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

---

Query: EC:1.6.5.2 (NQO1)
6,196 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Diethyl pyrocarbonate inhibited diaphorase activity of ferredoxin-NADP+ oxidoreductase with a second-order rate constant of 2 mM-1 X min-1 at pH 7.0 and 20 degrees C, showing a concomitant increase in absorbance at 242 nm due to formation of carbethoxyhistidyl derivatives. Activity could be restored by hydroxylamine, and the pH curve of inactivation indicated the involvement of a residue having a pKa of 6.8. Derivatization of tyrosyl residues was also evident, although with no effect on the diaphorase activity. Both NADP+ and NADPH protected the enzyme against inactivation, suggesting that the modification occurred at or near the nucleotide binding domain. The reductase lost all of its diaphorase activity after about two histidine residues had been blocked by the reagent. In differential-labeling experiments with NADP+ as protective agent, it was shown that diaphorase inactivation resulted from blocking of only one histidyl residue per mole of enzyme. Modified reductase did not bind pyridine nucleotides. Modification of the flavoprotein in the presence of NADP+, i.e., with full preservation of diaphorase activity, resulted in a significant impairment of cytochrome c reductase activity, with a second-order rate constant for inactivation of about 0.5 mM-1 X min-1. Reversal by hydroxylamine and spectroscopic data indicated that this second residue was also a histidine. Ferredoxin afforded only slight protection against this inhibition. Conversely, carbethoxylation of the enzyme did not affect complex formation with the ferrosulfoprotein. Redox titration of the modified reductase with NADPH and with reduced ferredoxin suggested that the second histidine might be located in the electron pathway between FAD and ferredoxin.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Essential histidyl residues of ferredoxin-NADP+ oxidoreductase revealed by diethyl pyrocarbonate inactivation. 668 70

Two procedures have been developed for the solubilization of vitamin K epoxide reductase from rat liver microsomal membranes using the detergent Deriphat 160 at pH 10.8. The methods are applicable to both normal and Warfarin-resistant-strain rat liver microsomes and yield material suitable for further purification. The preparations retain dithiothreitol-dependent vitamin K quinone reductase activity as well as vitamin K epoxide reductase and are free of vitamin K-dependent carboxylase and epoxidase activities. Optimal epoxide reductase activity is obtained at 0.1 M KCl and pH 9 in the presence of sodium cholate. Artifactual formation of vitamin K metabolites was eliminated through the use of mercuric chloride to remove excess dithiothreitol prior to extraction and metabolite assay. Using the solubilized enzyme, valid initial velocities were measured, and reproducible kinetic data was obtained. The substrate initial velocity patterns were determined and are consistent with a ping-pong kinetic mechanism. The kinetic parameters obtained are a function of the cholate concentration, but do not vary drastically from those obtained using intact microsomal membranes. At 0.8% cholate, the enzymes solubilized from normal Warfarin-sensitive- and Warfarin-resistant-strain rat livers exhibit respective values of Vmax = 3 and 0.75 nmol/min/g liver; Km for vitamin K epoxide = 9 and 4 microM; and Km for dithiothreitol of 0.6 and 0.16 mM.
...
PMID:Solubilization and characterization of vitamin K epoxide reductase from normal and warfarin-resistant rat liver microsomes. 669 43

Periodate-oxidized NADP+ (dialdehyde-NADP+) inactivated soluble ferredoxin-NADP+ oxidoreductase and combined covalently to the enzyme. This inactivation was first order with respect to dialdehyde-NADP+ and followed saturation kinetics, indicating that the enzyme initially forms a reversible complex with the inactivator. NADP+ afforded complete protection against inactivation, while spinach ferredoxin was uneffective. In the presence of exogenous ferredoxin and illuminated thylakoids, the nucleotide analog functioned as a coenzyme for the reductase, although with rather lower efficiency than NADP+. It also acted as a competitive inhibitor with respect to NADPH in diaphorase activity. Incorporation of radioactivity from periodate-oxidized [3H]NADP+ gave a stoichiometry of 0.85 mol of reagent/mol of reductase, indicating that the modification of a single residue in the flavoprotein is responsible for the loss of enzymatic activity.
...
PMID:Affinity labeling of spinach ferredoxin-NADP+ oxidoreductase with periodate-oxidized NADP+. 670

