Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “HYDRASES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
PubMed1989

Metabolism and hepatorenal toxicity due to repeated exposure to styrene in spontaneously hypertensive rats (SHR).

Groups of adult male rats (5 rats per group), either normotensive (WKY) or spontaneously hypertensive (SHR), were exposed by inhalation to 0, 821, and 3018 ppm styrene, 5 h per day for 3 consecutive days. After the exposure, the urines were collected for 24 h and the animals were then sacrificed. The various biochemical parameters of hepatorenal toxicity due to styrene as well as its urinary metabolites were measured. Hepatotoxicity due to styrene was not further increased at any exposure level due to hypertension. However, repeated exposure of SHR rats to 3018 ppm styrene showed significant increases in the urinary excretion of gamma-glutamyl transpeptidase, proteins, and volume of urine, compared to WKY treated rats, whereas no such changes were observed due to repeated exposure to 821 ppm styrene. Studies of in vivo metabolism of styrene at higher exposure level showed significant decrease in the urinary excretion of mandelic, phenylglyoxylic, and hippuric acids in SHR rats compared to WKY-treated rats, suggesting an inhibition of deactivation of styrene reactive intermediate involving the epoxide hydrase pathway due to hypertension. At the same time, a significant increase in the urinary excretion of a potential nephrotoxic metabolite of styrene (e.g., mercapturates or thioethers) was observed in SHR-treated rats when compared to WKY-treated rats. These results demonstrate that spontaneous hypertension has the potential to further increase the nephrotoxicity due to repeated exposure to styrene, and the metabolism of styrene plays an important role in modifying such toxicity in the hypertensive state.

Acetylglucosaminidase↗
PubMed1980

Correlation between transformation potential and inducible enzyme levels of hamster embryo cells.

When benzo(a)pyrene was used to evaluate the transformability of 129 hamster embryo cell preparations from pooled or individual embryos, approximately 50% of the cultures were transformable. A transformable and a non-transformable cell culture were further tested with other carcinogens (3-methylcholanthrene [MCA], benzyl chloride, ethyl-p-toluenesulfonate, 2-naphthylamine, and aflatoxin B1). The transformable culture responded to all of the carcinogens while the non-transformable culture always gave negative results. Aryl hydrocarbon hydroxylase (AHH) and epoxide hydrase (EH) levels were compared in the two cell cultures using beta-naphthoflavone (BNF), benz(a)anthracene (BA), sodium phenobarbital (PB) or MCA as microsomal enzyme-inducing agents. It was found that AHH levels and the degree of induction following treatment of the cells with BNF or BA were consistently higher in the transformable than in the non-transformable cells following treatment with either BNF, BA, PB or MCA. Inducible AHH and EH levels might, therefore, be useful as predictors of the transformation potential of hamster embryo cell cultures.

Animals↗
PubMed1989

Binding of 7H-dibenzo[c,g]carbazole to polynucleotides and DNA in vitro.

The N-heterocyclic aromatic pollutant, 7H-dibenzo[c,g]carbazole (DBC), is a potent carcinogen having both local and systemic effects. The overall objective of this research was to investigate the nature of the covalent binding of DBC with nucleic acids in vitro. DBC was shown to bind to polynucleotides, RNA and DNA in an in vitro rat or hamster microsomal enzyme assay, exhibiting a preferential binding to polyguanylic acid (poly[G]). Benzo[a]pyrene (BaP) binding to these same nucleic acids was determined simultaneously and was approximately 10-fold higher than DBC binding under identical experimental conditions. DBC-nucleic acid binding was shown to be dependent upon the presence of a microsomal activating system, the results being similar for rat or hamster liver microsomes. This microsome-dependent binding was unaffected by the addition of epoxide hydrase activity modifiers but was almost completely inhibited by alpha-naphthoflavone. The nature of DBC-nucleic acid binding was investigated using fluorescence spectroscopy. Benzo[c]carbazole and 5,5,6,6-tetrahydrodibenzo[c,g]carbazole were synthesized as representatives of the effect of disruption of the DBC pi-electron system on fluorescence excitation and emission. DBC-poly[G] adducts were isolated from binding assay mixtures and separated by HPLC. Results indicated that there are at least three different DBC-poly[G] adducts formed in vitro. The emission spectra of isolated adducts were similar in shape to that of DBC; however, the adduct spectra were shifted 5-10 nm toward longer wavelengths. This suggests that the bound DBC species have intact pi-electron systems. Results are consistent with binding through the nitrogen position as well as binding through the 1,2,3,4-ring of the molecule.

