Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.6.99.3 (diaphorase)
 5,903 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Menadione (2-methyl-1,4-naphthoquinone) was used as a model compound to test the hypothesis that thioether conjugates of quinones can be toxic to tissues associated with their elimination through a mechanism involving oxidative stress. Unlike menadione, the glutathione (2-methyl-3-(glutathion-S-yl)-1,4-naphthoquinone; MGNQ) and N-acetyl-L-cysteine (2-methyl-3-(N-acetylcysteine-S-yl)-1,4-naphthoquinone; M(NAC)NQ) thioether conjugates were not able to arylate protein thiols but were still able to redox cycle with cytochrome c reductase/NADH and rat kidney microsomes and mitochondria. Interestingly, menadione and M(NAC)NQ were equally toxic to isolated rat renal epithelial cells (IREC) while MGNQ was nontoxic. The toxicity of both menadione and M(NAC)NQ was preceded by a rapid depletion of soluble thiols and was associated with a depletion of soluble thiols and was associated with a depletion of protein thiols. Treatment of IREC with the glutathione reductase inhibitor, 1,3-bis(2-chloroethyl)-1-nitrosourea, potentiated the thiol depletion and toxicity observed with menadione and M(NAC)NQ indicating the involvement of oxidative stress in this model of renal cell toxicity. The lack of MGNQ toxicity can be attributed to an intramolecular cyclization reaction which destroys the quinone nucleus and therefore eliminates its ability to redox cycle. These findings have important implications with regard to our understanding of the toxic potential of quinone thioether conjugates and of quinone toxicity in general.
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PMID:The toxicity of menadione (2-methyl-1,4-naphthoquinone) and two thioether conjugates studied with isolated renal epithelial cells. 199 Sep 78

A study of the steady-state kinetics of NADH(NADPH)-cytochrome c reductase (FMN-containing) from ale yeast (M. S. Johnson and S. A. Kuby (1985) J. Biol. Chem. 260, 12341-12350) has led to a postulated three-substrate random-ordered hybrid mechanism, where NAD(P)H and FMN add randomly and very likely in a steady-state fashion, followed by an ordered addition of cytochrome c. Kinetic parameters have been derived from this mechanism. Arrhenius plots showed large differences between NADH and NADPH, as the substrate-reductant. Menadione accelerated cytochrome c reduction and also O2 uptake, but vitamin K1 and coenzyme Q10 were ineffective as electron mediators, possibly as a result of their insolubility. With NADPH as the substrate-reductant, the order of the rate of reduction of electron acceptors was ferricyanide greater than DCIP greater than cytochrome c greater than oxygen; with menadione, the specificity sequence was cytochrome c greater than ferricyanide greater than DCIP greater than oxygen. With NADH, the order was ferricyanide greater than cytochrome c greater than oxygen greater than DCIP, which changed to cytochrome c greater than ferricyanide greater than oxygen greater than DCIP on addition of menadione. Cytochrome b5 was also reduced in the absence of oxygen. No transhydrogenase activity was observed, but the reduced thionicotinamide analogs of NADH and NADPH acted as substrates. Superoxide dismutase inhibited cytochrome c reduction in air by 50%, but O2-. was not necessary for cytochrome c reduction, as evidenced by the increase in rate in the absence of O2. The product of the reaction with oxygen appeared to be H2O2.
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PMID:Studies on NADH(NADPH)-cytochrome c reductase (FMN-containing) from yeast: steady-state kinetic properties of the flavoenzyme from top-fermenting ale yeast. 308 Sep 58

