Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: DrugBank:EXPT00568 (ascorbate)
 23,072 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To clarify the significance of catalase in peroxisomes, we have examined the effect of aminotriazole treatment of rats on the activity of beta-hydroxybutyryl-CoA dehydrogenase in liver peroxisomes. When the effect of H2O2 on the dehydrogenase activity was examined using an extract of liver peroxisomes from aminotriazole-treated rats, the acetoacetyl-CoA-dependent oxidation of NADH was found to increase considerably on the addition of dilute H2O2. Such an effect of H2O2 was not seen on the beta-hydroxybutyryl-CoA-dependent reduction of NAD nor with extracts from untreated animals. We then noticed that similar NADH oxidation was caused non-enzymatically by a mixture of acetoacetyl-CoA and H2O2. The oxidation was dependent on both acetoacetyl-CoA and H2O2, and was blocked by scavengers of oxyradicals such as ascorbate and ethanol. Degradation products formed during the reaction of acetoacetyl-CoA with H2O2 had no NADH oxidizing activity, indicating that effective oxidant(s) were generated during the reaction of H2O2 with acetoacetyl-CoA. No other fatty acyl-CoA so far examined nor acetoacetate could replace acetoacetyl-CoA in this reaction. Therefore, if H2O2 were to be accumulated in peroxisomes, it would decrease both NADH and acetoacetyl-CoA, thus affecting the fatty acyl-CoA beta-oxidation system. These results, together with our previous finding that peroxisomal thiolase was significantly inactivated by H2O2 [Hashimoto, F. & Hayashi, H. (1987) Biochim. Biophys. Acta 921, 142-150] suggest that the role of catalase in peroxisomes is at least in part to protect the fatty acyl-CoA beta-oxidation system from the deleterious action of H2O2.
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PMID:Significance of catalase in peroxisomal fatty acyl-CoA beta-oxidation: NADH oxidation by acetoacetyl-CoA and H2O2. 227 34

The factors necessary to dissociate iron from transferrin in endocytic vesicles and to mobilize the iron across the vesicle membrane were studied in a preparation of endocytic vesicles markedly enriched in transferrin-transferrin receptor complexes isolated from rabbit reticulocytes. Vesicles were prepared with essentially fully saturated transferrin by incubating the reticulocytes with the protonophore carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone prior to incubation with 59Fe, 125I-transferrin with or without fluorescein isothiocyanate labeling. Initiation of acidification by the addition of ATP was sufficient to achieve dissociation of 59Fe from transferrin with a rate constant of 0.054 +/- 0.06 s-1. Mobilization of 59Fe out of the vesicles required, besides ATP, the addition of a reductant with 1 mM ascorbate, allowing approximately 60% mobilization at 10 min with a rate constant of 0.0038 +/- 0.0006 s-1. An NADH:ferricyanide reductase activity could be demonstrated in the vesicles with an activity of 7.1 x 10(-9) mol of NADH reduced per min/mg of vesicle protein. Both dissociation and mobilization were inhibited by N-ethylmaleimide, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone, and monensin. Mobilization, but not dissociation, was inhibited by the permeant Fe(II) chelator alpha,alpha'-dipyridyl. The Fe(III) chelators deferoxamine, diethylenetriaminepentaacetic acid, and apotransferrin did not promote mobilization of dissociated iron in the absence of a reductant. This study establishes the basis for the cellular incorporation of iron through the endocytic pathway in which the endocytic vesicle membrane utilizes, in a sequential way, an acidification system, an iron reduction system, and an Fe(II) transporter system.
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PMID:Mobilization of iron from endocytic vesicles. The effects of acidification and reduction. 232 97

As part of an ongoing study of the role of subcellular fractions on the metabolism of nitroxides, we studied the metabolism of a set of five nitroxides in cytosol derived from rat hepatocytes. The nitroxides were chosen to provide information on the effects of the type of charge and the ring on which the nitroxyl group is located. The rates of reduction were fastest for a six-membered positively charged nitroxide ('CAT-1') and slowest for an anionic five-membered ring nitroxide ('PCA'). Changing levels of glutathione, sulphydryl groups in general, NADPH or NADH had little or no effect on the rates of reduction, while the addition of ascorbate oxidase essentially abolished reduction of the nitroxides. The products of reduction by the cytosol were the corresponding hydroxylamines. The overall rates of reduction of neutral or anionic nitroxides were much slower than those observed with intact cells. We conclude that the primary source of metabolism of nitroxides by cytosol is reduction by ascorbate and that under most conditions reduction of nitroxides in the cytosol is not a major factor in the metabolism of nitroxides by cells.
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PMID:Metabolism of nitroxide spin labels in subcellular fractions of rat liver. II. Reduction in the cytosol. 236 85