Animals↗
PubMed1995

The hepatic metabolism of two carcinogenic dimethylbenz[c]acridines in control and induced rats: the distribution and the mutagenicity of metabolites.

The major and minor metabolites of the potent polycyclic aza-aromatic carcinogens 7,9-dimethylbenz[c]acridine and 7,10-dimethylbenz[c]acridine, and the stereochemistry of the dihydrodiol metabolites have been previously described. The metabolite distributions produced in incubations of the aza-aromatic compounds with liver microsomes from phenobarbital- and 3-methylcholanthrene-pretreated and untreated rats, and the mutagenicity in the Ames test are described in this paper. The major metabolites of each were the alcohols produced by oxidation of the methyl group on the 8,9,10,11-ring for control and phenobarbital-induced preparations, while with 3-methylcholanthrene-induced preparations both the 7- and 9- (or 10-) monoalcohols were formed. Total monofunctionalized dihydrodiol metabolites, the 5,6- and 3,4-isomers for 7,9-dimethylbenz[c]acridine, and the 3,4-, 5,6- and 8,9-isomers for 7,10-dimethylbenz[c]acridine, constituted approximately 10% of total metabolites. As well, the K-region arene oxide was formed in substantial amounts with both compounds, accompanied in the case of 7,10-dimethylbenz[c]acridine with some 8,9-oxide. When incubations were carried out in the presence of the epoxide hydrase inhibitor 3,3,3-trichloropropane-1,2-oxide, dihydrodiol formation was almost completely inhibited and relative amounts of both phenols and oxides increased. Secondary metabolites were also formed to approximately 10% of the total products. The mutagenicity of synthetic alcohols and isolated purified metabolites was determined in the Salmonella mammalian microsome plate assay (Ames test) with strain TA100. Limited amounts of metabolites isolated precluded extensive testing, but high mutagenicities were noted for all 3,4-dihydrodiol derivatives isolated. These exceeded those of the parent aza-aromatic hydrocarbons. Alcohols were also active but less so than the parent compounds. The activation of these two dimethylbenz[c]acridines to mutagens appears to be through bay-region diolepoxides following patterns seen in other aza-aromatic compounds and the polycyclic aromatic hydrocarbons.

Acridines↗
PubMed1985

Modification of aflatoxin B1 binding to DNA in vivo in rats fed phenolic antioxidants, ethoxyquin and a dithiothione.

The effects of dietary administration of 3,5-di-tert-butyl-4-hydroxytoluene (BHT), 2(3)-tert-butyl-4-hydroxyanisole (BHA), ethoxyquin (EQ) and 5-(2-pyrizinyl)-4-methyl-1,2-dithiol-3-thione (oltipraz) on aflatoxin B1 (AFB1) - DNA adduct formation in vivo in livers and kidneys of rats were investigated. Male F344 rats were treated with 1 mg/kg AFB1 by i.p. administration and nucleic acids isolated 2 h post dosing. Animals were fed a semipurified diet supplemented with either 0.5% EQ, 0.45% BHT, 0.45% BHA or 0.1% oltipraz for 2 weeks prior to AFB1 treatment. Analysis of nucleic acid bases by h.p.l.c. showed that several AFB1 metabolite-DNA adducts were formed in both tissues. The principal and related adducts of 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 represented approximately 80-90% of all adducts in both tissues and in all treatment groups. However, inclusion of the antioxidants in the diet resulted in substantial reductions in overall AFB1 modified DNA levels. EQ, BHT, BHA and oltipraz reduced the covalent binding of AFB1 to liver DNA by 91, 85, 65 and 76% and to kidney DNA by 80, 35, 62 and 64%, respectively. Concordantly, the specific activities of hepatic enzymes of presumed importance to AFB1 detoxification, epoxide hydrase, and glucuronyl and glutathione transferases were significantly elevated by all antioxidants. Reduced glutathione levels were unchanged except by oltipraz, although activities of enzymes contributing to the maintenance of reduced glutathione pools, glutathione reductase and glucose-6-phosphate dehydrogenase, were elevated in most treatment groups. An excellent correlation (r = 0.95) was observed between the degree of inhibition of DNA binding by AFB1 and the induction of hepatic glutathione S-transferase activities by the four antioxidants.

