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)

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

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

Heart lipoamide dehydrogenase (LADH) catalyzed redox-cycling and O2-. production by (5-nitro-2-furfurylidene)amino derivatives using NADH as electron donor. NADH was a much more effective electron donor than NADPH for the nitroreductase activity. O2-. production was demonstrated by cytochrome c reduction, adrenochrome formation and the effect of superoxide dismutase. Under optimum conditions, nitroreductase activity was about 1% of LADH activity. One electron oxygen reduction and NADH oxidation correlated in 2:1 stoichiometry. The nitroreductase kinetics was in accordance with an ordered bi-bi mechanism. Nitrofuran derivatives bearing unsaturated five- or six-membered nitrogen heterocycles were more effective substrates than those bearing other groups, namely nifurtimox, nitrofurazone, nitrofurantoin and 5-nitro-2-furoic acid. Other nitro compounds (chloramphenicol, benznidazole, 2-nitroimidazole and 5-nitroindole) were ineffective. With the triazole, traizine and imidazole nitrofuran derivatives, the nitroreductase pH curve showed a maximum at pH 8.8, different from the pH optimum for the lipoamide reductase and diaphorase activities. Spectroscopic observations demonstrated pH-dependent structural changes in the triazole(I) and triazine derivatives which would affect their behavior as nitroreductase substrates. The nitroreductase activity was inhibited by p-chloromercuribenzoate and enhanced by cadmium and arsenite, whereas the NADH-induced LADH inactivation failed to affect the nitroreductase activity. In the absence of oxygen. LADH catalyzed nitrofuran reduction to products more reduced than the nitroanion, which were not reoxidized by oxygen. The anaerobic nitrofuran reduction was inhibited by cadmium and arsenite. The assayed nitrofuran compounds did not inhibit LADH lipoamide reductase activity, at variance with their action on glutathione reductase (Grinblat et al., Biochem Pharmacol 38: 767-772, 1989).
...
PMID:Catalysis of nitrofuran redox-cycling and superoxide anion production by heart lipoamide dehydrogenase. 217 92

Superoxide (.O2-) production by the NADPH oxidase of a membrane fraction derived from rabbit peritoneal neutrophils activated by 4 beta-phorbol 12-myristate 13-acetate (PMA) was studied at 25 degrees C under different conditions, and measured by the superoxide dismutase inhibitable reduction of cytochrome c. Whereas PMA-activated rabbit neutrophils incubated in a glucose-supplemented medium exhibited a substantial rate of production of .O2-, the membranes prepared by sonication of the activated neutrophils were virtually unable to generate .O2- in the presence of NADPH. Instead, they exhibited an NADPH-dependent diaphorase activity, measured by the superoxide-dismutase-insensitive reduction of cytochrome c. Upon addition of arachidonic acid, which is known to elicit oxidase activation, the NADPH diaphorase activity of the rabbit neutrophil membranes vanished and was stoichiometrically replaced by an NADPH oxidase activity. The emerging oxidase activity was fully sensitive to iodonium biphenyl, a potent inhibitor of the respiratory burst, whereas the diaphorase activity was not affected. Addition of 0.1% Triton X-100 or an excess of arachidonic acid, acting as detergent, resulted in the reappearance of the diaphorase activity at the expense of the oxidase activity. These results indicate that the diaphorase-oxidase transition is reversible. When the rabbit neutrophil membranes were supplemented with rabbit neutrophil cytosol, guanosine 5'-[gamma-thio]triphosphate and Mg2+, in addition to arachidonic acid, not only the NADPH diaphorase activity disappeared, but the emerging NADPH oxidase activity was markedly enhanced (about 10 times compared to that of membranes treated with arachidonic acid alone). The diaphorase-oxidase transition was accompanied by a 10-fold increase in the Km for NADPH, suggesting a change of conformation propagated to the NADPH-binding site during the transition. The treatment of PMA-activated rabbit neutrophils with cross-linking reagents, like glutaraldehyde or 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide, prevented the loss of the PMA-elicited oxidase activity upon disruption of the cells by sonication, suggesting that the interactions between the components of the oxidase complex are stabilized by cross-linking.
...
PMID:Respiratory burst of rabbit peritoneal neutrophils. Transition from an NADPH diaphorase activity to an .O2(-)-generating oxidase activity. 217 79

