Search results for "Microsomal epoxide hydrolase"
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The membrane anchor of microsomal epoxide hydrolase from human, rat, and rabbit displays an unexpected membrane topology.
1997
The microsomal epoxide hydrolase (mEH) and cytochrome P450s catalyze the sequential formation of carcinogenic metabolites. According to one algorithm for predicting the membrane topology of proteins, the human, the rabbit, and the rat mEH should adopt a type II topology. The type II topology is also predicted by a recently established neuronal network which is trained to recognize signal peptides with very high accuracy. In contrast to these predictions we find, based on N-glycosylation analysis in a cell-free and in a cellular system, that the membrane anchor of human, rat, and rabbit mEH displays a type I topology. This result is correctly predicted by the positive inside rule in which ne…
Comparison of enzyme phenotypes in human bladder tumours and experimentally induced hyperplastic and neoplastic lesions of the rat urinary bladder. A…
1988
The expression of a number of enzymes involved in drug metabolism, membrane function etc. was compared in hyperplastic and neoplastic lesions of the rat bladder and in human bladder tumours. Transitional cell carcinomas (TCC) in both rat and Man were characterized by decreased alkaline phosphatase (ALP) and increased gamma-glutamyl transpeptidase (GGT), beta-glucuronidase (beta-G1), succinate dehydrogenase (SD) and glucose-6-phosphate dehydrogenase (G6PD) activities. In addition, binding for antibodies specific for different cytochrome P-450 species (UT50, PB3a, MC1, MC2) and microsomal epoxide hydrolase (mEHb) was elevated in both murine and human tumours. Comparison of the enzyme phenotyp…
Studies on the importance of microsomal epoxide hydrolase in the detoxification of arene oxides using the heterologous expression of the enzyme in ma…
1994
In order to investigate the role of the microsomal epoxide hydrolase (mEH) in the detoxification of arene oxides in the presence of a high endogenous glutathione S-transferase (GST) activity-a situation found in several organs--we expressed the rat mEH cDNA in BHK21 Syrian hamster cells. These cells have high GST activities but contain an extremely low endogenous mEH enzyme activity. We obtained several cell clones which expressed the mEH heterologously, as determined by immunoblotting. The cell clone BHK21-mEH/Mz1 had the highest level of mEH protein. Immunofluorescence showed that the level of expression was almost homogeneous throughout the cell population. Total protein isolated from th…
Microsomal Biotransformation of Benzo[ghi]perylene, a Mutagenic Polycyclic Aromatic Hydrocarbon without a “Classic” Bay Region
2005
Carcinogenic polycyclic aromatic hydrocarbons (PAH), e.g., benzo[a]pyrene (BaP), possess a bay region comprising an ortho-fused benzene ring. Benzo[ghi]perylene (BghiP) represents the group of PAHs lacking such a "classic" bay region and hence cannot be metabolically converted like BaP to bay region dihydrodiol epoxides considered as ultimate mutagenic and carcinogenic metabolites of PAH. BghiP exhibits bacterial mutagenicity in strains TA98 (1.3 his(+)-revertant colonies/nmol) and TA100 (4.3 his(+)-revertant colonies/nmol) of Salmonella typhimurium after metabolic activation by the postmitochondrial hepatic fraction of CD rats treated with 3-methylcholanthrene. Inhibition of microsomal epo…
Time-dependence and differential induction of rat and guinea pig peroxisomal beta-oxidation, palmitoyl-CoA hydrolase, cytosolic and microsomal epoxid…
1988
Fischer-344 rats and Hartley guinea pigs received a diet containing 0.01% (w/w), 0.05% (w/w), or 0.25% (w/w) of the hypolipidemic drug fenofibrate. Rats were treated for 4, 7, 14, or 21 days, and a clear dose-dependent and weak time-dependent increase in liver/body weight ratio was observed. The specific activity of peroxisomal beta-oxidation increased linearly with time at all concentrations used. A dose-dependent increase in cEH was observed, but the activity remained constant after treatment for 7 days. Enhancement of palmitoyl-CoA hydrolase was dose-dependent, but was similar at all 4 time points investigated. In contrast to the other enzyme activities, mEH was not or only minimally (le…
Structure of Aspergillus niger epoxide hydrolase at 1.8 A resolution: implications for the structure and function of the mammalian microsomal class o…
2000
AbstractBackground: Epoxide hydrolases have important roles in the defense of cells against potentially harmful epoxides. Conversion of epoxides into less toxic and more easily excreted diols is a universally successful strategy. A number of microorganisms employ the same chemistry to process epoxides for use as carbon sources.Results: The X-ray structure of the epoxide hydrolase from Aspergillus niger was determined at 3.5 Å resolution using the multiwavelength anomalous dispersion (MAD) method, and then refined at 1.8 Å resolution. There is a dimer consisting of two 44 kDa subunits in the asymmetric unit. Each subunit consists of an α/β hydrolase fold, and a primarily helical lid over the…
Dependency of the in vitro stabilization of differentiated functions in liver parenchymal cells on the type of cell line used for co-culture.