Changes in activities of ascorbate free radical (AFR) reductase (NADH:AFR oxidoreductase) and H2O2-dependent NADH oxidation were correlated with levels of insoluble protein in senile cataractous human lenses. The H2O2-dependent NADH oxidation activity was measured to reflect the content of free glutathione. AFR reductase activities in all the cataractous lenses assayed here tended to decrease with increase of insoluble protein contents. A similar tendency in the relationship between lens protein aggregation and H2O2-dependent NADH oxidation activities, i.e. free glutathione contents was recognized in the lenses with pale yellow, yellow or dark yellow nucleus. However, for the highest levels of insoluble protein, some of the brunescent cataractous lenses exhibited very high activities of H2O2-dependent NADH oxidation, and some brunescent lenses had very low activities. From the above results, it is suggested that lens protein aggregates in the brunescent and non-brunescent cataractous lenses may be formed through significantly different oxidation processes, respectively. The possible mechanisms such as free radical reaction and disulfide bond formation are discussed.
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PMID:Activities of ascorbate free radical reductase and H2O2-dependent NADH oxidation in senile cataractous human lenses. 237 70

Glyceryl-ether monooxygenase (1-alkyl-sn-glycerol,tetrahydropteridine: oxygen oxidoreductase, EC 1.14.16.5) catalyzes the oxidative cleavage of 1-O-alkyl glycerol or glycol derivatives to a long-chain aldehyde and the glycerol or glycol derivative. The specificity for tetrahydropterins of a similar, perhaps identical, enzyme that cleaves O-hexadecyl ethylene glycol in rat liver microsomes was examined with the use of an assay based on [1-3H]ethylene glycol formation from 2-hexadecyloxy [1-3H]ethan-1-ol. Several tetrahydropterin derivatives are effective electron donors for this reaction, and 2,4,5-triamino-6-hydroxypyrimidine is somewhat effective, but NADH, NADPH, ascorbate, reduced dichlorophenolindophenol and glutathione are inactive. Tetrahydropterin derivatives differ from each other in apparent Km and apparent Vmax. The order of increasing apparent Km values is tetrahydropterin approximately 6-methyltetrahydropterin approximately tetrahydrobiopterin less than 6.7-dimethyltetrahydropterin less than tetrahydrofolate. The order of increasing apparent Vmax values is tetrahydrofolate approximately tetrahydropterin less than 6-methyltetrahydropterin approximately tetrahydrobiopterin approximately 6,7-dimethyltetrahydropterin. Results obtained with the use of a spectrophotometric assay, in which tetrahydropterin oxidation is coupled to NADH oxidation by dihydropteridine reductase (NAD(P)H: 6,7-dihydropteridine oxidoreductase, EC 1.6.99.7), indicated that the ratio of 6,7-dimethyltetrahydropterin or 6-methyltetrahydropterin oxidized to ether lipid degraded is about 1.1 to 1.3. Unlike cytochrome P-450-dependent hydroxylases, this alkyl glycol-ether monooxygenase is not inhibited by carbon monoxide. 1-O-hexadecyl-rac-glycerol (chimyl alcohol) competitively inhibits the oxidation of the glycol ether indicating that the same enzyme probably catalyzes the oxidation of both O-alkyl glycol and 1-O-alkyl glycerol.
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PMID:Dependence of an alkyl glycol-ether monooxygenase activity upon tetrahydropterins. 237 98

The effect of Ag+ on Na+ pumping by Na(+)-motive NADH-quinone reductase and terminal oxidase has been studied in Bacillus FTU inside-out vesicles. Very low concentrations of Ag+ (C1/2 = 1 x 10(-8) M or 2 x 10(-12) g ion.mg protein-1) are shown to inhibit the uphill Na+ uptake coupled to the oxidation of NADH by fumarate or of ascorbate + TMPD by oxygen but exert no effect on the H+ uptake by the H(+)-motive respiratory chain. Low Ag+ also induces a specific increase in the Na+ permeability of the vesicles. HQNO, added before and not after Ag+, prevents the Ag(+)-induced permeability increase, with effective HQNO concentrations being similar to those inhibiting the uphill Na(+)-uptake coupled to the NADH-fumarate oxidoreduction. Reduction of terminal oxidase by ascorbate + TMPD in the presence of cyanide sensitizes the Na+ permeability to Ag+. It is suggested that low [Ag+], known as a specific inhibitor of electron transport by the Na(+)-motive NADH-quinone reductase, uncouples the electron and Na+ transports so that the Ag(+)-modified NADH-quinone reductase operates as an Na+ channel rather than an Na+ pump. This effect is discussed in connection with the antibacterial action of Ag+.
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PMID:Submicromolar Ag+ increases passive Na+ permeability and inhibits the respiration-supported formation of Na+ gradient in Bacillus FTU vesicles. 238 16

