Search results for "Microsoma"
showing 8 items of 78 documents
Endogenous Role of Microsomal Epoxide Hydrolase
2005
The specific activities of microsomal epoxide hydrolase with 16α,17α-epoxyandrosten-3-one (androstene oxide) as substrate were measured in various metabolically important and in various steroidogenic organs of the male and female rat and compared with the activities of 16α,17α-epoxyestratrienol (estroxide) and benzo[a]pyrene 4,5-oxide. Androstene oxide was an exceptionally good substrate. The specific activities differed widely between organs but the ratio of the activities towards these substrates was constant in all organs investigated. The ratios compared to benzo[a]pyrene 4,5-oxide were 2.5 for estroxide, and 8.6 for androstene oxide. The ontogenetic development of specific epoxide hydr…
Stable Expression of Heterologous Microsomal Epoxide Hydrolase in BHK21 Cells: Influence on the Mutagenicity of Benzo[a]pyrene 4,5-Oxide
1992
Most environmental mutagens and carcinogens require metabolic activation to electro- philic intermediates capable of reacting with cellular target structures, such as DNA. These electrophilic intermediates are in addition subject to metabolic detoxification. This metabolism is mainly controlled by enzymes whose expression is very variable. Among other things, various enzymes are inducible by environmental chemicals. Understanding the toxicology of chemicals (for example, species differences, idiosyncrasias, organotropisms) therefore requires knowledge of critical host factors. One approach towards this goal involves the use of purified enzymes in metabolism and toxicological studies (Glatt …
Role of the Well-Known Basic and Recently Discovered Acidic Glutathione S-Transferases in the Control of Genotoxic Metabolites
1991
Glutathione S-transferases (GSTs; E.C. 2. 5. 1. 18) are a family of enzymes which have increasingly attracted the interest of toxicologists, pharmacologists, biochemists and clinicians since their discovery in 1961 (1). Initially, GSTs were believed to serve as intracellular transport proteins for endogenous compounds with limited solubility in water, thus acting as an intracellular equivalent to albumin in blood plasma. In this assumed capacity of reversible binding and transport of various ligands, the corresponding protein was named ligandin (2). Following the discovery of abundant GST occurrence in most forms of aerobic life including plants, and the GST-catalysed conjugation of a wide …
Species Differences in Enzymes Controlling Reactive Epoxides
1987
Activities of enzymes involved in the metabolic formation and catabolism of epoxides were determined in liver subcellular preparations from 11 mammalian species and various strains of mice. The most conspicuous finding was that the activities of the microsomal epoxide hydrolase were clearly lower in the mouse than in the other species. This invited the working hypothesis that epoxides may be involved in mouse liver carcinogenesis. The carcinogens may be metabolised themselves to reactive epoxides or they may modify the metabolism of epoxides formed from endogenous or other foreign compounds. To examine the former point, phenobarbital, DDT (1,1-bis(p- chlorophenyl)-2,2,2-trichloroethane), li…
Epoxide Hydrolase Isoenzymes and their Individual Contribution to the Control of Toxic Metabolites
1991
Epoxides are highly strained three membered cyclic ethers which are formed in vivo by the microsomal cytochrome P450 dependent monooxygenases as intermediates of several important biosynthetic pathways (leukotriene A4, squalene 2, 3-oxide) and as metabolites of numerous xenobiotic compounds containing olefinic or aromatic double bonds. Further transformation of these epoxides may occur by either, rearrangement to phenols, aliphatic aldehydes, or ketones; by cytochrome P450 dependent reduction to the parent compound; or by spontaneous or enzymatic conjugation to gluta-thione. Epoxides may also bind covalently to cellular nucleophiles, such as proteins and nucleic acids thus eliciting carcino…
Relationship between rat liver microsomal Δ6 and Δ5 desaturase activities and fatty acid composition: comparative effects of coconut and salmon oils …
1992
International audience; The aim of this work was to compare the effects of coconut and salmon oils on rat liver microsomal Δ6 and Δ5 desaturations, during protein restriction. A higher Δ6 desaturase activity was noted in rats fed the low-protein coconut oil diet, in comparison with that occurring in rats fed either a low-protein or normal-protein salmon oil diet. No variation was observed in Δ5 desaturase activity or in 20:4n-6/ 18:2n-6 ratio. The fatty acid composition of liver microsomal phospholipids provided evidence of higher levels of 20:5n-3 and 22:6n-3 in the normal-protein salmon oil group, when compared with the low-protein salmon oil group. No influence of experimental diets on t…
Genetics of familial hypobetalipoproteinemia
2007
Primary hypobetalipoproteinemias include three monogenic disorders: the relatively frequent codominant familial hypobetalipoproteinemia (FHBL), the rare recessive conditions abetalipoproteinemia (ABL) and chylomicron retention disease (CMRD). Approximately 50% of FHBL patients are carriers of mutations in the APOB gene, mostly causing the formation of truncated forms of ApoB. In some kindred, FHBL is linked to a locus on chromosome 3 (3p21), but the candidate gene is still unknown. Recently, a FHBL-like phenotype was observed in carriers of mutations of the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene causing loss-of-function of the encoded protein, a proprotein convertase tha…
Focal elevation of liver microsomal epoxide hydrolase in early preneoplastic stages and its behaviour in the further course of hepatocarcinogenesis.
1981
Abstract Treatment of rats with N-nitrosomorpholine (NNM) for 7 weeks led to a focal increase in liver microsomal epoxide hydrolase (EH) as early as 2 weeks after withdrawal of the carcinogen. This treatment also leads to hyperplastic nodules and liver tumors, but much later. At the same early time point, ATPase activity was decreased in the same islands. Most of these areas already had increased γ-glutamyltranspeptidase activity. The increase in EH at this early time point was more distinct than the decrease in ATPase which has thus far been considered a suitable marker of the earliest stages in hepatocarcinogenesis. The focal increase in EH was also observed in all benign hepatomas, but n…