Aflatoxin B1↗
PubMed1986

Oxidative microsomal metabolism of 1-nitropyrene and DNA-binding of oxidized metabolites following nitroreduction.

1-Nitropyrene is an environmental mutagen and carcinogen which undergoes both oxidative and reductive metabolism. We have previously shown that nitroreduction to N-hydroxy-1-aminopyrene leads to the formation of arylamine--DNA adducts. In the present study, we have investigated the oxidative metabolism of 1-nitropyrene and the subsequent binding of ring-oxidized metabolites to DNA. In vitro incubations were conducted using hepatic microsomes from uninduced rats or from rats pretreated with phenobarbital, Aroclor 1254, 3-methylcholanthrene, or 3-methylcholanthrene and trans-stilbene oxide. H.p.l.c. analysis of the incubation mixtures indicated the presence of the previously reported metabolites, 1-aminopyrene, 3-, 6-, and 8-hydroxy-1-nitropyrene, and 1-nitropyrene trans-4,5-dihydrodiol. In addition, 1-nitropyrene 4,5-oxide, 1-nitropyrene 9,10-oxide, 1-nitropyrene trans-9,10-dihydrodiol and 1-pyrenol were identified. The formation of both K-region dihydrodiols could be increased by trans-stilbene oxide induction of microsomal epoxide hydrase. Formation of the K-region epoxides was greatest using phenobarbital- and Aroclor-induced microsomes and increased with increasing oxygen tension, while 1-pyrenol formation was highest in 3-methylcholanthrene-induced microsomal incubations and was not affected by the oxygen tension. When calf thymus DNA was added to the microsomal incubations, similar levels of DNA-binding occurred in incubations conducted under oxygen, air, argon or anaerobic conditions. H.p.l.c. analysis of the enzymatically hydrolyzed DNA indicated the presence of multiple DNA adducts with the major product coeluting with N-(deoxyguanosin-8-yl)-1-aminopyrene. The K-region oxides bound directly to DNA to give adducts similar to the minor products detected in the microsomal incubations. Incubation of the K-region oxides with the nitroreductase, xanthine oxidase, increased the DNA-binding and resulted in an additional adduct which coeluted with N-(deoxyguanosin-8-yl)-1-amino pyrene. 3-Hydroxy-1-nitropyrene bound extensively to DNA upon nitroreduction by rat liver cytosol or xanthine oxidase, while 6- and 8-hydroxy-1-nitropyrene bound only slightly. None of these oxidized metabolites was activated to DNA-binding species by cytosolic nitroreduction followed by AcCoA-dependent acetylation. The fact that oxidized metabolites of 1-nitropyrene are reduced to DNA-binding derivatives more easily than 1-nitropyrene itself may be important in vivo where 1-nitropyrene has been shown to be readily oxidized.

Acetylation↗
PubMed1987

In vivo and in vitro formation of glutathione conjugates from the K-region epoxides of 1-nitropyrene.

4,5-Epoxy-4,5-dihydro-1-nitropyrene (1-nitropyrene 4,5-oxide) and 9,10-epoxy-9,10-dihydro-1-nitropyrene (1-nitropyrene 9,10-oxide), which are electrophilic metabolites formed during the metabolism of the environmental pollutant, 1-nitropyrene, reacted slowly with glutathione. The rate of conjugation was greatly enhanced by the addition of purified rat liver glutathione (GSH) transferases, with transferases 3-3 and 4-4 exhibiting higher catalytic activities than transferases 1-1, 2-2 and 7-7. Two GSH conjugates were formed from each of the oxides: 1-nitropyrene 4,5-oxide gave a 1:1 mixture of 4-(glutathion-S-yl)-5-hydroxy-4,5-dihydro-1-nitropyrene and 5-(glutathion-S-yl)-4-hydroxy-4,5-dihydro-1-nitropyrene while 1-nitropyrene 9,10-oxide gave a 2:1 mixture of 9-(glutathion-S-yl)-10-hydroxy-9,10-dihydro-1-nitropyrene and 10-(glutathion-S-yl)-9-hydroxy-9,10-dihydro-1-nitropyrene. Both K-region oxides were converted to trans-dihydrodiols by hepatic microsomal epoxide hydrase, and faster rates were observed with 1-nitropyrene 4,5-oxide. In subsequent experiments [4,5,9,10-3H]1-nitropyrene was administered to Sprague-Dawley rats by intravenous and intraperitoneal injections. HPLC analysis of biliary metabolites indicated the presence of four GSH conjugates that were identical to those obtained from reactions of the K-region oxides with GSH. In addition, glucuronide conjugates were detected from trans-4,5-dihydroxy-4,5-dihydro-1-nitropyrene (1-nitropyrene trans-4,5-dihydrodiol) but not trans-9,10-dihydroxy-9,10-dihydro-1-nitropyrene (1-nitropyrene trans-9,10-dihydrodiol). These data combined with earlier studies indicate that 1-nitropyrene is oxidized preferentially to 1-nitropyrene 4,5-oxide and that, while the main detoxification pathway of 1-nitropyrene 9,10-oxide is GSH conjugation, 1-nitropyrene 4,5-oxide is excreted via both GSH conjugation and dihydrodiol formation followed by O-glucuronidation.