The cytotoxicity of menadione (2-methyl-1,4-naphthoquinone) had been investigated using primary cultures of rat hepatocytes. Menadione was found to induce DNA strand breaks which were actively repaired by the cells. Dicoumarol, an inhibitor of DT diaphorase, did not potentiate menadione-induced DNA strand breaks. Neither had metyrapone, an inhibitor of cytochrome P-450 dependent monooxygenases, any effect on the extent of DNA damage. Covalent binding of menadione metabolite(s) to DNA was detected in the cultured hepatocytes and, in addition, hepatic microsomes were also found to metabolize menadione to DNA-binding products. The extent of binding of menadione to DNA in vitro, was markedly decreased by inclusion of the hepatic cytosol fraction, or reduced glutathione, in the incubations. In the presence of dicoumarol, menadione was also found to induce cell membrane damage. It also caused a rapid loss in cellular glutathione which was augmented by the presence of dicoumarol. The results suggest that both the cell membrane damage and DNA damage induced by menadione are mediated by one-electron reduction of the quinone to free radical intermediate(s). DT diaphorase appears to protect the cell from membrane damage, whereas reduced glutathione may have an important role in the prevention of DNA damage.
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PMID:Induction of DNA damage by menadione (2-methyl-1,4-naphthoquinone) in primary cultures of rat hepatocytes. 620 38

NADH dehydrogenase is an iron-sulfur flavoprotein which is isolated and purified from Complex I (mitochondrial NADH: ubiquinone oxidoreductase) by resolution with NaClO4. The activity of the enzyme (followed as NADH: 2-methylnaphthoquinone oxidoreductase) increases linearly with protein concentration (in the range between 0.2 and 1.0 mg/ml) and decreases with aging upon incubation on ice. In the present work a good correlation was found between enzymic activity and labile sulfide content, at least within the limits of sensitivity of the assays employed. Rhodanese (thiosulfate: cyanide sulfurtransferase (EC 2.8.1.1) purified from bovine liver mitochondria was shown to restore, in the presence of thiosulfate, the activity of the partly inactivated NADH dehydrogenase. Concomitantly, sulfur was transferred from thiosulfate to the flavoprotein and incorporated as acid-labile sulfide. Rhodanese-mediated sulfide transfer was directly demonstrated when the reactivation of NADH dehydrogenase was performed in the presence of radioactive thiosulfate (labeled in the outer sulfur) and the 35S-loaded flavoprotein was re-isolated by gel filtration chromatography. The results indicated that the [35S]sulfide was inserted in NADH dehydrogenase and appeared to constitute the structural basis for the increase in enzymic activity.
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PMID:Interaction of rhodanese with mitochondrial NADH dehydrogenase. 640 20

NAD(P)H-cytochrome c reductase activities have been determined in the earthworms, L. rubellus and A. chlorotica, extracts. Menadione (0.35 mM, maximum concentration tested) was found to stimulate the rates of NADPH- and NADH-dependent cytochrome c reduction by three- and twofold, respectively. Superoxide dismutase (SOD) inhibited completely this menadione-mediated stimulation, suggesting that *O2- is involved in the redox cycling of menadione. However, SOD had no effect on the basal activity (activity in the absence of quinone) in the case of NADH-dependent cytochrome c reduction, whereas it partially inhibited the basal activity of NADPH-cytochrome c reduction. This indicates direct electron transfer in the former case and the formation of superoxide anion in the latter. DT-diaphorase, measured as the dicumarol-inhibitable part of menadione reductase activity, was not detectable in the earthworms' extracts. In contrast, it was found that DT-diaphorase represents about 70% of the menadione reductase activities in the freshwater mussel, Dreissena polymorpha. The results of this work suggest that earthworms, compared with mussels, could be more vulnerable to oxidative stress from quinones due to lack, or very low level of DT-diaphorase, an enzyme considered to play a significant role in the detoxification of quinones. On the contrary, mussels have efficient DT-diaphorase, which catalyzes two-electron reduction of menadione directly to hydroquinone, thus circumventing the formation of semiquinone.
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PMID:Menadione enhances oxyradical formation in earthworm extracts: vulnerability of earthworms to quinone toxicity. 1293 5

