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:1.6.99.1 (NADPH-diaphorase)
3,903 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Evidence is established for the existence of alternative metabolic routes of N-oxidation of NN-dimethylaniline in rabbit liver microsomal fraction. One pathway involves the participation of two types of cytochrome P-450 with different sensitivities towards heat. Both types may represent distinct haemoprotein species or two physical forms of a single pigment. The other pathway is represented by the mixed-function amine oxidase. The enzyme lacks NADPH dehydrogenase activity and is insensitive to treatment with 2-bromo-4'-nitroacetophenone and steapsin: it catalyses N-oxidation of imipramine, trimethylamine and NN-dimethylaniline in molar proportions considerably different from those of the cytochrome P-450-supported reactions. Cytochrome P-450 is estimated to account for the formation of at least 50-60% of the total NN-dimethylaniline N-oxide formed in the intact rabbit liver microsomal fraction, the remainder arising from the action of the mixed-function amine oxidase.
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PMID:Studies on the mechanism of hepatic microsomal N-oxide formation. The role of cytochrome P-450 and mixed-function amine oxidase in the N-oxidation of NN-dimethylaniline. 40 3

Specimens of the seawater fish annular seabream (Diplodus annularis) were caught from a polluted harbor area and from a clean reference area. Seawater concentrates and fish-muscle extracts were not mutagenic in the Salmonella reversion test. Liver preparations of fish from the 2 sources were comparatively assayed for microsomal mixed-function oxidases and cytosolic biochemical parameters, as well as for the ability of S12 fractions to activate promutagens or to detoxify direct-acting mutagens. A shift of the cytochrome P-450 peak from 450.3 to 448.5 was accompanied by a 4.5-fold increase in arylhydrocarbon hydroxylase activity in fish living in the polluted environment. At the same time, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were doubled in the cytosol of the same animals, while reduced glutathione (GSH) peroxidase and GSH S-transferase were slightly yet significantly depressed. No significant difference was recorded for other biochemical parameters, including GSH, oxidized glutathione (GSSG) reductase, NADH- and NADPH-dependent diaphorases, and DT diaphorase. In parallel, fish exposed to polluted seawater exhibited a significant and marked enhancement of the metabolic activation of the pyrolysis product Trp-P-2 and of benzo[a]pyrene-trans-7,8-diol, and at the same time were less efficient in detoxifying the antitumor compound ICR 191. Liver S12 fractions from both sources efficiently decreased the direct mutagenicity of sodium dichromate, and failed to activate benzo[a]pyrene and aflatoxin B1 to mutagenic metabolites. These results provide evidence that both biochemical parameters and the overall capacity of fish liver to activate or detoxify certain mutagens can be assumed to be sensitive indicators of exposure to mixed organic pollutants in the marine environment.
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PMID:Enhanced liver metabolism of mutagens and carcinogens in fish living in polluted seawater. 170 59