Animals↗
PubMed1987

Stability of drug metabolizing enzymes during the incubation conditions of the liver microsomal assay with non-induced and induced mouse liver S-9 fractions.

The purpose of this work was to study the relative activities and stabilities of phase-I and phase-II drug metabolizing enzymes in incubation mixtures used in vitro genotoxicity testing in order to optimize the conditions of the assay, increase sensitivity and eliminate false negative results. Cytochrome P-450, NADPH-cytochrome P-450 (cytochrome c) reductase activity and various phase-I and phase-II enzyme activities of the drug-metabolizing system were determined in incubation mixtures used in liver microsomal assays. The behaviour of aminopyrine N-demethylase and p-nitroanisole O-demethylase activities as phase-I markers have been reported previously. Other activities measured were glutathione S-transferase, glutathione S-epoxide transferase and epoxide hydrase, and lipid peroxidation (LP) was determined. The experiments were carried out on liver S9 fractions derived from non-induced mice or mice induced with sodium phenobarbital (PB), and/or beta-naphthoflavone (beta-NF). The phase-II enzymes were much more stable (70-90% residual activity) than phase-I enzyme activities (35-60%) in all conditions tested. The residual cytochrome P-450 was approximately 70% stable and the remaining activity of NADPH-cytochrome c-reductase about 80%, indicating that this latter enzyme does not limit the rate of the monoxygenase system in these conditions. Phase-II enzymes were induced to a smaller extent (about 2 times) than in phase-I enzymes (5-6 times) by beta-NF + PB. NADPH-cytochrome c-reductase behaved as phase-II enzymes in this respect as well as for stability. LP was appreciably higher in non-induced than in induced animals. Treatment with the beta-NF + PB mixture, however, showed that induced enzymes were more stable than those obtained by simple induction with either beta-NF or PB alone. These results lead to the conclusion that prolonged incubation times in mutagenicity assays are unnecessary when considering the relative stabilities of the various phase-I and phase-II enzyme activities in the drug-metabolizing system.

Animals↗
PubMed1988

DNA binding by 1-nitropyrene and 1,6-dinitropyrene in vitro and in vivo: effects of nitroreductase induction.

1-Nitropyrene, the predominant nitropolycyclic aromatic hydrocarbon found in diesel exhaust, is a mutagen and tumorigen. 1,6-Dinitropyrene is present in diesel exhaust in much smaller quantities than 1-nitropyrene, but is much more mutagenic and carcinogenic. In an attempt to understand this difference in biological potencies, we have compared the extent of DNA binding by these two nitropyrenes in vivo. We have also determined the effect of 1-nitropyrene pretreatment upon the induction of nitroreductases and the subsequent DNA binding by both 1-nitropyrene and 1,6-dinitropyrene. Covalent DNA binding by 1-nitropyrene could not be detected in vivo; however, 1,6-dinitropyrene formed N-(deoxyguanosin-8-yl)-1-amino-6-nitropyrene as the major DNA adduct in rat liver, kidney, urinary bladder and mammary gland, with the highest levels being found in the bladder. The capability of liver microsomes to catalyze the oxidative metabolism of 1-nitropyrene was unchanged after treating rats with 8 mg/kg 1-nitropyrene. Cytochrome P-450, NADPH-cytochrome P-450 reductase and cytochrome b5 levels were also unchanged, while slight increases were detected in NADH-cytochrome b5 reductase and epoxide hydrase activities. Liver cytosolic and microsomal nitroreductase activities toward both 1-nitropyrene and 1,6-dinitropyrene were increased 2-fold, and cytosolic nitrosoreductase activity toward 1-nitrosopyrene and 1-nitro-6-nitrosopyrene was elevated by approximately 20%. DNA binding of both 1-nitropyrene and 1,6-dinitropyrene in vitro was 2-fold higher when using cytosol from 1-nitropyrene-pretreated rats. However, pretreatment of rats with 1-nitropyrene only slightly increased the amount of in vivo DNA binding by 1,6-dinitropyrene except in kidney where there was a 60% increase. These results indicate that although nitroreduction is involved in DNA adduct formation by 1,6-dinitropyrene, additional factors (e.g. O-acetylation) limit the extent of DNA binding in vivo.