Conidia of Verticillium albo-atrum Reinke and Berthold, collected from shake cultures grown in Czapek broth, were sonified for 4 or 8 minutes or ground frozen in a mortar to obtain cell-free homogenates. These were assayed for certain enzymes associated with respiratory pathways. Malic dehydrogenase was the most active, glucose-6-P and NADH dehydrogenase were less active, NADH-cytochrome c reductase, NADPH dehydrogenase, and cytochrome oxidase were low in activity, and succinic dehydrogenase and succinic cytochrome c reductase were very low to negligible in activity. No NADH oxidase activity was detected.With the exception of NADH-cytochrome c reductase and possibly succinic dehydrogenase and cytochrome c reductase, there was no evident increase in specific activity of the enzymes during germination. Some NADH-cytochrome c reductase and a small amount of succinic-dehydrogenase and cytochrome c reductase were associated with the particulate fraction from 105,000 x g centrifugation. The other enzymes, including cytochrome oxidase, almost completely remained in the supernatant fraction.Menadione and vitamin K-S(II) markedly stimulated NADH-cytochrome c reductase activity in the supernatant fraction but had much less effect on NADPH-cytochrome c reductase in this fraction or on either of these enzyme systems in the particulate fraction. Electron transport inhibitors affected particulate NADH- and NADPH-cytochrome c reductase activity but had no effect on these in the supernatant fraction.
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PMID:Relative Activities and Characteristics of Some Oxidative Respiratory Enzymes from Conidia of Verticillium albo-atrum. 1665 81

Immortalized differentiated liver cell lines capable of continuous proliferation, and expressing stable liver-specific functions, would be valuable for in vitro toxicity testing in the pharmaceutical, chemical, food and cosmetics industries. Immortalized rat hepatocyte cell lines have been produced by transfection of SV40 DNA by electroporation or calcium phosphate precipitation. Their utility has been assessed by studying the toxicity of a model compound, menadione, and by measuring the activities of DT-diaphorase and NADPH cytochrome c reductase. Enzyme activities and toxicity were compared in freshly isolated hepatocytes, the immortalized cell lines and dedifferentiated HTC hepatoma cells. In HTC cells DT-diaphorase activity was 100-fold elevated compared with freshly isolated hepatocytes. In only one cell line, C2.1.2. (produced by calcium phosphate precipitation), was DT-diaphorase activity increased (twofold) compared with freshly isolated hepatocytes. Menadione caused loss of viability at similar concentrations (40-80 mum) in the immortalized cell lines and 24-hr primary cultures of hepatocytes, whereas HTC cells showed loss of viability only with menadione concentrations above 200 mum. The immortalized lines therefore appear to have potential for predicting toxicity and for menadione this can be correlated with the expression of DT-diaphorase.
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PMID:Immortalized hepatocytes as in vitro model systems for toxicity testing: the comparative toxicity of menadione in immortalized cells, primary cultures of hepatocytes and HTC hepatoma cells. 2065 Feb 56

In the green alga Ankistrodesmus braunii, all the activities associated with the nitrate reductase complex (i.e., NAD(P)H-nitrate reductase, NAD(P)H-cytochrome c reductase and FMNH2-or MVH-nitrate reductase) are nutritionally repressed by ammonia or methylamine. Besides, ammonia or methylamine promote in vivo the reversible inactivation of nitrate reductase, but not of NAD(P)H-cytochrome c reductase. Subsequent removal of the inactivating agent from the medium causes reactivation of the inactive enzyme. Menadione has a striking stimulation on the in vivo reactivation of the inactive enzyme. The nitrate reductase activities, but not the diaphorase activity, can be inactivated in vitro by preincubating a partially purified enzyme preparation with NADH or NADPH. ADP, in the presence of Mg(2+), presents a cooperative effect with NADH in the in vitro inactivation of nitrate reductase. This effect appears to be maximum at a concentration of ADP equimolecular with that of NADH.
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PMID:Studies on the regulation of assimilatory nitrate reductase in Ankistrodesmus braunii. 2442 Jun 58