Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P30044 (antioxidant enzyme)
 8,037 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The flavoprotein thioredoxin reductase catalyzes the reduction of the small redox protein thioredoxin by NADPH. Thioredoxin reductase contains a redox active disulfide and is a member of the pyridine nucleotide-disulfide oxidoreductase family of flavoenzymes that includes lipoamide dehydrogenase, glutathione reductase, trypanothione reductase, mercuric reductase, and NADH peroxidase. The structure of thioredoxin reductase has recently been determined from X-ray crystallographic data. In this paper, we attempt to correlate the structure with a considerable body of mechanistic data and to arrive at a mechanism consistent with both. The path of reducing equivalents in catalysis by glutathione reductase and lipoamide dehydrogenase is clear. To envisage the path of reducing equivalents in catalysis by thioredoxin reductase, a conformational change is required in which the NADPH domain rotates relative to the FAD domain. The rotation moves the nascent dithiol from its observed position adjacent to the re surface of the flavin ring system toward the protein surface for dithiol-disulfide interchange with the protein substrate thioredoxin and moves the nicotinamide ring of NADPH adjacent to the flavin ring for efficient hydride transfer. Reverse rotation allows reduction of the redox active disulfide by the reduced flavin. This requires that the enzyme pass through a ternary complex; the kinetic evidence for such a complex is discussed.
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PMID:Mechanism and structure of thioredoxin reductase from Escherichia coli. 755 16

Human thioredoxin reductase is a dimeric enzyme that catalyzes reduction of the disulfide in oxidized thioredoxin by a mechanism involving transfer of electrons from NADPH via FAD to a redox-active disulfide. 1-Chloro-2,4-dinitrobenzene (DNCB) is an alkylating agent used for depleting intracellular GSH and also showing distinct immunomodulatory properties. We have discovered that low concentrations of DNCB completely inactivated human or bovine thioredoxin reductase, with a second order rate constant in excess of 200 M-1 s-1, which is almost 10,000-fold faster than alkylation of GSH. Total inactivation of 50 nM reduced thioredoxin reductase was obtained by 100 microM DNCB after 5 reductase was obtained by 100 microM DNCB after 5 min of incubation at 20 degrees C also in the presence of 1 mM GSH. The inhibition occurred with enzyme only in the presence of NADPH and persisted after removal of DNCB, suggesting alkylation of the active site nascent thiols as the mechanism of inactivation. Thioredoxin reductase modified by DNCB lacked reducing activity with oxidized thioredoxin, 5,5'-dithiobis-(2-nitrobenzoic acid), or sodium selenite. However, the DNCB-modified enzyme oxidized NADPH at a rate of 4.7 nmol/min/nmol of enzyme in the presence of atmospheric oxygen. This activity was not dependent on the presence of DNCB in solution and constituted a 34-fold increase of the inherent low NADPH oxidase activity of the native enzyme. DNCB is a specific inhibitor of mammalian thioredoxin reductase, which reacted 100-fold faster than glutathione reductase. The inactivation of the disulfide reducing activity of thioredoxin reductase and thioredoxin with a concomitant large increase of the NADPH oxidase activity producing reactive oxygen intermediates may mediate effects of DNCB on cells in vivo.
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PMID:1-Chloro-2,4-dinitrobenzene is an irreversible inhibitor of human thioredoxin reductase. Loss of thioredoxin disulfide reductase activity is accompanied by a large increase in NADPH oxidase activity. 787 79

A 25-kDa antioxidant enzyme that provides protection against oxidation systems capable of generating reactive oxygen and sulfur species has previously been identified. The nature of the oxidant eliminated by, and the physiological source of reducing equivalents for, this enzyme, however, were not known. The 25-kDa enzyme is now shown to be a peroxidase that reduces H2O2 and alkyl hydroperoxides with the use of hydrogens provided by thioredoxin, thioredoxin reductase, and NADPH. This protein is the first peroxidase to be identified that uses thioredoxin as the immediate hydrogen donor and is thus named thioredoxin peroxidase (TPx). TPx exists as a dimer of identical 25-kDa subunits that contain 2 cysteine residues, Cys47 and Cys170. Cys47-SH appears to be the site of oxidation by peroxides, and the oxidized Cys47 probably reacts with Cys170-SH of the other subunit to form an intermolecular disulfide. Mutant TPx proteins lacking either Cys47 or Cys170, therefore, do not exhibit thioredoxin-coupled peroxidase activity. The TPx disulfide is specifically reduced by thioredoxin, but can also be reduced (less effectively) by a small molecular size thiol. The Saccharomyces cerevisiae thioredoxin reductase gene was also cloned and sequenced, and the deduced amino sequence was shown to be 51% identical with that of the Escherichia coli enzyme.
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PMID:Thioredoxin-dependent peroxide reductase from yeast. 796 86