Animals↗
PubMed1977

Effect of trichloropropene oxide on the ability of polyaromatic hydrocarbons and their "K-region" oxides to initiate skin tumors in mice and to bind to DNA in vitro.

The potent epoxide hydrase inhibitor, 1,1,1-trichloro-2,3-propene oxide (TCPO), enhanced the tumor-initiating ability of benzo[alpha]pyrene (BP) and 3-methylcholanthrene (MCA) but had no effect on 9,10-dimethyl-1,2-anthracene (DMBA) initiation in a two-stage system of tumorigenesis in female Charles River CD-1 mice. The tumor-initiating ability of dibenz[alpha,h]-anthracene (DBA) was decreased by prior topical treatment with 10 mumoles of TCPO. The tumor latency period of BP and MCA was decreased by TCPO but had no effect on DMBA or DBA. Topical treatment with 10 mumoles of TCPO did not initiate tumors in a two-stage system in mouse skin nor did it cause any histopathologic changes in the skin. The "K-region" epoxides of BP, DMBA, and MCA were weak tumor initiators when compared to the parent compounds. TCPO only slightly increased or had no effect on the tumor-initiating activity of the above epoxides. Pretreatment with Croton oil 18 hours prior to initiation with BP-4,5-epoxide also slightly enhanced the tumorigenic response in mouse skin. DBA-5,6-epoxide, when tested as a complete carcinogen at high doses (1 mg daily/10 days), was found to be a weak carcinogen but with activity comparable to that of DBA. TCPO only slightly increased the in vitro epidermally mediated covalent binding of the above parent polycyclic hydrocarbons to DNA.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1986

Synthesis and mutagenicity of 1-nitropyrene 4,5-oxide and 1-nitropyrene 9,10-oxide, microsomal metabolites of 1-nitropyrene.

[4,5,9,10-(3)H]1-Nitropyrene was incubated with liver microsomes prepared from guinea pigs treated with Aroclor 1254 and the products were examined by h.p.l.c. The previously reported metabolites, 1-nitropyrene trans-4,5-dihydrodiol, 1-nitropyrene trans-9,10-dihydrodiol, and 3-, 6-, and 8-hydroxy-1-nitropyrene were detected. In addition, h.p.l.c., nuclear magnetic resonance and mass spectral analyses indicated the presence of 1-nitropyrene 4,5-oxide and 1-nitropyrene 9,10-oxide. The epoxide hydrase inhibitor, 1,2-epoxy-3,3,3-trichloropropane, decreased the concentration of the 4,5- and 9,10-dihydrodiols in the microsomal incubations and increased the concentration of their corresponding oxides. Reaction of 1-nitropyrene with m-chloroperoxybenzoic acid gave a mixture of 1-nitropyrene 4,5-oxide and 1-nitropyrene 9,10-oxide, which was separated by chromatography. The mutagenicity of the oxides was determined in Salmonella typhimurium strains TA98, TA98NR, and TA98/1,8-DNP6, both with and without exogenous activation by a rat liver homogenate fraction (S9). In the absence of S9, both oxides showed maximum activity in TA98, slightly decreased mutagenicity in the acetylase-deficient strain TA98/1,8-DNP6, and much reduced activity in the nitroreductase-deficient strain, TA98NR. When assayed in the presence of S9, 1-nitropyrene 4,5-oxide had maximum mutagenicity in TA98, and was 50 and 95% less mutagenic in TA98NR and TA98/1,8-DNP6, respectively. 1-Nitropyrene 9,10-oxide had a similar strain sensitivity, except that its total mutagenicity was lower. Since 1-nitropyrene is metabolized by oxidative pathways in vivo, these K-region oxides may contribute to the toxicities elicited by this compound.

