+ transport systems non-operational).(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Mitochondrial generation of oxygen radicals during reoxygenation of ischemic tissues. 206 Aug 40

Bovine heart submitochondrial particles (SMP) were exposed to continuous fluxes of hydroxyl radical (.OH) alone, superoxide anion radical (O2-) alone, or mixtures of .OH and O2-, by gamma radiolysis in the presence of 100% N2O (.OH exposure), 100% O2 + formate (O2- exposure), or 100% O2 alone (.OH + O2- exposure). Hydrogen peroxide effects were studied by addition of pure H2O2. NADH dehydrogenase, NADH oxidase, succinate dehydrogenase, succinate oxidase, and ATPase activities (Vmax) were rapidly inactivated by .OH (10% inactivation at 15-40 nmol of .OH/mg of SMP protein, 50-90% inactivation at 600 nmol of .OH/mg of SMP protein) and by .OH + O2- (10% inactivation at 20-80 nmol of .OH + O2-/mg of SMP protein, 45-75% inactivation at 600 nmol of .OH + O2-/mg of SMP protein). Importantly, O2- was a highly efficient inactivator of NADH dehydrogenase, NADH oxidase, and ATPase (10% inactivation at 20-50 nmol of O2-/mg of SMP protein, 40% inactivation at 600 nmol of O2-/mg of SMP protein), a mildly efficient inactivator of succinate dehydrogenase (10% inactivation at 150 nmol of O2-/mg of SMP protein, 30% inactivation at 600 nmol of O2-/mg of SMP protein), and a poor inactivator of succinate oxidase (less than 10% inactivation at 600 nmol of O2-/mg of SMP protein). H2O2 partially inactivated NADH dehydrogenase, NADH oxidase, and cytochrome oxidase, but even 10% loss of these activities required at least 500-600 nmol of H2O2/mg of SMP protein. Cytochrome oxidase activity (oxygen consumption supported by ascorbate + N,N,N',N'-tetramethyl-p-phenylenediamine) was remarkably resistant to oxidative inactivation, with less than 20% loss of activity evident even at .OH, O2-, OH + O2-, or H2O2 concentrations of 600 nmol/mg of SMP protein. Cytochrome c oxidase activity, however (oxidation of, added, ferrocytochrome c), exhibited more than a 40% inactivation at 600 nmol of .OH/mg of SMP protein. The .OH-dependent inactivations reported above were largely inhibitable by the .OH scavenger mannitol. In contrast, the O2(-)-dependent inactivations were inhibited by active superoxide dismutase, but not by denatured superoxide dismutase or catalase. Membrane lipid peroxidation was evident with .OH exposure but could be prevented by various lipid-soluble antioxidants which did not protect enzymatic activities at all.(ABSTRACT TRUNCATED AT 400 WORDS)
...
PMID:The oxidative inactivation of mitochondrial electron transport chain components and ATPase. 216 88

Dopamine (DA) is rapidly oxidized by Mn3(+)-pyrophosphate to its cyclized o-quinone (cDAoQ), a reaction which can be prevented by NADH, reduced glutathione (GSH) or ascorbic acid. The oxidation of DA by Mn3+, which appears to be irreversible, results in a decrease in the level of DA, but not in a formation of reactive oxygen species, since oxygen is neither consumed nor required in this reaction. The formation of cDAoQ can initiate the generation of superoxide radicals (O2-.) by reduction-oxidation cycling, i.e. one-electron reduction of the quinone by various NADH- or NADPH-dependent flavoproteins to the semiquinone (QH.), which is readily reoxidized by O2 with the concomitant formation of O2-.. This mechanism is believed to underly the cytotoxicity of many quinones. Two-electron reduction of cDAoQ to the hydroquinone can be catalyzed by the flavoprotein DT diaphorase (NAD(P)H:quinone oxidoreductase). This enzyme efficiently maintains DA quinone in its fully reduced state, although some reoxidation of the hydroquinone (QH2) is observed (QH2 + O2----QH. + O2-. + H+; QH. + O2----Q + O2-.). In the presence of Mn3+, generated from Mn2+ by O2-. (Mn2+ + 2H+ + O2-.----Mn3+ + H2O2) formed during the autoxidation of DA hydroquinone, the rate of autoxidation is increased dramatically as is the formation of H2O2. Furthermore, cDAoQ is no longer fully reduced and the steady-state ratio between the hydroquinone and the quinone is dependent on the amount of DT diaphorase present. The generation of Mn3+ is inhibited by superoxide dismutase (SOD), which catalyzes the disproportionation of O2-. to H2O2 and O2. It is noteworthy that addition of SOD does not only result in a decrease in the amount of H2O2 formed during the regeneration of Mn3+, but, in fact, prevents H2O2 formation. Furthermore, in the presence of this enzyme the consumption of O2 is low, as is the oxidation of NADH, due to autoxidation of the hydroquinone, and the cyclized DA o-quinone is found to be fully reduced. These observations can be explained by the newly-discovered role of SOD as a superoxide:semiquinone (QH.) oxidoreductase catalyzing the following reaction: O2-. + QH. + 2H+----QH2 + O2. Thus, the combination of DT diaphorase and SOD is an efficient system for maintaining cDAoQ in its fully reduced state, a prerequisite for detoxication of the quinone by conjugation with sulfate or glucuronic acid. In addition, only minute amounts of reactive oxygen species will be formed, i.e. by the generation of O2-., which through disproportionation to H2O2 and further reduction by ferrous ions can be converted to the hydroxyl radical (OH.). Absence or low levels of these enzymes may create an oxidative stress on the cell and thereby initiate events leading to cell death.
...
PMID:On the mechanism of the Mn3(+)-induced neurotoxicity of dopamine:prevention of quinone-derived oxygen toxicity by DT diaphorase and superoxide dismutase. 255 82

