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)

A number of genes under the control of the arylhydrocarbon (Ah) receptor were tested for the effects of glucocorticoids on their expression in cultured primary rat hepatocytes. Treatment of cultured hepatocytes with 1.0 microM dexamethasone potentiated the induction (2- to 3-fold) of cytochrome P4501A1, glutathione S-transferase Ya subunit (GSTYa), and UDP-glucuronosyltransferase gene expression by polycyclic aromatic hydrocarbons (PAH), whereas the glucocorticoid agonist suppressed PAH induction of NAD(P)H:quinone oxidoreductase (QOR) subunit and aldehyde dehydrogenase 3C gene expression by 60-80%. These results were seen at the level of enzyme activity for induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin and at the level of enzyme activity, protein, and specific mRNA for induction by 1,2-benzanthracene. Two of these rat genes, GSTYa and QOR are also induced by electrophilic agents, such as t-butylhydroquinone. In the presence of t-butylhydroquinone, dexamethasone caused a similar level of potentiation of GSTYa subunit expression and suppression of QOR subunit expression as was seen with the PAH, 1,2-benzanthracene. Studies using the glucocorticoid receptor antagonist, RU38486, demonstrated that the modulation of PAH induction by glucocorticoids of cytochrome P4501A1 and QOR activity is apparently dependent on action of the glucocorticoid receptor. These results suggest that the positive and negative changes observed are the result of specific alterations in the rates of transcription of these genes because of the action of the glucocorticoid receptor, thereby affecting regulation of GSTYa and QOR by both Ah receptor-dependent and independent mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Regulation of the Ah gene battery via Ah receptor-dependent and independent processes in cultured adult rat hepatocytes. 758 46

Bovine leukemia virus-transformed lamb embryo fibroblasts (line FLK) possess activity of DT-diaphorase of ca. 260 U/mg protein and similar levels of other NADP(H)-oxidizing enzymes: NADH:oxidase, 359 U/mg; NADPH:oxidase, 43 U/mg; NADH:cytochrome-c reductase, 141 U/mg; NADPH:cytochrome-c reductase, 43 U/mg. In general, the toxicity of aromatic nitrocompounds towards FLK cells increases on increase of single-electron reduction potentials (E1(1)) of nitrocompounds or the log of their reduction rate constants by single-electron-transferring enzymes, microsomal NADPH:cytochrome P-450 reductase (EC 1.6.2.4) and mitochondrial NADH:ubiquinone reductase (EC 1.6.99.3). No correlation between the toxicity and reduction rate of nitrocompounds by rat liver DT-diaphorase (EC 1.6.99.2) was observed. The toxicity is not significantly affected by dicumarol, an inhibitor of DT-diaphorase. Nitrocompounds examined were poor substrates for DT-diaphorase, being 10(4) times less active than menadione. Their poor reactivity is most probably determined by their preferential binding to a NADPH binding site, but not to menadione binding site of diaphorase. These data indicate that at comparable activities of DT-diaphorase and single-electron-transferring NAD(P)H dehydrogenases in the cell, the toxicity of nitrocompounds will be determined mainly by their single-electron reduction reactions.
...
PMID:The toxicity of aromatic nitrocompounds to bovine leukemia virus-transformed fibroblasts: the role of single-electron reduction. 766 3