Animals↗
PubMed1983

Carbamazepine and its major metabolites in plasma: a summary of eight years of therapeutic drug monitoring.

For a period of 8 years, carbamazepine (CBZ) and its two major metabolites carbamazepine-10,11-epoxide (CBZE) and 10,11-dihydroxy-carbamazepine (CBZH) were monitored in plasma of black and white patients visiting outpatient epilepsy clinics. Mean CBZ, CBZE, and CBZH levels found in the black group (n = 451) were found to be significantly lower (p less than 0.0005) than in white patients (n = 2,225). The ratio of CBZE to CBZ levels was found to be significantly lower (p less than 0.0005) for blacks, with CBZ levels within the therapeutic range (5-10 micrograms/ml); the ratio of CBZH to CBZ levels was higher (p less than 0.0005), while there was no significant difference in the ratio of CBZH to CBZE between the two groups. This may indicate a difference in the monooxygenase enzyme activities, whereas the epoxide hydrase activity is probably the same for both groups. A poor linear correlation exists between CBZH and CBZ levels in both groups (for blacks, r = 0.614, n = 451; for whites, r = 0.338, n = 2,225); the correlation is better between CBZE and CBZ (for blacks, r = 0.745; for whites, r = 0.553) and good between CBZH and CBZE (for blacks, r = 0.752; for whites, r = 0.710). Abnormal ratios of CBZH to CBZE were found to be useful indicators of noncompliance in difficult cases presenting with therapeutic levels of CBZ.

Black People↗
PubMed1990

Expression of carbonic anhydrase in neisseriae and other heterotrophic bacteria.

A diverse range of heterotrophic bacteria was screened for the presence of carbonic anhydrase (CA) activity, sensitivity to inhibition of growth by acetazolamide (CA inhibitor), and the presence of protein binding monospecific antibody prepared against purified Neisseria sicca CA. CA activity was demonstrated only in strains of N. sicca and N. gonorrhoeae. However, all Neisseria strains, including various isolates of N. meningitidis and N. lactamica, were sensitive to acetazolamide, when grown in air, and showed serological cross-reaction with N. sicca CA. Strains of other genera were resistant to acetazolamide. A number of strains including members of the genera Pseudomonas, Staphylococcus, Streptococcus, Serratia and Proteus also strongly expressed a gene product(s) immunologically related to CA. The presence of CA cross-reacting proteins, which lack hydrase activity, is discussed in relation to the function of the various mammalian CA isoenzymes.

Acetazolamide↗
PubMed2003

Crystallization and preliminary X-ray diffraction analysis of thermophilic imidase from pig liver.

Imidase is an enzyme, also known as dihydropyrimidinase (EC 3.5.2.2), hydantoinase, dihydropyrimidine hydrase or dihydropyrimidine amidohydrolase, that catalyzes the reversible hydrolysis of 5,6-dihydrouracil to 3-ureidopropionate and many other imides. Substrate specificity, metal content and amino-acid sequence all differ significantly between bacterial and mammalian imide-hydrolyzing enzymes. In this study, a thermophilic imidase was isolated from pig liver and crystallized. Two kinds of imidase crystals were grown by the hanging-drop vapour-diffusion method using polyethylene glycol MME 5000 and 2-propanol as precipitants. One belongs to the triclinic P(1) space group, with unit-cell parameters a = 96.35, b = 96.87, c = 154.87 A, alpha = 82.10, beta = 72.54, gamma = 77.19 degrees, and the other belongs to the orthorhombic C222(1) space group, with unit-cell parameters a = 113.92, b = 157.22, c = 156.21 A.

Amidohydrolases↗
PubMed1976

Distribution of cholesterol-5alpha,6alpha-epoxide formation and its metabolism in mouse skin.

The distribution of cholesterol-5alpha,6alpha-epoxide in ultraviolet light-irradiated mouse skin was determined. Highest levels of cholesterol-5alpha,6alpha-epoxide were found in the epidermis and distributed rather evenly throughout all subcellular fractions. Low but potentially significant levels of the compound diffused from the epidermis. Metabolic studies demonstrated that cholesterol-5alpha,6alpha-epoxide was converted to cholestane-3ss,5alpha,6ss-triol by an enzyme, cholesterol-5alpha,6alpha-epoxide hydrase, which was localized in the epidermal fractions sedimenting at 10,000 and 100,000 X g. Comparative studies indicated a much higher capacity for metabolism of cholesterol-5alpha,6alpha-expoide in liver than in skin. The effect of the epoxide and its metabolic product on the skin is discussed.