The NADH-dependent vitamin K-reductase activity of liver microsomes from three closely related rat strains has been studied. One strain (TAS) is susceptible and two strains (HW and HS) resistant to the anticoagulant and lethal effects of warfarin. The effects of cofactors, temperature, detergent and dithiothreitol on vitamin K1 reduction and solvent extraction of substrate and product have been investigated. Vitamin K-reductase activity was inhibited by approximately 13 and 8% respectively when microsomal preparations from TAS and HW animals were incubated with 50 microM vitamin K1 and 10 microM warfarin. In HS rat liver microsomes the enzyme was highly resistant to inhibition by warfarin. Evidence is presented and discussed that suggests that NADH-dependent vitamin K-reductase may be inhibited in the anticoagulant effect of warfarin and may be altered as a result of expression of the warfarin-resistance gene in HS rats. The enzyme activity studied was probably not a DT-diaphorase although both NADH and NADPH acted as cofactors for the reaction.
...
PMID:Inhibition by warfarin of liver microsomal vitamin K-reductase in warfarin-resistant and susceptible rats. 671 38

The water-soluble carbodiimide, N-ethyl-3-(3-dimethylaminopropyl)carbodiimide was found to effectively cross-link ferredoxin to ferredoxin-NADP+ reductase. The covalent complex has a stoichiometry of 1 mol of ferredoxin per mol of the reductase. The flavoprotein moiety of the cross-linked complex maintains most of its diaphorase activity and more interestingly has gained the capacity to catalyze the NADPH-cytochrome c reaction without addition of free ferredoxin in the assay mixture. Furthermore, the cross-linked complex binds NADP+ with a Kd = 88 microM at an ionic strength of 0.02 M. These results show that a ternary complex among the reductase and its substrates can be formed, suggesting that the binding sites for ferredoxin and the pyridine nucleotides are distinct. The bound ferredoxin can interact with cytochrome c; the iron-sulfur cluster of the cross-linked complex is shown to be reduced under anaerobic conditions by NADPH and to be required for the catalysis of the NADPH-cytochrome c reductase reaction. The cross-linked complex, added to thylakoids inhibited by the antibody against the reductase, catalyzes the H2O-cytochrome c photoreduction, which suggests that the ferredoxin moiety of the complex can interact with its electron donor in the photosynthetic chain. Restoration of NADP+ photoreduction requires the addition of free ferredoxin.
...
PMID:A cross-linked complex between ferredoxin and ferredoxin-NADP+ reductase. 672 48

The ferredoxin-NADP+ oxidoreductase of spinach chloroplasts was purified from a Triton X-100 thylakoid extract closely associated with an intrinsic polypeptide of 17.5 kDa. The 17.5-kDa polypeptide-reductase complex differs from soluble ferredoxin-NADP+ reductase in (a) its elution profile in an Affi-Gel blue column; (b) its behavior in isoelectric focusing electrophoresis; and (c) giving different immunoelectrophoretic arcs. The diaphorase activity of the purified complex showed the same pH profile of thylakoid-bound reductase. The curve changed to a form similar to that of soluble reductase after dissociation of the complex. Dissociation allowed separation of the components and was reversible. It is suggested that the 17.5-kDa intrinsic polypeptide is the reductase-binding protein and that it may play an important role in the physiological regulation of the reductase and of photosynthetic electron transport.
...
PMID:Evidence for the existence of a thylakoid intrinsic protein that binds ferredoxin-NADP+ oxidoreductase. 673 31

