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Results for “Thioredoxin-Disulfide Reductase”

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At least 19 recordsLinked to original sources
PubMed1979

Structure and enzymatic functions of thioredoxin refolded by complementation of two tryptic peptide fragments.

The physicochemical and catalytic properties of thioredoxin-T' are described. This complemented protein structure consists of a 1:1 complex between the inactive fragments thioredoxin-T-(1--73) and thioredoxin T-(74--108). These are generated by selective trypsin cleavage at Arg-73 in lysine-modified and denatured Escherichia coli thioredoxin. Thioredoxin-T' was a slowly formed but stable complex with an apparent KD below 10(-8) M. The tryptophan fluorescence spectrum and the CD spectrum were very similar to those of native thioredoxin; some conformational differences were detected by gel chromatography and radioimmunoassay. Thioredoxin-T'-S2 was a substrate for NADPH and thioredoxin reductase and had 1--2% of the activity of native thioredoxin. This low relative activity was the result of a major increase in the Km value. Thioredoxin-(SH)2 was a hydrogen donor for E. coli ribonucleotide reductase with about 3% relative activity. These results for thioredoxin-T' are correlated with the known three-dimensional structure of thioredoxin. The microenvironment around Arg-73 that is close to the active disulfide appears to be of critical importance for the interactions of thioredoxin with thioredoxin reductase and ribonucleotide reductase.

Amino Acid Sequence↗
PubMed1975

Identification of NADPH-thioredoxin reductase system in Euglena gracillis.

Euglena gracilis contains a protein system which can utilize the reducing power of NADPH in the ribonucleotide reductase-catalyzed reduction of CTP. The proteins required for this reaction are a flavoprotien with a molecular weight of approximately 185,000 which is functionally similar to thioredoxin reductase (NADPH), EC 1.6.4.5, and another protein (Protein I) whose function in the reaction is unknown. This new protein does not appear to contain a prosthetic group and has a molecular weight of approximately 240,000. In addition, the ribonucleotide reductase active in the Euglena NADPH-thioredoxin reductase system is more complex than the protein reported in a previous publication [(1974) j. Biol. Chem. 249, 4428-4434]. The enzyme preparation described in this report contains four different types of polypeptide chains which may complex to form the active enzyme.

Cytosine Nucleotides↗
PubMed1977

Isolation of an Escherichia coli mutant deficient in thioredoxin reductase.

A mutant of Escherichia coli defective in thioredoxin reductase has been isolated and partially characterized. This mutant has no detectable thioredoxin reductase activity in vitro and yet it exhibits no in vivo defect in reduction of ribonucleotides. Evidence is presented that indicates that, in cells permeabilized via ether treatment, ribonucleoside diphosphate reduction can utilize glutathione as an alternate reducing system.

Escherichia coli↗
PubMed1975

Isolation of an Escherichia coli mutant deficient in glutathione synthesis.

A mutant of Escherichia coli that contains essentially no detectable glutathione has been isolated. The mutant contains a very low level of the enzyme glutathione synthetase and accumulates lambda-glutamyl cysteine at a concentration approximately equal to the level of glutathione found in its parent. No significant differences in growth were observed between the mutant and its parent. However, the activity of at least one enzyme was found to be affected by the absence of glutathione; the specific activity of the B1 subunit of ribonucleoside diphosphate reductase was greatly reduced. The possibility that the decreased B1 activity is due to a mutation in the structural gene coding for B1 or its regulatory gene could be eliminated. This suggests that one role of glutathione in the cell is to maintain at least this one protein in an active state. We propose the designation gshB for the gene coding for glutathione synthetase.

Cell-Free System↗
PubMed1977

Purification of thioredoxin, thioredoxin reductase, and glutathione reductase by affinity chromatography.

A scheme is described for the large scale purification of thioredoxin, thioredoxin reductase, and glutathione reductase. The scheme is based on an initial separation of thioredoxin from the two reductases by affinity chromatography on agarose-bound N6-(6-aminohexyl)-adenosine 2',5'-bisphosphate (agarose-2',5'-ADP). The two reductases were then separated by hydrophobic chromatography and purified separately to homogeneity. Thioredoxin was purified to homogeneity by immunoadsorption to agarose containing immobilized goat anti-thioredoxin. Overall yields for thioredoxin, thioredoxin reductase, and glutathione reductase exceeded 80% in each case. Both reductases exhibit an absorption band at approximately 320 nm which appears due to a residual amount of tightly bound NADP. Presence of this absorption band has no apparent effect on the specific activity of either enzyme.

Bacterial Proteins↗
PubMed1977

Purification of thioredoxin reductase from the Novikoff rat tumor.

Thioredoxin reductase (E.C.1.6.4.5.) has been purified to about 95% homogeneity from the Novikoff ascites rat tumor. The enzyme contained two subunits of approximately 58,000 daltons, with one FAD per subunit. The amino acid analysis is reported. An immunoadsorbent was prepared and used for affinity chromatography in order to improve the yield of the enzyme.

Amino Acids↗
PubMed1978

Comparison of thioredoxin reductases from Novikoff ascites hepatoma cells and normal liver of rats.

Adult rat liver contained variant forms of thioredoxin reductase with isoelectric points at pH 4.9 and at approximately pH 4.7 compared to pH 5.1 for the enzyme from Novikoff ascites hepatoma. Fetal and regenerating liver contained only the form with the isoelectric point at pH 4.9. All three enzymes precipitated with and were inhibited by a rabbit antibody to purified enzyme from Novikoff tumor.

Animals↗
PubMed1992

Is thioredoxin the physiological vitamin K epoxide reducing agent?

E. coli thioredoxin plus thioredoxin reductase have previously been shown to replace dithiothreitol as the electron donor for mammalian liver microsomal vitamin K epoxide reduction in vitro. Such activity is dependent on detergent disruption of the microsomal membrane integrity. A previously characterized salicylate-inhibitable pathway for electron transfer from endogenous cytosolic reducing agents to the microsomal epoxide reducing warfarin-inhibitable enzyme is not inhibited by known alternate substrates and inhibitors of the thioredoxin system nor by antibodies against thioredoxin.

Animals↗
PubMed1978

Three-dimensional structure of thioredoxin induced by bacteriophage T4.

The three-dimensional structure of thioredoxin from bacteriophage T4 has been determined from a 2.8-angstrom resolution electron density map. Phase angles for this map were determined from one heavy atom derivative and anomalous differences from cadmium in the native crystals. The molecule of 87 amino acid residues is built up from two simple folding units; a betaalphabeta unit from the amino end of the chain and a betabetaalpha unit from the carboxyl end. This structure is similar to that of thioredoxin from Escherichia coli in spite of their completely different amino acid sequences. The redox-active S--S bridge is part of a protrusion of the molecule as in E. coli thioredoxin, but with quite different surroundings. The structural differences in this region have been correlated to differences in specificity towards the enzyme ribonucleotide reductase from different species.

Amino Acid Sequence↗