Animals↗
PubMed1978

The mechanism of action of cytochrome P-450. Occurrence of the 'NIH shift' during hydroperoxide-dependent aromatic hydroxylations.

The mechanism of liver microsomal aromatic hydroxylation has been investigated by using cumene hydroperoxide as the hydroxylating agent and comparing this reaction with the NADPH-dependent reaction. The conversion of [4-(3)H]acetanilide to 4-hydroxyacetanilide by rat liver microsomes (or purified cytochrome P-450) in the presence of either cumene hydroperoxide or NADPH is attended by comparable 'NIH shifts'. This indicates that hydroxylation in the two systems proceeds via a common intermediate, presumably an arene oxide. The intermediacy of an arene oxide, phenanthrene-9,10-oxide, is established by incubating [3-(3)H]-phenanthrene with rat-liver microsomes and cumene hydroperoxide in the presence of either non-radioactive phenanthrene-9,10-oxide as a 'trap' or in the presence of cyclohexene oxide, an inhibitor of the enzyme epoxide hydrase. Incubation of phenanthrene with cumene hydroperoxide in an 18O-enriched medium has confirmed that the oxygen atom in phenanthrene-9,10-oxide is derived from the hydroperoxide and not from the medium.

Acetanilides↗
PubMedDate not supplied

Halothane hepatitis: damage to peripheral blood mononuclear cells produced by electrophilic drug metabolites is Ca(2+)-dependent.

Peripheral blood mononuclear (PBM) cells from patients with halothane hepatitis are unusually susceptible to damage from phenytoin metabolites generated by an in vitro drug metabolising system. In order to provide more information about the nature of this susceptibility factor, the effect of removing calcium ions (Ca2+) from the incubation medium of the test system was examined. Phenytoin metabolites were generated by incubating phenytoin with beta-naphthoflavone-induced rat liver microsomes in the presence of 1,1,1-trichloropropene oxide (TCPO), an epoxide hydrase inhibitor. When PBM cells from patients who had recovered from halothane hepatitis were incubated in this system and then maintained in Ca(2+)-containing tissue culture medium (without alpha-tocopherol) for 16 h, cell death, as measured by trypan blue exclusion, was greatly increased (53% and 78% at 0.06 mmol/l and 0.12 mmol/l phenytoin, respectively) compared with control incubations (TCPO omitted). Removal of Ca2+ from the tissue culture medium effectively abolished reactive metabolite-induced cell death. Resting cytosolic free Ca2+ concentration in PBM cells was also measured using the quin-2 fluorescence method and total Ca2+ content was measured by atomic absorption spectrometry. Although variability appeared greater among patients, mean values for these parameters among 12 patients with halothane hepatitis did not differ from controls. It is concluded that enhanced permeability of PBM cells to extracellular Ca2+ may be an important factor in the pathogenesis of drug metabolite-induced cell death in patients susceptible to halothane hepatitis. Such permeability to Ca2+ is not evident in resting cells and presumably results from an interaction between electrophilic metabolites and the pumps which regulate cell calcium homeostasis.

Calcium↗
PubMed1981

Tricaine (MS-222) induced modification on the metabolism of foreign compounds in the liver and duodenal mucosa of the splake (Salvelinus fontinalis X Salvelinus namaycush).

The splake, a popular game fish, is a crossbreed which must be reared in nurseries. The fish are marked under anesthesia for later study. We analyze the effect of a common anesthetic, tricaine (MS-222), on the metabolism of foreign compounds in the liver and duodenum of the splake. In the liver and to some extent in the duodenum, aryl hydrocarbon hydroxylase and epoxide hydrase activities were reduced during treatments. The ethoxycoumarin O-deethylase activities were not affected in either the liver or duodenum. Tricaine significantly decreased the hepatic UDP-glucuronosyltransferase activity. The decrease was greater when the aglycone used was p-nitrophenol than with methylumbelliferone. A similar effect was also found after trypsin treatment of the microsomes. No significant decrease in the UDP-glucuronosyltransferase activity was detected in the duodenal mucosa. This was the case when both p-nitrophenol and methylumbelliferone were used as aglycones.

Aminobenzoates↗