The dithiothreitol-dependent vitamin K and vitamin K 2,3-epoxide hepatic microsomal reductase activities of warfarin-susceptible and warfarin-resistant rats were compared to gain insight into the role(s) of these activities in vitamin K metabolism and function. In microsomes from resistant rats, 3- to 4-fold more warfarin was required to produce 50% inhibition (I50) of vitamin K reduction to vitamin K hydroquinone than in microsomes from susceptible rats. For the reduction of vitamin K 2,3-epoxide to vitamin K a 6-fold higher warfarin concentration was required. In microsomes from resistant rats, the I50 warfarin concentration required to inhibit gamma-carboxylation of microsomal precursor protein was also 4-fold higher with vitamin K as substrate and was 6-fold higher with the epoxide as substrate than in microsomes from susceptible rats. Collectively, these data suggest that the vitamin K reductase contributes to the metabolism of vitamin K in intact rats and that warfarin inhibition of both the vitamin K and vitamin K 2,3-epoxide reductases is involved in its anticoagulant effect.
...
PMID:Evidence that warfarin anticoagulant action involves two distinct reductase activities. 681 77

The triazine dyes, Cibacron blue F3GA and Procion red HE3B inhibited diaphorase activity of ferredoxin-NADP+ reductase, in a competitive manner with respect to NADPH. The Ki values were 1.5 and 0.2 microM, respectively. Binding of the dyes to the flavoprotein, as measured by difference spectroscopy, indicated an apparent stoichiometry of 1 mol dye/mol reductase and was prevented by NADP+ or high ionic strength. Chemical modification of a lysine residue and a carboxyl group at the NADP(H) binding site of the enzyme prevented complex formation with Procion red. Procion red showed a higher affinity for ferredoxin-NADP+ reductase than Cibacron blue. The Kd values were 1.9 and 5 microM, respectively. Once covalently linked to a Sepharose matrix, the triazine compounds specifically bind the flavoprotein. The interaction is partially electrostatic and partially hydrophobic. The enzyme can be eluted by high concentrations of salt or low concentrations of the corresponding coenzyme. The use of this affinity column allows the rapid purification of ferredoxin-NADP+ oxidoreductase from spinach leaves with good yields.
...
PMID:Interaction of ferredoxin-NADP+ oxidoreductase with triazine dyes. A rapid purification method by affinity chromatography. 682 90

A Japanese family with congenital methaemoglobinaemia is described. The family pedigree was compatible with autosomal recessive type of inheritance. The increased methaemoglobin concentration was ascribed to the red cell NADH diaphorase deficiency associated with the almost complete lack of one of the two peaks of the diaphorase activity as separated by DEAE Sephadex column chromatography. The NADH diaphorase and NADH methaemoglobin reductase deficiency was limited to the red cells. The methaemoglobin content in the blood of the propositus was 17.8% and isoelectric focusing analysis on a polyacrylamide gel plate showed that the haemoglobin consisted of 65.2% oxyhaemoglobin (alpha 2+ beta 2+)2, 29.6% half-oxidized forms, 20.9% (alpha 3+ beta 2+)2 and 8.7% (alpha 2+ beta 3+)2, and 3% full-oxidized methaemoglobin (alpha 3+ beta 3+)2. Oral administration of riboflavin 120 mg/d resulted in a gradual but significant decrease in the level of the met-form haemoglobins in parallel with a gradual increase in the red cell flavin content. Riboflavin is considered to be effective by activating the NADPH diaphorase (NADPH flavin reductase) system and appears to be useful for the treatment of congenital methaemoglobinaemia.
...
PMID:Congenital methaemoglobinaemia due to NADH methaemoglobin reductase deficiency: successful treatment with oral riboflavin. 689 37

The purification and properties of metlegoglobin reductase from lupine (Lupinus luteus L.) nodules are described. The purification procedure results in a 1056-fold purification of the enzyme with a total yield of 21%. The enzyme possesses the NADH-diaphorase activity. Metlegoglobin reductase is heterogenous during electrophoresis and isoelectric focusing. Electrophoresis produces two vicinal active bands, while isoelectrofocusing results in four active fractions. The fraction possessing the highest activity has a pI of 4.4. The enzyme is a flavoprotein, in which all flavins are represented by FAD. The molecular weight of the enzyme is 30 000. In some properties metlegoglobin reductase from lupine nodules is similar to methemoglobin reductase from erythrocytes and metmyoglobin reductase from muscles.
...
PMID:[Properties of metlegoglobin reductase from lupine nodules]. 689 54


<< Previous 1 2 3 4 5 6 7 8 9 10

---