Many anticancer drugs exert their cytotoxic effects via formation of oxygen free radicals. Cellular thiols, glutathione (GSH)-dependent enzymes and other redox enzymes are involved in the metabolism of these anticancer drugs and of the oxygen free radicals that may be generated during their metabolism. We quantified these biochemical parameters in cytosol from human ovarian tissues. We compared non-protein thiol levels, GSH transferase, GSH peroxidase, superoxide dismutase, catalase, DT diaphorase and aldehyde dehydrogenase activity in serous ovarian tumors (n = 15), other malignant ovarian tumors (n = 12), benign ovarian tissue (n = 10) and histologically normal ovarian tissue (n = 12). Mean GSH transferase and DT diaphorase activities were similar in serous and other malignant ovarian tumors. GSH transferase activity was decreased in malignant tissues relative to normal and benign tissues. Mean DT diaphorase and superoxide dismutase activities were increased in the malignant tissues, although this was not statistically significant. The mean levels of all enzymes except superoxide dismutase and aldehyde dehydrogenase in benign tissues were fairly similar to the mean levels found in normal tissue samples. Tissues from patients with serous ovarian tumors, who had received cyclophosphamide and cisplatin prior to surgery, also were analyzed (n = 7). Except for aldehyde dehydrogenase, all the parameters measured were decreased in these samples relative to serous tissue from untreated patients. These biochemical analyses may be useful in understanding the mechanisms involved in the response to chemotherapy.
...
PMID:Detoxifying enzymes in human ovarian tissues: comparison of normal and tumor tissues and effects of chemotherapy. 239 58

Previous studies with Adriamycin-sensitive and -resistant (ADRR) MCF-7 human breast tumor cell lines indicated that Adriamycin formed significantly less hydroxyl radical (.OH) as the result of enhanced detoxification of reactive oxygen intermediates in the ADRR cell line. In order to further define the sites of drug activation and the role of detoxification mechanisms in free radical levels, subcellular fractions were isolated from these two cell lines and free radical formation in the presence of Adriamycin was examined by using electron spin resonance spectroscopy. Studies reported here show that considerable NADPH-cytochrome P-450 reductase and NADH dehydrogenase activities were present in microsomes and mitochondria, respectively, and in nuclei obtained from these cells, and the relative activity of NADH dehydrogenase was 2-fold higher in the mitochondrial fraction of ADRR cells compared to the mitochondrial fraction from the parental wild type cells. In the presence of Adriamycin and a reducing cofactor (NADPH or NADH), Adriamycin semiquinone free radical, superoxide anion, and .OH were detected in all these fractions. Although only a small difference in the relative amount of oxy radical formation was detected in tumor microsomes, both mitochondria and nuclei of ADRR cells showed an overall 2-fold decreased formation of oxy radicals. The formation of the free radicals was significantly inhibited by superoxide dismutase, catalase, and dimethyl sulfoxide, indicating that free .OH generation was both superoxide and hydrogen peroxide dependent. The addition of purified glutathione peroxidase likewise inhibited .OH formation in a dose-dependent fashion. Similarly, when the lysate from ADRR cells, which contains 12- to 14-fold more glutathione peroxidase than Adriamycin-sensitive cells, was added to reaction mixtures containing Adriamycin-sensitive cells and Adriamycin, the .OH formation was diminished. Decreased free radical formation in nuclei and mitochondria, as a result of detoxification of hydrogen peroxide by glutathione peroxidase, may be significant in the protection of ADRR cells from Adriamycin-induced cell killing.
...
PMID:Adriamycin activation and oxygen free radical formation in human breast tumor cells: protective role of glutathione peroxidase in adriamycin resistance. 254 60

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

We examined the properties of neuronal NADPH-diaphorase in sections of rat striatum, using histochemical procedures. NADPH-diaphorase histochemistry stained discrete populations of central neurons and provided a Golgi-like image of the neurons exhibiting this activity. The NADPH-diaphorase reaction appeared to be enzyme catalyzed, since it was abolished by pre-treatment with proteases, heat, and acid or alkaline denaturation. Under anaerobic conditions, any tetrazolium salt with a redox potential more positive than NADPH could be reduced by the enzyme. NADPH-diaphorase activity was sensitive to inhibition by sulfhydryl reagents but was unaffected by metal chelators, superoxide dismutase, and catalase. Therefore, the enzyme is unlikely to be a metalloenzyme or to reduce tetrazoliums by producing superoxide anions or hydrogen peroxide. Various analogues of beta-NADPH could be used by the enzyme; however, beta-NADH, which can be used by DT-diaphorase, was ineffective. The enzyme was also resistant to dicumarol, an inhibitor of DT-diaphorase activity. Electron microscopy indicated that the NADPH-diaphorase reaction resulted in staining of various membranous organelles. We conclude that neuronal NADPH-diaphorase is a membrane-bound enzyme distinct from DT-diaphorase and other known enzymes with diaphorase activity. The histochemical characteristics presented here should now enable meaningful biochemical studies of neuronal NADPH-diaphorase to be undertaken.
...
PMID:Histochemical characterization of neuronal NADPH-diaphorase. 270 1

Blood samples from a female sheep-goat hybrid and its back-cross male offspring were tested for electrophoretic variants of plasma albumin, transferrin and esterase, and of red cell carbonic anhydrase, nucleoside phosphorylase, NADH-diaphorase, 'X'-protein, superoxide dismutase, malic enzyme and haemoglobin. Red cells were also tested for blood group antigens. Both animals showed variants that could not be attributed to either sheep or goat alone, thus confirming previous chromosomal data that the female was a genuine sheep-goat hybrid.
...
PMID:Blood genetic marker studies of a sheep-goat hybrid and its back-cross offspring. 275 69

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


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

---