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

Although a sulfate-reducing pathway in Escherichia coli involving free sulfite and sulfide has been suggested, it is shown that, as in Chlorella, a pathway involving bound intermediates is also present. E. coli extracts contained a sulfotransferase that transferred the sulfonyl group from a nucleosidephosphosulfate to an acceptor to form an organic thiosulfate. This enzyme was specific for adenosine 3'-phosphate 5'-phosphosulfate, did not utilize adenine 5'-phosphosulfate, and transferred to a carrier molecule that was identical with thioredoxin in molecular weight and amino acid composition. In the absence of thioredoxin, only very low levels of the transfer of the sulfo group to thiols was observed. As in Chlorella, thiosulfonate reductase activity that reduced glutathione-S-SO3- to bound sulfide could be detected. In E. coli, this enzyme used reduced nicotinamide adenine dinucleotide phosphate and Mg2+, but did not require the addition of ferredoxin or ferredoxin nicotinamide adenine dinucleotide phosphate reductase. Although in Chlorella the thiosulfonate reductase appears to be a different enzyme from the sulfite reductase, the E. coli thiosulfonate reductase and sulfite reductase may be activities of the same enzyme.
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PMID:Sulfate-reducing pathway in Escherichia coli involving bound intermediates. 0 97

Assimilatory sulphate reduction, largely restricted to plants and microorganisms where it provides reduced sulphur for the formation of amino acids and proteins, nucleic acids, and various sulphur-containing coenzymes, begins with the activation of sulphate through reaction with ATP to form adenosine 5'-phosphosulphate (APS) and adenosine 3'-phosphate 5'-phosphosulphate (PAPS). Two pathways of assimilatory sulphate reduction are known. One, found in some blue-green algae (cyanobacteria) and in all oxygen-envolving eukaryotes, begins with APS where the sulpho group is transferred via APS sulphotransferase to a thiol acceptor (glutathione (G-S-) in Chlorella) to form the organic thiosulphate (G-S-SO-3). The organic thiosulphate appears to be reduced further by an organic thiosulphate reductase employing reduced ferredoxin to form G-S-S-. The terminal sulphur is then thought to be reductively transferred to O-acetylserine via O-acetylserine sulphydrase to form cysteine. A second pathway, found in bacteria and fungi, begins with PAPS where the sulpho group is transferred via PAPS sulphotransferase to an acceptor thiol to form an organic thiosulphate. Since thioredoxin is indispensable, this molecule may be the carrier or may serve to reduce the carrier. NADPH via thioredoxin reductase or glutathione and glutathione reductase reduces thioredoxin. These reactions release sulphite which is further reduced to sulphide by sulphite reductase, employing NADPH. Sulphide is then thought to react with O-acetylserine to form cysteine via O-acetylserine sulphydrase. The cellular location and evolution of these pathways is discussed.
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PMID:Pathways of assimilatory sulphate reduction in plants and microorganisms. 39 67

The biological pathways of ribonucleotide reduction are briefly reviewed. The hypothesis is presented that reduction of ribonucleoside triphosphates to their deoxynucleotide analogs through the mediation of vitamin B12 or a similar corrinoid preceded and was necessary for the subsequent development of a DNA-type genome. There are two known biological systems for ribonucleotide reduction: (1) The ribonucleoside diphosphate reduction system which utilizes a nonheme iron ribonucleotide reductase enzyme, thioredoxin and its reductase, and NADPH. This enzyme complex is found in most bacteria, some higher organisms, and in all animals. (2) The ribonucleoside triphosphate reduction system which utilizes adenosyl cobalamin, ribonucleotide reductase and either thioredoxin or a disulfhydryl compound. The cobalamin-dependent reductase is restricted to a few species of bacteria and blue-gree algae. This system is considered more primitive than the iron reductase one based on their differences in distribution, components, and products.
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PMID:Ribonucleotide reduction and the possible role of cobalamin in evolution. 59 75

The thioredoxin system, comprising NADPH, thioredoxin reductase and thioredoxin reduces protein disulfides via redox-active dithiols. We have discovered that sodium selenite is a substrate for the thioredoxin system; 10 microM selenite plus 0.05 microM calf thymus thioredoxin reductase at pH 7.5 caused a non-stoichiometric oxidation of NADPH (100 microM after 30 min). In contrast, thioredoxin reductase from Escherichia coli showed no direct reaction with selenite, but addition of 3 microM E. coli thioredoxin also resulted in non-stoichiometric oxidation of NADPH, consistent with oxidation of the two active-site thiol groups in thioredoxin to a disulfide. Kinetically, the reaction was complex with a lag phase at low selenite concentrations. Under anaerobic conditions the reaction stopped after 1 mol selenite had oxidized 3 mol NADPH; the admission of air then resulted in continued consumption of NADPH consistent with autooxidation of selenium intermediate(s). Ferricytochrome c was effectively reduced by calf thymus thioredoxin reductase and selenite in the presence of oxygen. Selenite caused a strong dose-dependent inhibition of the formation of thiol groups from insulin disulfides with either the E. coli or calf-thymus thioredoxin system. Thus, under aerobic conditions selenite catalyzed, NADPH-dependent redox cycling with oxygen, a large oxygen-dependent consumption of NADPH and oxidation of reduced thioredoxin inhibiting its disulfide-reductase activity.
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PMID:Selenite is a substrate for calf thymus thioredoxin reductase and thioredoxin and elicits a large non-stoichiometric oxidation of NADPH in the presence of oxygen. 132 13