The crystal structures of three forms of Escherichia coli thioredoxin reductase have been refined: the oxidized form of the wild-type enzyme at 2.1 A resolution, a variant containing a cysteine to serine mutation at the active site (Cys138Ser) at 2.0 A resolution, and a complex of this variant with nicotinamide adenine dinucleotide phosphate (NADP+) at 2.3 A resolution. The enzyme mechanism involves the transfer of reducing equivalents from reduced nicotinamide adenine dinucleotide phosphate (NADPH) to a disulfide bond in the enzyme, via a flavin adenine dinucleotide (FAD). Thioredoxin reductase contains FAD and NADPH binding domains that are structurally similar to the corresponding domains of the related enzyme glutathione reductase. The relative orientation of these domains is, however, very different in the two enzymes: when the FAD domains of thioredoxin and glutathione reductases are superimposed, the NADPH domain of one is rotated by 66 degrees with respect to the other. The observed binding mode of NADP+ in thioredoxin reductase is non-productive in that the nicotinamide ring is more than 17 A from the flavin ring system. While in glutathione reductase the redox active disulfide is located in the FAD domain, in thioredoxin reductase it is in the NADPH domain and is part of a four-residue sequence (Cys-Ala-Thr-Cys) that is close in structure to the corresponding region of thioredoxin (Cys-Gly-Pro-Cys), with a root-mean-square deviation of 0.22 A for atoms in the disulfide bonded ring. There are no significant conformational differences between the structure of the wild-type enzyme and that of the Cys138Ser mutant, except that a disulfide bond is not present in the latter. The disulfide bond is positioned productively in this conformation of the enzyme, i.e. it stacks against the flavin ring system in a position that would facilitate its reduction by the flavin. However, the cysteine residues are relatively inaccessible for interaction with the substrate, thioredoxin. These results suggest that thioredoxin reductase must undergo conformational changes during enzyme catalysis. All three structures reported here are for the same conformation of the enzyme and no direct evidence is available as yet for such conformational changes. The simplest possibility is that the NADPH domain rotates between the conformation observed here and an orientation similar to that seen in glutathione reductase. This would alternately place the nicotinamide ring and the disulfide bond near the flavin ring, and expose the cysteine residues for reaction with thioredoxin in the hypothetical conformation.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Crystal structure of Escherichia coli thioredoxin reductase refined at 2 A resolution. Implications for a large conformational change during catalysis. 811 95

The genes encoding thioredoxin reductase (trxB), thioredoxin (trxA), protein PA of glycine reductase (grdA) and the first 23 amino acids of the large subunit of protein PC of glycine reductase (grdC) belonging to the reductive deamination systems present in Eubacterium acidaminophilum were cloned and sequenced. The proteins were products of closely linked genes with 314 codons (thioredoxin reductase), 110 codons (thioredoxin), and 158 codons (protein PA). The protein previously called 'atypically small lipoamide dehydrogenase' or 'electron transferring flavoprotein' could now conclusively be identified as a thioredoxin reductase (subunit mass of 34781 Da) by the alignment with the enzyme of Escherichia coli showing the same typical order of the corresponding domains. The thioredoxin (molecular mass of 11742 Da) deviated considerably from the known consensus sequence, even in the most strongly conserved redox-active segment WCGPC that was now GCVPC. The selenocysteine of protein PA (molecular mass of 16609 Da) was encoded by TGA. The protein was highly similar to those of Clostridium purinolyticum and Clostridium sticklandii involved in glycine reductase. Thioredoxin reductase and thioredoxin of E. acidaminophilum could be successfully expressed in E. coli.
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PMID:Components of glycine reductase from Eubacterium acidaminophilum. Cloning, sequencing and identification of the genes for thioredoxin reductase, thioredoxin and selenoprotein PA. 822 22