1992
The differentiation status in cultures of primary rat liver parenchymal cells was determined by measuring the activities of various xenobiotic metabolizing enzymes. Most enzyme activities dropped rather rapidly in monocultures of parenchymal cells. The protein content and the activities of cytosolic epoxide hydrolase, glutathione S-transferase, and alpha-naphthol UDP-glucuronosyl transferase were, however, well stabilized in 7-day-old co-cultures of parenchymal cells with two different lines of rat liver nonparenchymal epithelial cells (NEC1 and NEC2). Phenol sulfotransferase and microsomal epoxide hydrolase activity were reduced in this coculture system after 7 days to about 30 and 20% of …
Recombinant expression of human microsomal epoxide hydrolase protects V79 Chinese hamster cells from styrene oxide- but not from ethylene oxide-induc…
1997
Styrene 7,8-oxide and ethylene oxide are widely used genotoxic bulk chemicals, which have been associated with potential carcinogenic hazard for occupationally exposed workers. Both epoxides alkylate DNA preferentially at the N-7 position of guanine and consequently produce single-strand breaks and alkali labile sites in the DNA of exposed cells. In order to study the role of human microsomal epoxide hydrolase (hmEH) in protecting cells against genotoxicity of styrene 7,8-oxide and ethylene oxide, we expressed the cDNA of hmEH in V79 Chinese hamster cells. We obtained a number of cell clones that expressed functionally active epoxide hydrolase. Among these, the clone 92hmEH-V79 revealed an …
Rat and human liver cytosolic epoxide hydrolases: evidence for multiple forms at level of protein and mRNA.
1990
Two forms of human liver cytosolic epoxide hydrolase (cEH) with diagnostic substrate specificity for trans-stilbene oxide (cEHTSO) and cis-stilbene oxide (cEHCSO) have been identified, and cEHCSO was purified to apparent homogeneity. The enzyme had a monomer molecular weight of 49 kDa and an isoelectric point of 9.2. Pure cEHCSO hydrolyzed CSO at a rate of 145 nmole/min/mg. TSO was not metabolized at a detectable level, and like cEHTSO, the enzyme was about three times more active at pH 7.4 than at pH 9.0. Unlike cEHTSO, cEHCSO was efficiently inhibited by 1 mM 1-trichloropropene oxide (90.5%) and 1 mM STO (92%). Similarly, liver cEH purified 541-fold from fenofibrate induced Fischer 344 ra…
The gap junctional intercellular communication is no prerequisite for the stabilization of xenobiotic metabolizing enzyme activities in primary rat l…
1995
In primary monocultures of adult rat liver parenchymal cells (PC), the activities of the xenobiotic metabolizing enzymes microsomal epoxide hydrolase (mEHb), soluble epoxide hydrolase (sEH), glutathione S-transferases (GST), and phenolsulfotransferase (ST) were reduced after 7 d to values below 33% of the initial activities. Furthermore, the gap junctional intercellular communication (GJIC), measured after microinjection by dye transfer, decreased from 90% on Day 1 to undetectable values after 5 d in monoculture. Co-culture of PC with nonparenchymal rat liver epithelial cells (NEC) increased (98% on Day 1) and stabilized (82% on Day 7) the homotypic GJIC of PC. Additionally, most of the mea…