The arsenic resistance operon of Staphylococcus aureus plasmid pI258 consists of three genes, arsR (encoding the repressor regulatory protein), arsB (the determinant of the membrane efflux protein that confers resistance by pumping arsenic from the cells), and arsC (the small gene whose protein product is required for arsenate resistance only, not for arsenite resistance). ArsC has now been shown to be an arsenate reductase, converting intracellular arsenate [As(V)] to arsenite [As(III)], which is then exported from the cells by an energy-dependent efflux process. The arsenate reductase activity was found in the soluble cytoplasmic fraction in Escherichia coli (and not associated with the periplasmic fraction or the sedimentable cell envelope). Purified ArsC protein coupled in vitro with thioredoxin plus dithiothreitol (but not 2-mercaptoethanol or reduced glutathione) to reduce arsenate to arsenite.
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PMID:Reduction of arsenate to arsenite by the ArsC protein of the arsenic resistance operon of Staphylococcus aureus plasmid pI258. 140 57

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

The structural gene encoding a thioredoxin-dependent 5'-phosphoadenylyl sulphate (PAPS) reductase (EC 1.8.4.-) from cyanobacterium Synechococcus PCC 7942 ('Anacystis nidulans') was detected by heterologous hybridization with the cysH gene from Escherichia coli K12. The cyanobacterial gene (further called par gene) comprised 696 nt which are 57.8% homologous to the enterobacterial gene. The putative open reading frame encoded a polypeptide consisting of 232 amino acid residues (deduced molecular weight 26,635) which showed significant homologies to the polypeptide from E. coli (50.8%) and to the polypeptide from Saccharomyces cerevisiae (30.3%). A single cysteine located at the C-terminus of the polypeptide of E. coli (Cys239) was conserved in Synechococcus. Conservation of this cysteinyl residue seems indispensable for catalysis. Complementation of a cysH-deficient mutant of E. coli by the cyanobacterial gene indicated that the cloned DNA is the structural gene of the PAPS reductase.
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PMID:Primary structure of the Synechococcus PCC 7942 PAPS reductase gene. 146 52

It has been shown previously that the thioredoxin system (thioredoxin + thioredoxin reductase + NADPH) may replace dithiothreitol (DTT) as a cofactor for vitamin KO and K reductase in salt-washed detergent-solubilized bovine liver microsomes. Here we demonstrate that the system can be improved further by adding protein disulphide-isomerase (PDI) to the components mentioned above. Moreover, NADPH may be replaced by reduced RNAase as a hydrogen donor. In our in vitro system the various protein cofactors were required at concentrations 2-5 orders of magnitude lower than that of DDT, whereas the maximal reaction rate was about 3-fold higher. PDI stimulated the thioredoxin-driven reaction about 10-fold, with an apparent Km value of 8 microM. These data suggest that in the vitro system the formation of disulphide bonds is somehow linked to the vitamin K-dependent carboxylation of glutamate residues. In vivo, both disulphide formation and vitamin K-dependent carboxylation are post-translational modifications taking place at the luminal side of the endoplasmic reticulum of mammalian secretory cells. The possibility that the reactions are also coupled in vivo is discussed.
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PMID:Stimulation of the dithiol-dependent reductases in the vitamin K cycle by the thioredoxin system. Strong synergistic effects with protein disulphide-isomerase. 173 62

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

The nucleotide sequence of the gene cysH from Escherichia coli K12 was determined. The open reading frame was 735 nucleotides in length; it was flanked by a repetitive palindromic sequence centred 36 nucleotides upstream of cysH and a terminator-like structure located 20 nucleotides downstream. CysH encoded a polypeptide of Mr 27927 consisting of 244 amino acids. The gene product was isolated as a homodimer exhibiting phospho-adenylylsulphate reductase (PAPS reductase) activity. The active enzyme was devoid of electron transferring cofactors and contained only one cysteine per subunit. Reduction of the enzyme by dithiols resulted in a shift of the apparent molecular weight from 44,000 to 62,000 without formation of an enzyme-thioredoxin complex.
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PMID:Characterisation of the gene cysH and of its product phospho-adenylylsulphate reductase from Escherichia coli. 200 73


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