Disulfide bonds are rarely found in cytoplasmic proteins. Mutations were selected for in Escherichia coli that allow disulfide bond formation in the cytoplasm. In the presence of these mutations, export-defective versions of alkaline phosphatase and mouse urokinase were able to fold into their enzymatically active conformations in the cytoplasm because their disulfide bonds were formed. The mutations were mapped to the gene for thioredoxin reductase and diminish or eliminate the activity of this enzyme. Thioredoxin itself was found to be unnecessary for this disulfide bond formation. Thioredoxin reductase, but not thioredoxin, is thus implicated in keeping cysteines reduced in cytoplasmic proteins.
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PMID:Mutations that allow disulfide bond formation in the cytoplasm of Escherichia coli. 825 21

Thioredoxin reductase (TR-RED) pertains to the family of pyridine nucleotide disulfide oxidoreductases distinguished by their remarkable structural homology. The enzyme is a constituent component of the thioredoxin complex which is present in all types of organisms and is universal in respect of the numerous physiological functions it performs. The ability of TR-RED to protect the skin from UV-generated free oxygen species has been found. Owing to its ability to control melanin biosynthesis, the enzyme "doses" the suntan.
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PMID:[Thioredoxin-reductase: structure, properties, and function]. 839 72

E. coli thiol peroxidase (Tpx) linked to the thioredoxin as an in vivo thiol regenerating system acts as an antioxidant enzyme removing peroxides and H2O2. In order to elucidate the mechanism regulating tpx gene expression in E. coli in response to oxygen stress, we made 5' progressive deletions of upstream region from tpx gene, and fused to lacZ gene. LacZ activity was increased 6-fold by oxygen stress and inverted repeat sequence located between -47 and -33 nt was proven to be essential for the oxygen response of tpx promoter. Primer extension experiment and analysis of upstream sequence revealed transcription start point, -10, and -35 regions, which are in good agreements with the consensus sequences recognized by E sigma 70. Northern hybridization showed that expression of tpx gene is regulated at the transcriptional level. DNA binding assays using inverted repeat sequence including -35 region provides preliminary evidence that expression of tpx requires additional transcriptional factor in response to oxygen stress.
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PMID:Identification of promoter in the 5'-flanking region of the E. coli thioredoxin-linked thiol peroxidase gene: evidence for the existence of oxygen-related transcriptional regulatory protein. 863 14

The possible relationship of selenium to immunological function which has been suggested for decades was investigated in studies on selenium metabolism in human T cells. One of the major 75Se-labeled selenoproteins detected was purified to homogeneity and shown to be a homodimer of 55-kDa subunits. Each subunit contained about 1 FAD and at least 0.74 Se. This protein proved to be thioredoxin reductase (TR) on the basis of its catalytic activities, cross-reactivity with anti-rat liver TR antibodies, and sequence identities of several tryptic peptides with the published deduced sequence of human placental TR. Physicochemical characteristics of T-cell TR were similar to those of a selenocysteine (Secys)-containing TR recently isolated from human lung adenocarcinoma cells. The sequence of a 12-residue 75Se-labeled tryptic peptide from T-cell TR was identical with a C-terminal-deduced sequence of human placental TR except that Secys was present in the position corresponding to TGA, previously thought to be the termination codon, and this was followed by Gly-499, the actual C-terminal amino acid. The presence of the unusual conserved Cys-Secys-Gly sequence at the C terminus of TR in addition to the redox active cysteines of the Cys-Val-Asn-Val-Gly-Cys motif in the FAD-binding region may account for the peroxidase activity and the relatively low substrate specificity of mammalian TRs. The finding that T-cell TR is a selenoenzyme that contains Se in a conserved C-terminal region provides another example of the role of selenium in a major antioxidant enzyme system (i.e., thioredoxin-thioredoxin reductase), in addition to the well-known glutathione peroxidase enzyme system.
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PMID:Selenocysteine, identified as the penultimate C-terminal residue in human T-cell thioredoxin reductase, corresponds to TGA in the human placental gene. 865 Feb 34

Thioredoxin reductase is a member of the pyridine nucleotide-disulfide oxidoreductase family of enzymes. By delivering reducing equivalents to thioredoxin, thioredoxin reductase exerts control over a number of redox-sensitive factors in the cell, including ribonucleotide reductase and several transcription factors. We have localized the human thioredoxin gene to chromosomal position 12q23-q24.1 by in situ hybridization. We have also determined the relative tissue distribution of thioredoxin reductase mRNA as well as thioredoxin mRNA by probing a Northern blot of several human normal tissues.
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PMID:Human thioredoxin reductase gene localization to chromosomal position 12q23-q24.1 and mRNA distribution in human tissue. 892 4


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