The quinonoid anthracycline, doxorubicin (Adriamycin) is a potent anti-neoplastic agent whose clinical use is limited by severe cardiotoxicity. Mitochondrial damage is a major component of this cardiotoxicity, and rival oxidative and non-oxidative mechanisms for inactivation of the electron transport chain have been proposed. Using bovine heart submitochondrial preparations (SMP) we have now found that both oxidative and non-oxidative mechanisms occur in vitro, depending solely on the concentration of doxorubicin employed. Redox cycling of doxorubicin by Complex I of the respiratory chain (which generates doxorubicin semiquinone radicals, O2-, H2O2, and .OH) caused a 70% decrease in the Vmax. for NADH dehydrogenase during 15 min incubation of SMP, and an 80% decrease in NADH oxidase activity after 2 h incubation. This inactivation required only 25-50 microM-doxorubicin and represents true oxidative damage, since both NADH (for doxorubicin redox cycling) and oxygen were obligatory participants. The damage appears localized between the NADH dehydrogenase flavin (site of doxorubicin reduction) and iron-sulphur centre N-1. Succinate dehydrogenase, succinate oxidase, and cytochrome c oxidase activities were strongly inhibited by higher doxorubicin concentrations, but this phenomenon did not involve doxorubicin redox cycling (no NADH or oxygen requirement). Doxorubicin concentrations of 0.5 mM were required for 50% decreases in these activities, except for cytochrome c oxidase which was only 30% inhibited following incubation with even 1.0 mM-doxorubicin. Our results indicate that low concentrations of doxorubicin (50 microM or less) can catalyse a site-specific oxidative damage to the NADH oxidation pathway. In contrast, ten-fold higher doxorubicin concentrations (or more) are required for non-oxidative inactivation of the electron transport chain; probably via binding to cardiolipin and/or generalized membrane chaotropic effects. The development of agents to block doxorubicin toxicity in vivo will clearly require detailed clinical studies of doxorubicin uptake in the heart.
...
PMID:Oxidative and non-oxidative mechanisms in the inactivation of cardiac mitochondrial electron transport chain components by doxorubicin. 271 42

The production of potent oxygen radicals by microsomal reaction systems has been well characterized. Relatively little attention has been paid to generation of oxygen radicals by liver nuclei, or to the interaction of nuclei with different ferric complexes to catalyze NADH- or NADPH-dependent production of reactive oxygen intermediates. Intact rat liver nuclei were capable of catalyzing an iron-dependent production of .OH as reflected by the oxidation of .OH scavenging agents such as 2-keto-4-thiomethylbutyrate, dimethyl sulfoxide, and t-butyl alcohol. Inhibition of .OH production by catalase implicates H2O2 as the precursor of .OH generated by the nuclei, whereas superoxide dismutase had only a partially inhibitory effect. The production of .OH with either cofactor was striking increased by addition of ferric-EDTA or ferric-diethylenetriamine-pentaacetic acid (DTPA) whereas ferric-ATP and ferric-citrate were not effective catalysts. All these ferric complexes were reduced by the nuclei in the presence of either NADPH or NADH. The pattern of iron chelate effectiveness in catalyzing lipid peroxidation by nuclei was opposite to that of .OH production; with either NADH or NADPH, nuclear lipid peroxidation was increased by the addition of ferric ammonium sulfate, ferric-ATP, or ferric-citrate, but not by ferric-EDTA or ferric-DTPA. NADPH-dependent nuclear lipid peroxidation was insensitive to catalase, superoxide dismutase, or .OH scavengers; the NADH-dependent reaction showed a partial sensitivity (30 to 40%) to these additions. The overall patterns of .OH production and lipid peroxidation by the nuclei are similar to those shown by microsomes, e.g., effect of ferric complexes, sensitivity to antioxidants; however, rates with the nuclei are less than 20% those of microsomes, which reflect the lower activities of NADPH- and NADH-cytochrome c reductase in the nuclei. The potential for nuclei to reduce ferric complexes and catalyze production of .OH-like species may play a role in the susceptibility of the genetic material to oxidative damage under certain conditions since such radicals would be produced site-directed and not exposed to cellular antioxidants.
...
PMID:Interaction of ferric complexes with rat liver nuclei to catalyze NADH-and NADPH-Dependent production of oxygen radicals. 277 54