The cytochrome b subunit of the ubiquinol:cytochrome c oxidoreductase (the bc1 complex) contains two heme prosthetic groups, cytochrome bL and cytochrome bH. In addition, this subunit also provides major elements of the quinol oxidation site (Qo) and a separate quinone reductase site (Qi), which are thought to be located on opposite sides of the membrane. Site-directed mutagenesis has been used to explore the role(s) of specific amino acid residues in this subunit from the photosynthetic bacterium Rhodobacter sphaeroides. Previous work identified five residues, Gly48 (Gly33), Ala52 (Gly37), His217 (His202), Lys251 (Lys228), and Asp252 (Asp229), as being either at or near the quinone reductase site (the residue numbers in parentheses designate the equivalent positions in the yeast mitochondrial enzyme). These residues are predicted to be near the cytoplasmic boundaries of transmembrane helices: helix A (G48, A52), helix D (H217), or helix E (K251, D252). In the current work, the importance of two additional highly conserved residues, which are also predicted to be near the cytoplasmic boundaries of transmembrane helices, is explored by site-directed mutagenesis. R114 (helix B) has been substituted with K, Q, and A, and W129 (helix C) has been changed to A and F. The results suggest that a positively charged residue at position 114 is important. The R114K mutation causes only subtle effects, which appear to be localized to cytochrome bH and the quinone reductase site. In contrast, R114Q is not assembled, and R114A, although partially assembled, is nonfunctional and appears to have a very low amount of cytochrome b associated with the complex. Both mutants at position 129 (W129A and W129F) are able to support the photosynthetic growth of the organism, but show abnormal characteristics. The defects associated with the W129A mutation appear to be primarily associated with the quinone reductase site and cytochrome bH, whereas the W129F mutation appears to result in more global defects that also perturb the cytochrome bL locus. The results are consistent with the placement of residues R114 and W129 near the cytoplasmic side of the membrane, but suggest that these residues are important for the assembly and overall stability of the complex.
...
PMID:Site-directed mutagenesis of arginine-114 and tryptophan-129 in the cytochrome b subunit of the bc1 complex of Rhodobacter sphaeroides: two highly conserved residues predicted to be near the cytoplasmic surface of putative transmembrane helices B and C. 794 7

In this study, Morris hepatoma 7800C1 cells (from rat) were exposed to 500 microM perfluorooctanoic acid (PFOA) in the culture medium for 7 days. This treatment resulted in inductions of catalase, lauroyl-CoA oxidase (which catalyzes the first step in peroxisomal beta-oxidation) and of cytochrome P-450IVA (specialized for omega- and omega-1 hydroxylation of fatty acids). Northern blot analysis revealed that the level of mRNA for peroxisomal fatty acyl-CoA oxidase was enhanced in cells treated with PFOA. Inductions of the enzymes mentioned above are generally connected with peroxisome proliferation in vivo. This work also includes a comparison between the activities of catalase, lauroyl-CoA oxidase, DT-diaphorase and glutathione transferase in rat liver homogenate and 7800C1 cells in order to investigate to what extent this cell line differs from the situation in vivo. The findings suggest that the cells selectively lost most of their peroxisomes during transformation into a cell line and subsequent propagation. The control activities of catalase and lauroyl-CoA oxidase (marker enzymes for peroxisomes) were only about 2% of the corresponding enzyme activities in rat liver. In addition, a morphological study revealed that the frequency of peroxisomes in 7800C1 cells is very low. The control activity of glutathione transferase in 7800C1 cells was 11% of the corresponding activity in rat liver homogenate, whereas the level of DT-diaphorase was virtually the same in 7800C1 cells as in rat liver. Electron microscopic investigation of the control cultures revealed all signs of viable cells, with well-developed cell organelles. Treatment of 7800C1 cells with 500 microM PFOA has little effect on cellular morphology.
...
PMID:Effects of perfluorooctanoic acid--a potent peroxisome proliferator in rat--on Morris hepatoma 7800C1 cells, a rat cell line. 801 82