The metabolism of chemical carcinogens was investigated in liver preparations from 28 captive woodchucks (Marmota monax). Of these, 23 were naturally infected with the woodchuck hepatitis virus (WHV), and eight also had primary hepatocellular carcinoma (PHC). Twenty-nine parameters were investigated in liver subcellular fractions, including cross-reactivity with HBsAg, and biochemical parameters, such as gamma-glutamyl transpeptidase, cytochrome P-450 and microsomal monooxygenases (aryl hydrocarbon hydroxylase, ethoxycoumarin and ethoxyresorufin deethylases, aminopyrine and dimethylnitrosamine demethylases, and testosterone 7 alpha-, 16 alpha- and 6 beta-hydroxylases), uridine 5'-diphosphoglucuronosyl transferase, GSH and related enzymes (peroxidase, reductase and S-transferase), as well as other cytosolic enzyme activities (glucose 6-phosphate and 6-phosphogluconate dehydrogenases, NADPH- and NADH-dependent diaphorases, and DT diaphorase). In addition, liver preparations were used in order to quantify the metabolic activation into bacterial mutagens of five procarcinogens (aflatoxin B1, the pyrolysis products Trp-P-2 and MeIQ, 2-aminofluorene and dimethylnitrosamine) and the decrease of potency of three direct-acting mutagens (sodium dichromate, ICR 191 and 4-nitroquinoline 1-oxide). WHV infection produced a significant stimulation of carcinogen metabolism, as shown by the simultaneous change in detoxification parameters (GSH depletion) and activation indices (enhancement of microsomal monooxygenases and of procarcinogen activation into mutagenic metabolites). There were no significant differences between WHV-positive samples from animals without PHC and the noncancerous tissue of PHC-bearing animals, whereas a decrease of both activation and detoxification indices was recorded in the tumorous tissue. There was a considerable interindividual variability among WHV carriers, which was tentatively ascribed to genetic factors. Pregnancy was the only known factor influencing the results in WHV carriers. However, even by excluding pregnant animals, the effects on carcinogen metabolism produced by WHV infection were still statistically significant. These results, together with previous data obtained in humans, revealed that metabolic factors may play a role in the synergism between viral hepatitis and chemical hepatocarcinogens in the etiopathogenesis of PHC.
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PMID:Enhanced metabolic activation of chemical hepatocarcinogens in woodchucks infected with hepatitis B virus. 272 Sep 3

In toxicology, it is of interest not only to assess enzyme levels and capacities for potential fluxes, but it is also useful to develop methods for determining actual concentrations and fluxes in the intact cell and organ. To this end, several noninvasive techniques have been developed over the years. Our interest has been largely in photometric techniques. Transmission spectrophotometry through solid organs permits monitoring of the cytochromes of the mitochondrial respiratory chain and cytochrome P-450 as well as other pigments of biological interest. Furthermore, the steady state level of catalase Compound I in liver provides information on rates of H2O2 production. These are in the nM to microM concentration range. More recently, the monitoring of photoemission from intact organs has been useful in toxicological problems. The major photoemissive species, singlet molecular oxygen and excited carbonyls, can now be monitored with good signal/noise ratio. Redox cycling of quinones and the generation of photoemissive species were studied in menadione metabolism. Inhibition of phase II led to a significant increase in the steady state level of singlet oxygen, as did the inhibition of two-electron reduction by using the inhibitor dicoumarol for DT diaphorase. Conversely, the induction of DT diaphorase by pretreatment with BHA protected by decreasing the level of reactive oxygen species.
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PMID:Intact organ spectrophotometry and single-photon counting. 330 3

1. The chemical reactivity of bromobenzene metabolite(s) responsible for its protein covalent binding was investigated by determining the effects of many chemical and enzymic probes on the metabolism and covalent binding of [3,5-3H]bromobenzene with rat liver microsomes in vitro. 2. Classical cytochrome P-450 enzyme inhibitors decreased both metabolism and binding in parallel, whereas scavenging agents for reactive oxygen species and free radicals exhibited little or no effect. Sulphur nucleophiles were extremely efficient in decreasing binding with little or no effect on metabolism. Reducing agents such as ascorbate and diaphorase decreased binding slightly more than metabolism. 3. UDP-Glucuronic acid inhibited neither metabolism nor binding, but all three mono-bromophenols decreased binding more than metabolism. Trichloropropene oxide was unique in decreasing metabolism more than binding. 4. The effects of ascorbate, glutathione, bisulphite and butylated hydroxytoluene (BHT) on metabolism and binding of five ortho-substituted bromobenzene derivatives (o-BrC6H4X; X = OCH3, CH3, Br, CF3, and CN) were similar to their effects on the metabolism and binding of bromobenzene. 5. Collectively these results support a major role for quinones as the reactive metabolites responsible for the majority of the protein covalent binding of bromobenzene and its ortho-substituted derivatives in microsomal systems in vitro.
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PMID:Effects of chemical and enzymic probes on microsomal covalent binding of bromobenzene and derivatives. Evidence for quinones as reactive metabolites. 340 Feb 72

