Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.8.1.4 (diaphorase)
2,754 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The system involved in the reduction of 2-[4'-di(2''-bromopropyl) aminophenylazolbenzoic acid (CB10-252), an agent designed for treating primary liver cell cancer, has been demonstrated to be localised mainly in the 108 000 X g supernatant fraction of rat liver homogenate. It is also present in other organs particularly in the spleen. DAB-azoreductase as shown previously is present almost entirely in the microsomal fraction and is found in high concentration only in liver. The pH maximum for CB10-252-azoreductase implying the importance of the 2'-carboxyl group in determining substrate specificity. The use of enzyme inhibitors and other additives showed that CB10-252 WAS NOT AXANTHINE OXIDASE OR DIHYDROFOLATE REDUCTASE. Its activity was not affected by carbon monoxide, phenobarbitone (PB), or 3-methylcholanthrene (MC) pretreatment. Enhancement of the activity by ferrous ions and FAD indicated that at least part of the reduction system could involve a flavoprotein with FAD as the prosthetic group. The activity of CB10-252-azoreductase and methylred-azoreductase was reduced by menadione (vitamin K3), cyanide and propylgallate. A diaphorase preparation from pig heart reduced both CB10-252 and methylred with both NADPH- and NADH-generating systems.
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PMID:Some characteristics of two azoreductase systems in rat liver. Relevance to the activity of 2-[4'-di(2"-bromopropyl)-aminophenylazo]benzoic acid (CB10-252), a compound possessing latent cytotoxic activity. 0 Jan 49

Glutathione reductase (NAD(P)H: oxidized-glutathione oxidoreductase, EC 1.6.4.2) was purified to homogeneity from porcine erythrocytes by use of affinity chromatography on 2',5'-ADP-Sepharose 4-B. Analytical ultracentrifugation experiments were analysed to give the following physical parameters for the enzyme: s20,w = 5.7 S, D20,w = 50 microgram2/s, and Mw = 103 000 (protein concentration, 0.5 mg/ml). The frictional ratio was 1.37 and the Stokes radius was 4.3 nm. The enzyme molecule is a dimer composed of subunits of equal size each containing a FAD molecule. The amino acid compositions and circular dichroism spectra of the porcine and human enzymes indicated extensive structural similarities. The isoelectric point was at pH 6.85 (at 4 degrees C). The absorption spectrum of the oxidized enzyme had maxima at 377 and 462 nm. In vivo the enzyme appears to be partially reduced. At a physiological concentration of reduced glutathione the apparent Michaelis constants for glutathione disulfide and NADPH were higher than in the absence of reduced glutathione. At 0.15 M ionic strength the catalytic activity obtained with NADPH as reductant was optimal at pH 7 and more than 200 times higher than that obtained with NADH. S-sulfoglutathione and some mixed disulfides of glutathione were poor substrates with the exception of the mixed disulfide of coenzyme A and reduced glutathione. The purified enzyme displayed low transhydrogenase activity with oxidized pyridine nucleotide analogs and diaphorase activity with 2,6-dichlorophenolindophenol as acceptor substrates; both NADPH and NADH served as donors.
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PMID:Characterization of glutathione reductase from porcine erythrocytes. 3 12