Biochemical and histochemical studies were conducted in aflatoxin B1-induced liver tumors in adult rainbow trout. Specific activities of the phase I enzymes, ethoxyresorufin-O-deethylase (EROD), microsomal and cytosolic epoxide hydrolase (mEH and cEH), aldehyde dehydrogenase (ALDH) and DT-diaphorase, and the phase II enzymes, gamma-glutamyltransferase (gamma-GT), glutathione transferase (GST) and uridine diphosphoglucuronyl transferase (UDPGT) were measured. Cryostat sections of tumor and surrounding liver from the same cohorts were analyzed immunohistochemically for cytochrome P450IA1 and histochemically for ALDH (benzaldehyde and hexanal), DT-diaphorase, gamma-GT and uridine diphosphoglucuronyl dehydrogenase (UDPGdH). In tumor tissues, the largest biochemical changes were found with benzaldehyde dehydrogenase, where activity increased from undetectable levels to 7.4 nmol/min/mg protein, and gamma-GT, where activity increased 12-fold over controls. Increases in other enzymes ranged from 1.26 to 2.84 times that of control liver, except EROD, which decreased, and cEH and mEH, which were unchanged. Histochemical analyses showed the induction of ALDH, gamma-GT, DT-diaphorase and UDPGdH, and the depression of cytochrome P450IA1 in hepatic neoplasms. In addition, marker enzyme histochemistry of neoplasms revealed heterogeneous populations of hepatocytes and absence of necrotic areas.
...
PMID:Biochemical and histochemical properties of hepatic tumors of rainbow trout, Oncorhynchus mykiss. 809 46

The class-3 aldehyde dehydrogenase that is overexpressed (> 100-fold) in human breast adenocarcinoma MCF-7/0 cells made resistant (> 30-fold as judged by LC90s) to oxazaphosphorines, such as mafosfamide, by growing them in the presence of polycyclic aromatic hydrocarbons, e.g., methylcholanthrene (3 microM for 5 days), was isolated and characterized. Its physical and catalytic properties were identical to those of the prototypical human stomach mucosa cytosolic class-3 aldehyde dehydrogenase, type-1 ALDH-3, except that it catalyzed, though not very rapidly, the oxidation of aldophosphamide, whereas the stomach mucosa enzyme essentially did not; hence, it was judged to be a slight variant of the prototypical enzyme. Carcinogens that are not ligands for the Ah receptor, barbiturates known to induce hepatic cytochrome P450s, steroid hormones, an antiestrogen, and oxazaphosphorines did not induce the enzyme or the largely oxazaphosphorine-specific acquired resistance. Whereas methylcholanthrene induced (a) resistance to mafosfamide and (b) class-3 aldehyde dehydrogenase activity, as well as glutathione S-transferase and DT-diaphorase activities, in the estrogen receptor-positive MCF-7/0 cells, it did not do so in two other human breast adenocarcinoma cell lines, MDA-MB-231 and SK-BR-3, each of which is estrogen receptor negative. Expression of the class-3 aldehyde dehydrogenase and the loss of sensitivity to mafosfamide by polycyclic aromatic hydrocarbon-treated MCF-7/0 cells were transient; each returned to essentially basal levels within 15 days when the polycyclic aromatic hydrocarbon was removed from the culture medium. Insensitivity to the oxazaphosphorines on the part of polycyclic aromatic hydrocarbon-treated MCF-7/0 cells was not observed when exposure to mafosfamide (30 min) was in the presence of benzaldehyde or octanal, each a relatively good substrate for cytosolic class-3 aldehyde dehydrogenases, whereas it was retained when exposure to mafosfamide was in the presence of acetaldehyde, a relatively poor substrate for these enzymes. These observations demonstrate that ligands for the Ah receptor can induce a transient, largely oxazaphosphorine-specific, acquired cellular resistance, and they are consistent with the notion that elevated levels of a cytosolic class-3 aldehyde dehydrogenase nearly identical to the prototypical type-1 class-3 aldehyde dehydrogenase expressed by human stomach mucosa account for the Ah receptor ligand-induced oxazaphosphorine-specific acquired resistance, most probably by catalyzing the detoxification of aldophosphamide.
...
PMID:Identification of a methylcholanthrene-induced aldehyde dehydrogenase in a human breast adenocarcinoma cell line exhibiting oxazaphosphorine-specific acquired resistance. 817 25