The supernatant obtained by centrifugation of Triton N-101-treated freeze-dried rat testicular microsomal fraction at 105000g(av.) for 2h transformed progesterone into testosterone via 17-hydroxypregn-4-ene-3,20-dione and androst-4-ene-3,17-dione. Hydroxylation at C-17 of 3beta-hydroxypregn-5-en-20-one and deoxycorticosterone was not observed. Non-haem iron protein, cytochrome P-450 and material with NADPH dehydrogenase activity were precipitated by 40% saturation of the supernatant with ammonium sulphate; however, it was not possible to establish the participation of these substances in the 17alpha-hydroxylase and side-chain-cleavage activities also present in the precipitate. The results of gel-filtration chromatography indicated that the Triton N-101 extract consisted primarily of a suspension of small particles of microsomes and that the progesterone 17-hydroxylase and the 17-hydroxypregn-4-ene-3,20-dione side-chain-cleavage enzyme were not in true solution.
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PMID:Studies on an extract of rat testicular microsomal fraction that catalyses the transformation of progesterone into 17-hydroxyprogesterone and androgens. 512 59

The cytotoxicity of menadione (2-methyl-1,4-naphthoquinone) had been investigated using primary cultures of rat hepatocytes. Menadione was found to induce DNA strand breaks which were actively repaired by the cells. Dicoumarol, an inhibitor of DT diaphorase, did not potentiate menadione-induced DNA strand breaks. Neither had metyrapone, an inhibitor of cytochrome P-450 dependent monooxygenases, any effect on the extent of DNA damage. Covalent binding of menadione metabolite(s) to DNA was detected in the cultured hepatocytes and, in addition, hepatic microsomes were also found to metabolize menadione to DNA-binding products. The extent of binding of menadione to DNA in vitro, was markedly decreased by inclusion of the hepatic cytosol fraction, or reduced glutathione, in the incubations. In the presence of dicoumarol, menadione was also found to induce cell membrane damage. It also caused a rapid loss in cellular glutathione which was augmented by the presence of dicoumarol. The results suggest that both the cell membrane damage and DNA damage induced by menadione are mediated by one-electron reduction of the quinone to free radical intermediate(s). DT diaphorase appears to protect the cell from membrane damage, whereas reduced glutathione may have an important role in the prevention of DNA damage.
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PMID:Induction of DNA damage by menadione (2-methyl-1,4-naphthoquinone) in primary cultures of rat hepatocytes. 620 38

Cytochemistry was used to examine the distribution of two pathways of utilization of hydrogen (Type I and Type II H) generated by glucose-6-phosphate dehydrogenase (G6PD) in circumventricular organs (CVOs) and the hypothalamo-neurohypophysial system in cryostat sections of rat brain. Type I H is defined as that portion of the total reducing equivalents (Total H) that is passed, in the intact cells, along the cytochrome chain (NADPH-diaphorase system). In the liver, energy from Type I H is used for cytochrome P-450-dependent oxidation of steroids, as well as xenobiotics. We proposed that mixed function oxidation, and therefore Type I H, would be preferentially localized in brain regions lacking a blood-brain barrier, such as CVOs and magnocellular cells with terminals in such brain regions. Type I H was identified in tissue sections using neotetrazolium. This reagent, when reduced, precipitates as formazan granules that can be quantified. The large difference in redox potential between NADPH and neotetrazolium ensures that only hydrogen (Type I H) passed in the intact cell along the cytochrome chain, can reduce the tetrazole. Total NADPH generation (Total H) from glucose-6-phosphate, was identified using medium containing phenazine methosulphate, a hydrogen acceptor that transfers all reducing equivalents from NADPH to the tetrazole. Type II H, the difference between Total and Type I H, is presumed to be used for NADPH-dependent biosynthetic functions such as lipid synthesis, or reduction of glutathione. In CVOs formazan granules indicative of Type I H were selectively concentrated and localized within cells throughout the SFO, organum vasculosum of the lamina terminalis, pineal gland and in the apical cytoplasm of columnar ependymocytes in the subcommissural organ. Formazan granules attributable to Type I H were also prominent throughout the hypothalamo-neurohypophysial system. Reaction product was present in the cytoplasm of some magnocellular neurons in both the supraoptic and paraventricular nuclei, in the median eminence, including the zona interna, and in and between cells in the neurohypophysis. The distribution of NADPH-diaphorase in sections incubated with NADPH instead of glucose-6-phosphate was similar to that of Type I H. These findings are consistent with the hypothesis that mixed function oxidation involving NADPH and the cytochrome chain occur in these brain regions.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Pathways of hydrogen utilization from NADPH generated by glucose-6-phosphate dehydrogenase in circumventricular organs and the hypothalamo-neurohypophysial system: a cytochemical study. 669 40