Results are presented which demonstrate that the 2-electron-reduced lipoamide dehydrogenase (EC 1.6.4.3) from Escherichia coli is a mixture of species. In catalysis, this enzyme cycles between the oxidized and the 2-electron-reduced forms. Three spectrally distinct species are indicated in the pH range 5.8 to 8.0 from measurements of the fluorescence and visible spectra during dithionite titration. These have the following properties. 1) A fluorescent form where the FAD is oxidized and the active center disulfide is reduced. This species is unable to charge transfer and predominates at low pH. 2) A form in which there is a facile charge transfer between thiolate and FAD (epsilon530 - 3300 M-1 cm-1). This species, which predominates at high pH, is very similar to the 2-electron-reduced pig heart enzyme at high pH. 3) A form where the flavin is reduced and the disulfide is oxidized. The spectra of these three species have been determined. Anaerobic reduction of the enzyme with stoichiometric dihydrolipoamide leads to the formation of the charge transfer species in less than 1 s. Subsequently, in a process requiring about 12 s, the charge transfer complex relaxes to a mixture of species observed in dithionite titrations. The pH dependence of the oxidation-reduction potential, the fluorescence, the charge transfer absorbance (530 nm), and the 455 nm absorbance indicates the presence of a base which is able to stabilize the thiolate anion generated upon reduction of the active center disulfide. The pH dependence of the oxidation-reduction potential indicates that the reduction of the enzyme by dihydrolipoamide involves 2 protons as well as 2 electrons. These potentials are somewhat more positive than those determined for the pig heart enzyme and thus explain the ready further reduction of the E. coli enzyme to the 4-electron-reduced enzyme. The pH-independent formation constant (Kf) for the disproportionation of 2-electron-reduced enzyme (2EH2 in equilibrium E + EH4) is about 55 as calculated from dithionite titrations. Therefore at equilibrium there is about 80% 2-electron-reduced enzyme, 1-% oxidized enzyme, and 10% 4-electron-reduced enzyme. The spectrum of fully formed 2-electron-reduced enzyme has been calculated at several pH values from these data. The results confirm the previous conclusion that lipoamide dehydrogenase from E. coli is qualitatively similar to the pig heart enzyme, differing only in certain quantitative features such as the distribution between the various forms at the 2-electron-reduced level.
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PMID:Evidence for multiple electronic forms of two-electron-reduced lipoamide dehydrogenase from Escherichia coli. 3 77

Labelling studies with N-ETHYLMALEIMIDE SHOW THAT EITHER IN THE PRESENCE OF Mg2+, thiamine pyrophosphate (TPP) and pyruvate or in the presence of NADH the overall activity of the pyruvate dehydrogenase complex from Azotobacter vinelandii is inhibited without much inhibition of the partial reactions. The complex undergoes a conformational change upon incubation with NADH. The inhibition by bromopyruvate is less specific. Specific incorporation of a fluorescent maleimide derivative was observed on the two transacetylase isoenzymes. Binding studies with a similar spin label analogue show that 3 molecules/FAD are incorporated by incubation of pyruvate, Mg2+ and TPP, whereas 2 molecules/FAD are incorporated via incubation with NADH. The spin label spectra support the idea that in the complex the active centres of the component enzymes are connected by rapid rotation of the lipoyl moiety. Three acetyl groups are incorporated in the complex by incubation with [2-14C]pyruvate. Time-dependent incorporation supports the view that the two transacetylase isoenzymes react in non-identical ways with the pyruvate dehydrogenase components of the complex. The results show that the complex contains 2 low-molecular-weight transacetylase molecules and 4 molecules of the high-molecular-weight isoenzyme. Mn2+-binding studies show that the complex binds 10 ions, with different affinities. 2 Mn2+ ions are bound with a 20-fold higher affinity than the remaining 8 Mn2+ ions. The latter 8 ions bind with equal affinities and are thought to reflect binding to the pyruvate dehydrogenase components of the complex. It is concluded that the complex contains 8 pyruvate dehydrogenase molecules, 4 high-molecular-weight transacetylase molecules, 2 low-molecular-weight transacetylase molecules and 1 dimeric (2-FAD-containing) symmetric molecule of lipoamide dehydrogenase. Evidence comes from pyruvate-dependent inactivation and labelling studies that the pyruvate dehydrogenase components contain either an - SH group or an S-S bridge which participates in the hydroxyethyl transfer to the transacetylase components.
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PMID:The pyruvate-dehydrogenase complex from Azotobacter vinelandii. 3. Stoichiometry and function of the individual components. 17 36

