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Query: UNIPROT:Q8NEX9 (reductase)
 26,410 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ribonucleoside diphosphate reductase subunits B1 and B2 and ether-permeabilized cell activities of Escherichia coli increase in parallel during thymine deprivation. Thioredoxin and thioredoxin reductase activities are not affected by thymine deprivation.
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PMID:Coordinate control of the synthesis of ribonucleoside diphosphate reductase components in Escherichia coli. 40 Aug 2

The thioredoxin/thioredoxin reductase system has been studied as regenerative machinery for proteins inactivated by oxidative stress in vitro and in cultured endothelial cells. Mammalian glyceraldehyde-3-phosphate dehydrogenase was used as the main model enzyme for monitoring the oxidative damage and the regeneration. Thioredoxin and its reductase purified from bovine liver were used as the regenerating system. The physiological concentrations (2-14 microM) of reduced thioredoxin, with 0.125 microM thioredoxin reductase and 0.25 mM NADPH, regenerated H2O2-inactivated glyceraldehyde-3-phosphate dehydrogenase and other mammalian enzymes almost completely within 20 min at 37 degrees C. Although the treatment of endothelial cells with 0.2-12 mM H2O2 for 5 min resulted in a marked decrease in the activity of glyceraldehyde-3-phosphate dehydrogenase, it had no effect on the activities of thioredoxin and thioredoxin reductase. Essentially all of the thioredoxin in endothelial cells at control state was in the reduced form and 70-85% remained in the reduced form even after the H2O2 treatment. The inactivated glyceraldehyde-3-phosphate dehydrogenase in a cell lysate prepared from the H2O2-treated endothelial cells was regenerated by incubating the lysate with 3 mM NADPH at 37 degrees C and the antiserum raised against bovine liver thioredoxin inhibited the regeneration. The inhibition of thioredoxin reductase activity by 13-cis-retinoic acid resulted in a decrease in the regeneration of glyceraldehyde-3-phosphate dehydrogenase in the H2O2-treated endothelial cells. The present findings provide evidence that thioredoxin is involved in the regeneration of proteins inactivated by oxidative stress in endothelial cells.
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PMID:Thioredoxin regenerates proteins inactivated by oxidative stress in endothelial cells. 142 98

Thioredoxin is a small oxidation-reduction (redox) mediator protein. Its reduction by NADPH is catalyzed by the flavoenzyme thioredoxin reductase. Site-directed mutagenesis has provided forms of the reductase in which Cys135 and Cys138 have each been changed to a serine residue (Prongay, A. J., Engelke, D. R., and Williams, C. H., Jr. (1989) J. Biol. Chem. 264, 2656-2664). Cys135 and Cys138 form the redox-active disulfide in the oxidized enzyme. The redox properties of the two altered forms of Escherichia coli thioredoxin reductase have been determined from pH 6.0 to 9.0. Photoreduction of TRR(Ser135,Cys138) produces the blue, neutral semiquinone species, which disproportionates (Kf = 0.73) to an apparent maximum of 29% of the total enzyme as the semiquinone. In contrast, the semiquinone formed on TRR(Cys135,Ser138) during a photoreductive titration does not disproportionate and 70% of the enzyme is stabilized as the semiquinione. Reductive titrations have demonstrated that 1 mol of sodium dithionite (2 electrons)/mol of FAD is required to fully reduce TRR(Ser135,Cys138) whereas 2 mol of dithionite/mol of FAD are required to fully reduce TRR(Cys135,Ser138). The oxidation-reduction midpoint potentials for the 1-electron and 2-electron reductions of TRR(Ser135,Cys138) have been determined by NADH/NAD+ titrations in the presence of a mediator, benzyl viologen. The midpoint potential for the 2-electron reduction of TRR(Ser135,Cys138) is -280 mV, at pH 7.0 and 20 degrees C. Thus, the redox potential is similar to that of the FAD/FADH2 couple in the dithiol form of wild type enzyme, -270 mV (corrected to 20 degrees C) (O'Donnell, M. E., and Williams, C. H., Jr. (1983) J. Biol. Chem. 258, 13795-13805). The delta Em/delta pH is -57.1 mV, which corresponds to a proton stoichiometry of 2 H+/2 e-.A maximum of 19% of the enzyme forms a stable semiquinone species during the titration, and the potentials for the oxidized enzyme/semiquinone couple, E2, and the semiquinone/reduced enzyme couple, E1, are -306 and -256 mV, respectively, at pH 7.0 and 20 degrees C. These studies provide evidence that the residue at position 138 exerts a greater effect on the FAD than does the residue at position 135.
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PMID:Oxidation-reduction properties of Escherichia coli thioredoxin reductase altered at each active site cysteine residue. 146 18