Morphine elicited a dose-related increase in the duration of phencyclidine (PCP)-induced motor incoordination. In the open field behavioral observations, morphine enhanced the PCP-induced decrease in the number of ambulation and rearing. Morphine potentiated the PCP-induced decrease in body temperature. The LD50 of PCP was significantly decreased in the presence of morphine. An opiate antagonist, naloxone, antagonized the morphine-induced effects without influencing the pharmacological actions of PCP itself. The levels of hepatic microsomal cytochrome P-450 and cytochrome b5 and the activities of NADPH dehydrogenase and NADPH cytochrome c reductase were unaffected by morphine treatment. The half-lives of PCP in serum and brain were increased by the concurrent administration of morphine. The ratio of the liver weight to body weight and aniline hydroxylase activity in hepatic microsomal fraction were decreased in the morphine-treated group compared with the control group; this is indicative of a possible reduction in the oxidative metabolism of PCP. The results indicate that acute administration of morphine enhances a variety of pharmacological effects of PCP; an inhibition of PCP disposition by morphine may be a mechanism involved in this process.
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PMID:Effect of morphine on the responses to and disposition of phencyclidine in mice. I. Enhancement of phencyclidine effects by acute morphine administration. 684 96

This study was designed to assess the strain differences in pentobarbital toxicity, narcosis, the development of tolerance and physical dependence, the half-life of pentobarbital and the activities of hepatic microsomal electron transfer chain in DBA/2J, C57BL/6J and ICR mice. The comparisons of responses to acute pentobarbital-induced narcosis with two different doses revealed that DBA was most sensitive among these strains. When continuous administration of pentobarbital by pentobarbital pellet implantation is concerned, four criteria were used to assess strain differences: 1) determination of the duration of the loss of righting reflex during pentobarbital pellet implantation; 2) cumulative mortality after pentobarbital pellet implantation; 3) degree of tolerance development after 3 days of s.c. implantation of a 75-mg pentobarbital pellet by the relative decrease in the pentobarbital sleeping time; and 4) assessment of hyperexcitability by pentylenetetrazol- and audiogenic-induced seizures after pellet removal. The order of susceptibility to continuous pentobarbital pellet implantation was found to be as follows: DBA/2J > C57BL/6J > ICR. The biochemical data also revealed that the half-life of pentobarbital in DBA/2J mice was significantly longer than that of C57BL/6J or ICR mice in both brain and serum. Further studies also showed that DBA/2J mice have lower hepatic cytochrome P-450 and cytochrome b5 levels and NADPH dehydrogenase and NADPH-cytochrome c reductase activities as compared with the other strains of mice. However, these parameters were markedly induced in DBA/2J mice after the development of tolerance to pentobarbital. It appears that the differences in genetic variation could be of importance for further studies in gaining insight of the mechanism of barbiturate tolerance and dependence.
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PMID:Pharmacological responses to pentobarbital in different strains of mice. 719 35


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