Asparagusate dehydrogenases I and II and lipoyl dehydrogenase have been obtained in homogeneous state from asparagus mitochondria. They are flavin enzymes with 1 mol of FAD/mol of protein. Asparagusate dehydrogenases I and II and lipoyl dehydrogenase have s20,w of 6.22 S, 6.39 S, and 5.91 S, respectively, and molecular weights of 111,000, 110,000, and 95,000 (sedimentation equilibrium) or 112,000, 112,000, and 92,000 (gel filtration). They are slightly acidic proteins with isoelectric points of 6.75, 5.75, and 6.80. Both asparagusate dehydrogenases catalyzed the reaction Asg(SH)2 + NAD+ equilibrium AsgS2 + NADH + H+ and exhibit lipoyl dehydrogenase and diaphorase activities. Lipoyl dehydrogenase is specific for lipoate and has no asparagusate dehydrogenase activity. NADP cannot replace NAD in any case. Optimum pH for substrate reduction of the three enzymes are near 5.9. Asparagusate dehydrogenases I and II have Km values of 21.5 mM and 20.0 mM for asparagusate and 3.0 mM and 3.3 mM for lipoate, respectively. Lipoyl dehydrogenase activity of asparagusate dehydrogenases is enhanced by NAD and surfactants such as lecithin and Tween 80, but asparagusate dehydrogenase activity is not enhanced. Asparagusate dehydrogenases are strongly inhibited by mercuric ion, p-chloromercuribenzoic acid, and N-ethylmaleimide. Amino acid composition of the three enzymes is presented and discussed.
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PMID:Asparagusate dehydrogenases and lipoyl dehydrogenase from asparagus mitochondria. Physical, chemical, and enzymatic properties. 18 3

The soluble hydrogenase (hydrogen: NAD+ oxidoreductase, EC 1.12.1.2) from Alcaligenes eutrophus H 16 was purified 68-fold with a yield of 20% and a final specific activity (NAD reduction) of about 54 mumol H2 oxidized/min per mg protein. The enzyme was shown to be homogenous by polyacrylamide gel electrophoresis. Its molecular weight and isoelectric point were determined to be 205 000 and 4.85 respectively. The oxidized hydrogenase, as purified under aerobic conditions, was of high stability but not reactive. Reductive activation of the enzyme by H2, in the presence of catalytic amounts of NADH, or by reducing agents caused the hydrogenase to become unstable. The purified enzyme, in its active state, was able to reduce NAD, FMN, FAD, menaquinone, ubiquinone, cytochrome c, methylene blue, methyl viologen, benzyl viologen, phenazine methosulfate, janus green, 2,6-dichlorophenoloindophenol, ferricyanide and even oxygen. In addition to hydrogenase activitiy, the enzyme exhibited also diaphorase and NAD(P)H oxidase activity. The reversibility of hydrogenase function (i.e. H2 evolution from NADH, methyl viologen and benzyl viologen) was demonstrated. With respect to H2 as substrate, hydrogenase showed negative cooperativity; the Hill coefficient was n = 0.4. The apparent Km value for H2 was found to be 0.037 mM. The absorption spectrum of hydrogenase was typical for non-heme iron proteins, showing maxima (shoulders) at 380 and 420 nm. A flavin component could be extracted from native hydrogenase characterized by its absorption bands at 375 and 447 nm and a strong fluorescense at 526 nm.
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PMID:Purification and properties of soluble hydrogenase from Alcaligenes eutrophus H 16. 18 26

A derivative of the flavoprotein pig heart lipoamide dehydrogenase has been described recently (Thorpe, C., and Williams, C.H. (1976) J. Biol. Chem. 251, 3553-3557), in which 1 of the 2 cysteine residues generated on reduction of the intrachain active center disulfide bridge is selectively alkylated with iodoacetamide. This monolabeled enzyme exhibits a spectrum of oxidized bound flavin. The addition of 1 mM NAD+ to this derivative at pH 8.3 causes a decrease in absorbance of approximately 50% at 448 nm, with a concomitant increase at 380 nm. These spectral changes are complete within 3 ms and are reversible. NAD+ titrations generate isosbestic points at 408, 374, and 327 nm; allowing values for the apparent dissociation constant for NAD+ and the extent of bleaching at infinite ligand to be obtained from double reciprocal plots. Between pH 6.1 and 8.8, the apparent KD decreases from 320 to 35 muM, whereas the extrapolated delta epsilon 448 values remain approximately constant at 1/2 epsilon 448. Direct measurement of NAD+ binding by gel filtration at pH 8.8 indicates that the spectral changes are associated with a stoichiometry of 1.2 mol of NAD+ bound/2 mol of FAD. The modified protein is a dimer containing 1 FAD and 1 alkylated cysteine residue/subunit; the native enzyme is also dimeric. The visible spectrum of the species absorbing at 380 nm, approximated by correction for the residual oxidized FAD, shows a single maximum at 384 nm, epsilon 384 = 8.7 mM-1cm-1. Comparison of this spectrum with that of model compounds of known structure suggests that it may represent a reversible covalent flavin adduct induced on binding NAD+.
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PMID:Spectral evidence for a flavin adduct in a monoalkylated derivative of pig heart lipoamide dehydrogenase. 18 94