Folding models suggest that the highly conserved histidine 217 of the cytochrome b subunit from the cytochrome bc1 complex is close to the quinone reductase (Qi) site. This histidine (bH217) in the cytochrome b polypeptide of the photosynthetic bacterium Rhodobacter capsulatus has been replaced with three other residues, aspartate (D), arginine (R), and leucine (L). bH217D and bH217R are able to grow photoheterotrophically and contain active cytochrome bc1 complexes (60% of wild-type activity), whereas the bH217L mutant is photosynthetically incompetent and contains a cytochrome bc1 complex that has only 10% of the wild-type activity. Single-turnover flash-activated electron transfer experiments show that cytochrome bH is reduced via the Qo site with near native rates in the mutant strains but that electron transfer between cytochrome bH and quinone bound at the Qi site is greatly slowed. These results are consistent with redox midpoint potential (Em) measurements of the cytochrome b subunit hemes and the Qi site quinone. The Em values of cyt bL and bH are approximately the same in the mutants and wild type, although the mutant strains have a larger relative concentration of what may be the high-potential form of cytochrome bH, called cytochrome b150. However, the redox properties of the semiquinone at the Qi site are altered significantly. The Qi site semiquinone stability constant of bH217R is 10 times higher than in the wild type, while in the other two strains (bH217D and bH217L) the stability constant is much lower than in the wild type. Thus H217 appears to have major effects on the redox properties of the quinone bound at the Qi site. These data are incorporated into a suggestion that H217 forms part of the binding pocket of the Qi site in a manner reminiscent of the interaction between quinone bound at the Qb site and H190 of the L subunit of the bacterial photosynthetic reaction center.
...
PMID:Requirement of histidine 217 for ubiquinone reductase activity (Qi site) in the cytochrome bc1 complex. 829

The tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanone (NNK), induces lung tumors in mice, rats, and hamsters. Phenethyl isothiocyanate (PEITC), which occurs as gluconasturtiin in cruciferous vegetables, is a potent inhibitor of NNK-induced carcinogenesis. The present study investigated the enzymatic basis for the bioactivation of NNK and the mechanisms of the inhibition of this process by dietary PEITC in mice. The apparent Km for the formation of keto aldehyde, keto alcohol, and NNK-N-oxide in lung microsomes was 4.9, 2.6, and 1.8 microM and, in liver microsomes, 5.5, 5.1, and 8.8 microM, respectively. Immunoinhibition studies suggested that cytochrome P450s (P450s) 2A1 and 2B1 or related forms are the major enzymes involved in the oxidative metabolism of NNK in mouse lung microsomes. When female A/J mice were fed diets containing 0, 1, or 3 mumol of PEITC/g of diet for 4 wk, the dietary PEITC had no significant effects on the food consumption and body weight of the mice. NNK oxidation in the lung microsomes of mice consuming the 1 or 3 mumol of PEITC/g of diet was decreased by 13 to 27% or 30 to 50%, respectively. In liver microsomes, whose NNK oxidative metabolism rates were about twice those of lung microsomes on a per mg of protein basis, the activities were decreased by 14 to 31% by the 3 mumol of PEITC/g of diet. The apparent Km remained unchanged, and the apparent Vmax decreased in the lung and liver microsomes of PEITC-fed mice, suggesting a noncompetitive nature of the inhibition. When added to the incubation mixture, PEITC decreased NNK metabolism in a concentration-dependent manner and exhibited a competitive inhibition with apparent Ki values of 51 to 93 nM. Dietary PEITC decreased the hepatic P450 content by 25%, but increased (2-fold) the O-dealkylase activities of 7-pentoxyresorufin (indicative of P450 2B1) and 7-ethoxyresorufin (indicative of P450 1A) in the liver microsomes of mice consuming the 3 mumol of PEITC/g of diet. The P450 2B level was increased in liver microsomes but slightly decreased in the lung microsomes. The p450 2E1 level was increased by dietary PEITC by 1.2- and 1.6-fold in the liver and lung microsomes, respectively. The activities of glutathione S-transferase and NAD(P)H-quinone oxidoreductase in liver and lung microsomes were not affected appreciably by the dietary PEITC treatment. The results suggest that chronic consumption of PEITC decreases the rate of metabolic activation of NNK by chemical inactivation and competitive inhibition of the enzyme(s) responsible for NNK oxidation.
...
PMID:Mechanisms of inhibition of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone bioactivation in mouse by dietary phenethyl isothiocyanate. 832 38