The possible role of hemoglobin in the sulfoxidation of chlorpromazine is still a controversial subject. Therefore this sulfoxidation was investigated with purified oxyhemoglobin and methemoglobin under various conditions: (i) in phosphate buffer pH 6.5; (ii) in monooxygenase mimicking systems with electron donors like ascorbic acid and NADPH, the last, with and without an electron carrier like methylene blue and cytochrome c reductase; (iii) in the presence of H2O2. Only in the presence of H2O2 chlorpromazine was converted into chlorpromazine sulfoxide in a considerable amount. This so-called peroxidase activity of hemoglobin appeared not to be based on a Fenton-type reaction. An oxidized reactive form of hemoglobin (i.e. ferrylhemoglobin) is responsible for the sulfoxidation. In the other systems only with ascorbic acid some chlorpromazine sulfoxide was produced. This is probably due to the production of H2O2 and the subsequent peroxidase activity of hemoglobin. Chlorpromazine enhanced the autoxidation of oxyhemoglobin, without being transformed itself.
...
PMID:Is hemoglobin a catalyst for sulfoxidation of chlorpromazine? An investigation with isolated purified hemoglobin and hemoglobin in monooxygenase and peroxidase mimicking systems. 281 48

5-(4-Nitrophenyl)penta-2,4-dienal (NPPD) stimulated NADPH-supported oxygen consumption by rat liver microsomes in a concentration-dependent manner. The NPPD stimulation of O2 uptake was not inhibited by metyrapone and was decreased in the presence of NADP+ and p-hydroxymercuribenzoate. These observations suggest that the NPPD initial reduction step is mediated by NADPH-cytochrome P-450 reductase and not by cytochrome P-450. Spin-trapping studies using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) revealed the formation of superoxide anion upon incubation of NPPD, NADPH, DMPO and rat liver microsomes. Hydrogen peroxide generation was also detected in these incubations, thus confirming redox cycling of NPPD under aerobic conditions. NPPD stimulated oxygen consumption, superoxide anion formation and hydrogen peroxide generation by rat kidney, testes and brain microsomes. Other enzymes capable of nitroreduction (NADH dehydrogenase, xanthine oxidase, glutathione reductase, and NADP+ ferredoxin oxidoreductase) were also found to stimulate redox cycling of NPPD. The ability of NPPD to induce superoxide anion and hydrogen peroxide formation might play a role in its reported mutagenicity.
...
PMID:Generation of superoxide anion and hydrogen peroxide during redox cycling of 5-(4-nitrophenyl)-penta-2,4-dienal by mammalian microsomes and enzymes. 283 86

Though all the streptonigrin derivatives with modifications in the carboxyl group on C2' were active as electron acceptors in the oxidation of NADH by Clostridium kluyveri diaphorase as well as streptonigrin, the glycine derivative did not show any marked effect on the KCN-insensitive oxidation of glutamate by rat liver mitochondria, suggesting a poor membrane transport of the glycine derivative. Sakyomicin A also induced the KCN-insensitive oxidation of glutamate by mitochondria, while a trace activity was observed by mitomycin C and the effect of doxorubicin was negligible. Like streptonigrin, the autoxidation of a reduced form (hydroquinone) of sakyomicin A to a quinone accompanied the generation of H2O2. However, exogenous NADH was oxidized by mitochondria in the presence of sakyomicin A but not streptonigrin.
...
PMID:Effects of streptonigrin derivatives and sakyomicin A on the respiration of isolated rat liver mitochondria. 287 95


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---