Fluorescence energy transfer has been employed to estimate the minimum distance between each of the active sites of the 4 component enzymes of the pyruvate dehydrogenase multienzyme complex from Azotobacter vinelandii. No energy transfer was seen between thiochrome diphosphate, bound to the pyruvate decarboxylase active site, and the FAD of the lipoamide dehydrogenase active site. Likewise, several fluorescent sulfhydryl labels, which were specifically bound to the lipoyl moiety of lipoyl transacetylase, showed no energy transfer to either the flavin or thiochrome diphosphate. These observations suggest that all the active centers of the complex are quite far apart (greater than or equal to 40 nm), at least during some stages of catalysis. These results do not preclude the possibility that the distances change during catalysis. Several of the fluorescent probes used possessed multiple fluorescent lifetimes, as shown by determination of lifetime averages by both phase and modulation measurements on a phase fluorimeter. These lifetimes are shown to result from multiple factors, not necessarily related to multiple protein conformations.
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PMID:Fluorescence energy-transfer studies on the pyruvate dehydrogenase complex isolated from Azotobacter vinelandii. 34 64

The dynamic structures of two major forms (LD(I) and LD(II) of pig heart lipoamide dehydrogenase, resolved by TEAE-cellulose column chromatography, were studied by fluorescence depolarization. FAD and ANM were used as an intrinsic and an extrinsic fluorescent probe, respectively. In the experiments with bound FAD of lipoamide dehydrogenase, no thermal dependence of the fluorescence depolarization of either enzyme was observed and the values of polarization were close to the theoretical maximum value of 0.5. Both enzymes contained two reactive thiol groups which differed in their reactivities toward ANM. When the enzymes were labeled with one mol of ANM per mol of enzyme, the rotational relaxation times of LD(I) and LD(II) were found to be 18 ns and 196 ns, respectively. These findings indicate that the sement of LD(I) labeled with ANM fluctuates in the order of nanoseconds, whereas this segment of LD(II) is fixed rigidly. On the other hand, when the enzymes were labeled with two mol of ANM per mol of enzyme, both enzymes showed the composite result of fluorescence depolarization due to the motilities of the segment of enzyme and the whole enzyme molecule. These findings indicate that both LD(I) and LD(II) have the non-equivalent motilities of segments containing one reactive thiol group between the two monomers. In other words, the segment containing the ANM binding site of the one monomer is flexible and this segment of the other monomer is fixed rigidly in both enzymes.
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PMID:Fluorescence studies on lipoamide dehydrogenases of pig heart. I. Conformational dynamics of enzyme. 50 May 85

Spinach nitrate reductase complex previously inactivated by treatment with mercurials p-hydroxymercuribenzoate or p-hydroxymercuriphenyl sulphonate can be reactivated by incubation with dithioerythritol. The reactivation of NADH-diaphorase seems to be FAD-dependent, whereas that of FNH2-nitrate reductase is not. The requirement of FAD for NADH-inactivation of nitrate reductase treated with p-hydroxymercuribenzoate disappears after treatment with dithioerythritol.
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PMID:Nitrate reductase from Spinacea oleracea. FAD and the reactivation of the enzyme treated with p-Hydroxymercuribenzoate. 59 86


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