The reduction of Escherichia coli thioredoxin by thioredoxin reductase was studied by stopped-flow spectrophotometry. The reaction showed no dependence on thioredoxin concentration, indicating that complex formation was rapid and occurred during the dead time of the instrument. The kobs for the reaction of approximately 20 s-1 probably reflects the rate of electron transfer from thioredoxin reductase to thioredoxin and agrees with the kcat observed by steady-state kinetics. The reaction rate was unaffected by increasing the ionic strength, suggesting a lack of electrostatic stabilization in the interaction of the two proteins. A mutant thioredoxin in which a positively charged lysine in the active-site region was changed to a glutamic acid residue resulted in an electrostatic destabilization. Thioredoxin K36E was still a substrate for the reductase, but binding was impaired so that the rate could be measured by stopped-flow techniques as reflected by a dependence on protein concentration. Raising the ionic strength in this reaction served to shield the negative charge and increased the rate of binding to the reductase.
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PMID:Kinetics of electron transfer from thioredoxin reductase to thioredoxin. 199 79

In yeast, mutations in six different loci (MET1, MET4, MET8, MET16, MET22, and MET25) have been reported to result in the absence of 3'-phosphoadenylylsulfate (PAPS) reductase activity. In the present study, we show that MET16 is the structural gene for PAPS reductase and that the yeast and the Escherichia coli enzymes display significant similarities. Thioredoxin has been implicated in the reduction of PAPS in Saccharomyces cerevisiae as well as in E. coli. One of the generally accepted mechanisms for the action of thioredoxin as a hydrogen donor involves a redox-active sulfhydryl group in the catalytic site of PAPS reductase. However, the present study shows that the site-directed mutagenesis of the unique cysteine from PAPS reductase leads to an enzyme which remains active in vivo. This result would rather support the hypothesis of thioredoxin playing the role of a thiol carrier in the reduction of PAPS into sulfite. Strains separately mutated in the six different loci cited above were examined for the expression of different genes. A mutation in the MET4 gene abolishes transcription of both genes MET16 and MET25. In contrast, mutations in MET1, MET8, and MET25 do not impair MET16 transcription, yet strains bearing these mutations are devoid of PAPS reductase activity. To account for the latter result, we postulate that the enzymes involved in sulfate assimilation may occur as a multienzyme complex in S. cerevisiae.
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PMID:Gene-enzyme relationship in the sulfate assimilation pathway of Saccharomyces cerevisiae. Study of the 3'-phosphoadenylylsulfate reductase structural gene. 220 79

Vitamin K hydroquinone formation in rat liver can be catalyzed by a thiol-dependent quinone reductase activity which shares several characteristics with the vitamin K 2,3-epoxide reductase activity. The possibility that a single enzyme catalyzes both reductions was investigated. Values of Vmax/Km for several different vitamin K analogs were determined and found to be similar for both reductase activities. Several different coumarins were also shown to achieve 50% inhibition at similar concentrations for both enzyme activities. The chloro analog of menaquinone-2 was shown to inhibit both reductases, and the presence of either the quinone or epoxide form of the vitamin protected both activities from inactivation. Thioredoxin was shown to function as a reductant for both reductase activities, although the maximum enzyme activity achieved by this reductant was only half that achieved with dithiothreitol as a reductant. Cofractionation of the two reductase activities on a variety of column matrices was also observed. These data strongly support the hypothesis that one microsomal enzyme is capable of catalyzing both reduction of vitamin K 2,3-epoxide to the quinone, and the quinone to vitamin K hydroquinone.
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PMID:Vitamin K epoxide and quinone reductase activities. Evidence for reduction by a common enzyme. 239 Jan 2