The cytochrome b subunit of the bc1 complex contains two heme components, cytochrome bL and cytochrome bH, and is the locus of both a quinol oxidizing site (Qo or Qz) and a quinone reducing site (Qi or Qc). The quinone reductase site has been previously characterized as the site of interaction for a set of inhibitors including antimycin A, diuron, funiculosin, and HQNO. In this paper, four highly conserved residues in the cytochrome b subunit of Rhodobacter sphaeroides (A52, H217, K251, and D252) were targeted for site-directed mutagenesis. These residues were chosen as being likely to be at or near the quinone reductase site, on the basis of known locations of missense mutations in the homologous yeast subunit that confer resistance to Qc-directed inhibitors. The site-directed mutants all exhibit a normal rate of reduction of cytochrome bH, suggesting a fully functional quinol oxidizing site. However, each of the mutants is impaired, to varying degrees, in the rate of reoxidation of cytochrome bH. Two mutants (H217A and D252A) are unable to grow photosynthetically, indicating a severe defect in the bc1 complex. In both cases, the cause of the defect is the lack of reoxidation of cytochrome bH by ubiquinone. This is the first report of mutations that selectively impair the rate of electron transfer from cytochrome bH to the Qc-site. This set of mutations will be useful not only for modeling the structure of the quinone reducing site but also in elucidating the catalytic mechanism of this portion of the Q-cycle.
...
PMID:Characterization of mutations in the cytochrome b subunit of the bc1 complex of Rhodobacter sphaeroides that affect the quinone reductase site (Qc). 838 45

The expression of hepatic cytochrome P4501A1 (P4501A1), glutathione S-transferase Ya subunit (GST), and NAD(P)H:quinone oxidoreductase (QOR) proteins was evaluated in fetal, neonatal, and adolescent rats treated with 3-methylcholanthrene (MC) and the synthetic glucocorticoid dexamethasone (Dex) to elucidate the developmental aspects of glucocorticoid regulation of the induction of drug metabolizing enzymes by polycyclic aromatic hydrocarbons in vivo. These developmental states were chosen to represent either glucocorticoid deplete or replete conditions due to their differences in circulating glucocorticoid levels. Rats were treated with either MC (10 mg/kg body wt) or Dex (10 mg/kg body wt) or a combination of both and sacrificed 24 h later. In neonatal rats, the enzyme activities of P4501A1, GST, and QOR were increased by MC treatment approximately 65-, 1.4-, and 7-fold, respectively. The induction of these enzymes by MC was further potentiated an additional 2-, 1.5-, and 1.4-fold by concomitant Dex treatment. In adolescent male rats, Dex potentiated MC induction of P4501A1 activity (1.7-fold), but repressed MC induction of GST and QOR activities. When the protein contents for the three enzymes were measured by Western blot analyses, a positive correlation was observed with enzyme activities for all conditions except for the adolescent rat, where hepatic protein content of P4501A1 of rats treated with both MC and Dex was not significantly increased above the level seen with 3-methylcholanthrene treatment alone. The levels of specific mRNA and transcriptional activity for cytochrome P4501A1, GST Ya isozyme, and QOR closely paralleled the changes seen in their protein content in the livers of neonatal and adolescent rats. Dexamethasone potentiation of P4501A1 expression at the protein and RNA level were clearly statistically significant in the neonatal rat, but not in the adolescent rat, suggesting that the circulating levels of glucocorticoids are sufficiently low during the neonatal period that the full expression of induction of P4501A1 was not attained in the absence of exogenously administered glucocorticoids. These data also demonstrate that glucocorticoids have differential effects on the induction of GST Ya subunit and QOR protein and RNA in the neonatal and adolescent state, possibly related to circulating levels of glucocorticoids.
...
PMID:Developmental aspects of glucocorticoid regulation of polycyclic aromatic hydrocarbon-inducible enzymes in rat liver. 847 Sep 11


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

---