The three steps in the synthesis of aldosterone (11 beta/18-hydroxylations and aldehyde synthetase) were examined in mitochondria from bovine glomerulosa and fasciculata to study the regulation of aldehyde synthetase. Ascorbate plus NADH shows synergism with malate in stimulating aldehyde synthetase without affecting 11 beta/-18-hydroxylations. The concentration of semidehydroascorbate reductase in mitochondria from glomerulosa is more than twice that from fasciculata. We propose that in glomerulosa, ascorbate provides a source of reducing equivalents that specifically support the last step in the synthesis of aldosterone.
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PMID:Ascorbate as a source of reducing equivalents for the synthesis of aldosterone. 239 91

Ascorbate free radical stimulates the growth of human promyelocytic leukemia cells (HL-60) in the presence of a limited amount of serum (1%) when added to the cells under conditions where it is impermeable. Maximum growth stimulation occurs at concentrations from 5 x 10(-9) to 2 x 10(-8) M. Ascorbate mimicks the stimulation effect of its free radical but stimulates at higher concentrations. Autoxidation of ascorbate by oxygen produces its free radical, which apparently causes growth stimulation. Ascorbate could be regenerated by intact cells in vitro, since prevention of autoxidation of ascorbate in the presence of cells is observed. Neither dehydroascorbate nor isoascorbate increases HL-60 cell growth. Short term incubation of cells in the presence of ascorbate free radical induced intracellular NADH oxidation. We propose that the stimulation of growth of HL-60 cells shown here could be caused by activation of the transplasma membrane electron transport system by the ascorbate free radical.
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PMID:Ascorbate free radical stimulates the growth of a human promyelocytic leukemia cell line. 239 60

Protease activity present in aerobically grown cells of Pseudomonas perfectomarina, protease apparently copurified with cytochrome c-552, and trypsin achieved a limited proteolysis of the diheme cytochrome c-552. That partial lysis conferred cytochrome c peroxidase activity upon cytochrome c-552. The removal of a 4000-Da peptide explains the structural changes in the cytochrome c-552 molecule that resulted in the appearance of both cytochrome c peroxidase activity (with optimum activity at pH 8.6) and a high-spin heme iron. The oxidized form of the modified cytochrome c-552 bound cyanide to the high-spin ferric heme with a rate constant of (2.1 +/- 0.1) X 10(3) M-1 s-1. The dissociation constant was 11.2 microM. Whereas the intact cytochrome c-552 molecule can be half-reduced by ascorbate, the cytochrome c peroxidase was not reducible by ascorbate, NADH, ferrocyanide, or reduced azurin. Dithionite reduced the intact protein completely but only half-reduced the modified form. The apparent second-order rate constant for dithionite reduction was (7.1 +/- 0.1) X 10(2) M-1 s-1 for the intact protein and (2.2 +/- 0.1) X 10(3) M-1 s-1 for the modified form. In contrast with other diheme cytochrome c peroxidases, reduction of the low-spin heme was not necessary to permit ligand binding by the high-spin heme iron.
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PMID:Cytochrome c peroxidase activity of a protease-modified form of cytochrome c-552 from the denitrifying bacterium Pseudomonas perfectomarina. 253 41

The nonenzymatic oxidation of NADH was studied spectrophotometrically in the presence of two vanadium compounds, sodium orthovanadate and vanadyl sulfate. At physiological pH 7.4, in 25 mM sodium phosphate buffer, addition of the synthetic thiol, dithioerythritol (DTE) results in a marked increase of NADH oxidation in the presence of sodium orthovanadate, but not in the presence of vanadyl sulfate. Other reductants, such as dithiothreitol and cysteine, can also increase NADH oxidation, whereas glutathione and ascorbate cannot. In all reactions, superoxide dismutase and catalase completely inhibit the vanadium-stimulated oxidation of NADH. Inhibition occurs in a concentration-dependent manner, and the boiled enzymes do not inhibit the thiol reaction. The hydroxyl radical scavenger, thiourea, inhibits the reaction, whereas urea cannot. ESR studies show that the ability of the thiol to reduce vanadate can be correlated with the degree of NADH oxidation. Using spin trapping techniques, hydroxyl radicals are detected during the course of the reaction. Addition of hydrogen peroxide to vanadyl in the presence of DTE greatly increases NADH oxidation; however, no NADH oxidation occurs when hydrogen peroxide is added to vanadyl and ascorbic acid. These results provide a partial explanation for the ability of vanadium compounds to both decrease cellular reducing equivalents and promote lipid peroxidation.
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PMID:Oxidation of NADH by vanadium compounds in the presence of thiols. 254 Jul 16


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