We have previously described a novel protein, derived from the 3B6 EBV B-cell line which apparently displayed IL-1 bioactivity. We report here that the protein previously characterized is not a new species of IL-1. Indeed, we have now been able to clone and express a cDNA which identifies this protein as human thioredoxin, an intracellular dithiol oxydo-reductase enzyme. Thioredoxin however, is not a lymphokine and in particular does not possess IL-1 activity. Our earlier data can be explained in the light of recent findings, reported herein, indicating that IL-1 alpha is produced by the 3B6 line as assessed by antibody inhibition studies and IL-1 alpha mRNA expression. Thus our original protein preparation actually contained traces of IL-1 alpha, which was responsible for the biologic activities and thioredoxin.
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PMID:Identification of interleukin 1 alpha produced by the 3B6 human EBV-B cell line. 254 Dec 84

Thioredoxin, a dithiol polypeptide, has been examined as a potential contributor to the recovery of lens epithelial cells from oxidative insult. It is reported that Escherichia coli thioredoxin can (a) effectively reduce lens-soluble protein disulfide bonds generated by H2O2, (b) restore to its initial activity H2O2-inactivated glyceraldehyde-3-phosphate dehydrogenase, (c) act as an effective source of reducing potential for lens methionine sulfoxide peptide reductase, and (d) act as a free radical quencher based on studies with a stable free radical system generated by ascorbic acid and 2,6-dimethoxy-p-benzoquinone. Thioredoxin is much more effective than dithiothreitol in restoring glyceraldehyde-3-phosphate dehydrogenase activity and as a cofactor for methionine sulfoxide peptide reductase. Upon incubation with epithelial cells, thioredoxin can be observed in the cell using rocket immunoelectrophoresis. These cells recover from H2O2 insult more rapidly than control cell preparations based upon 1) analyses of plasma membrane-related activities: leucine and 86Rb uptake and 2) analyses of parameters primarily related to the internal cell metabolism: ATP concentration and glyceraldehyde-3-phosphate dehydrogenase activity. Analysis of thioredoxin in cell preparations indicates that only about 9% is in the reduced state implying a low effective concentration of the polypeptide. The experiments suggest that low levels of thioredoxin may significantly increase the ability of lens epithelial cells to recover from exposure to H2O2.
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PMID:The effect of H2O2 upon thioredoxin-enriched lens epithelial cells. 283 16

Vitamin K 2,3-epoxide reductase activity from liver microsomes requires only a thiol cofactor, particularly dithiothreitol (DTT). In order to identify a likely physiological cofactor, reduced lipoic acid and reduced thioredoxin were tested as cofactors in beef and rat liver microsomal systems. Reduced lipoic acid is only about one-third as active as DTT in both systems. Thioredoxin, however, is significantly more active than either DTT or reduced lipoic acid in both systems; thioredoxin binds 188 times better than does DTT. The thioredoxin must be in the reduced form since omission of either thioredoxin reductase or NADPH results in complete loss of enzyme activity. The concentration of DTT required to obtain maximal enzyme activity may be as much as 485 times greater than the corresponding concentration of reduced thioredoxin that gives the same enzyme activity.
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PMID:Reduced thioredoxin: a possible physiological cofactor for vitamin K epoxide reductase. Further support for an active site disulfide. 314 Aug 5

Two kinds of enzymes (tentatively designated methyl sulfoxide reductases I and II) responsible for the reduction of the methyl sulfoxide group on various xenobiotics have been purified about 223- and 155-fold, respectively, from rat kidney cytosol. The molecular weight was determined to be 12,000 +/- 1000 for methyl sulfoxide reductase I and 24,000 +/- 1000 for methyl sulfoxide reductase II. Thioredoxin or dithiothreitol is essential in order for the reducing activity to occur. The respective Km values of p-bromophenylmethyl sulfoxide were 2.75 and 1.30 mM for methyl sulfoxide reductases I and II. Replacement of the methyl group on the sulfur atom with a longer alkyl group or phenyl group caused a markedly low or negligible substrate activity.
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PMID:Purification and properties of methyl sulfoxide reductases from rat kidney. 361 43


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