Search results for "Microsome"
showing 10 items of 262 documents
Purification and characterization of rat-liver cytosolic epoxide hydrolase.
1988
Rat liver cytosolic epoxide hydrolase has been purified and characterized. The enzyme was purified from tiadenol-induced rat liver 540-fold with respect to trans-stilbene oxide as a substrate. Similar purification was obtained with the substrates trans-beta-ethyl styrene oxide and styrene 7,8-oxide, the specific activities decreasing in the order trans-beta-ethyl styrene oxide greater than styrene 7,8-oxide greater than trans-stilbene oxide. The enzyme exerts highest activity at pH 7.4 Km and Vmax of the pure enzyme for trans-stilbene oxide were 1.7 microM and 205 nmol x min-1 x mg protein-1 respectively. With trans-stilbene oxide as a substrate, the inhibition by organic solvents (2.5% by …
Modification of hepatic drug-metabolizing enzymes in rat fed naturally occurring allyl sulphides
1994
1. The effects of feeding allyl sulphides to rat (2000 ppm of the diet for 15 days) were investigated on various microsomal hepatic drug-metabolizing enzymes by their immunochemical detection and catalytic activity. 2. Allyl sulphides provoked a temporary dietary restriction, which enhanced the microsomal level of P450 and the activities of NADH-cytochrome c reductase and p-hydroxybiphenyl UDP-glucuronyltransferase (UDPGT 2), and lowered the activities of p-nitrophenol hydroxylase (PNPH), N-nitrosodimethylamine demethylase (NDMAD), laurate omega-hydroxylase (LAH) and glutathione S-transferase (GST). Therefore, pair-fed animals were used as a more relevant control for the dietary effects of …
Measurement of substrate-induced oxygen uptake during microsomal drug oxidation using a gold micro-electrode.
1975
1. A resin-coated gold micro-electrode has been used for polarographic determination of oxygen concentration in liver microsomal suspensions from phenobarbital-pretreated rats. 2. The rate of oxygen uptake on addition of an NADPH-regenerating system and the rate after addition of various substrates of the mixed function oxidase system were measured. The rate of oxygen uptake was faster in the presence of substrate than in the presence of NADPH alone. 3. Kinetic constants (Km and V max) for biphenyl, hexobarbital, ethylmorphine, naphthalene and SKF 525-A measured by this technique compare favourably with those obtained either by measurements of NADPH oxidation, or chemical measurements of su…
Metabolism of coumarin by precision-cut calf liver slices and calf liver microsomes.
1995
1. The metabolism of 50 microM [3-14C]coumarin has been studied in precision-cut-calf liver slices. 2. The metabolism of 50 microM coumarin to 7-hydroxycoumarin has also been examined in calf, rat, Cynomolgus monkey and human liver microsomal preparations. 3. In precision-cut calf liver slices, [3-14C]coumarin was metabolized to various polar products and to metabolite(s) that bound covalently to calf liver slice proteins. The polar products included 7-hydroxycoumarin (which was extensively conjugated with D-glucuronic acid and/or sulphate), metabolites of the 3-hydroxylation pathway (mainly o-hydroxyphenylethanol and o-hydroxyphenylacetic acid), and unknown metabolites. 4. Coumarin 7-hydro…
Inhibition of ethoxyresorufin deethylase activity by natural flavonoids in human and rat liver microsomes
1990
Several flavones and flavonols (chrysin, quercetin, luteolin, flavone and 7, 8-benzoflavone) were found to inhibit ethoxyresorufin deethylase (EROD) activity in human and rat liver microsomes. In man, molecules without hydroxyl groups are more powerful inhibitors than polyhydroxylated flavonoids (7, 8-benzoflavone greater than flavone greater than chrysin greater than luteolin greater than quercetin greater than morin). In rat, chrysin was the strongest inhibitor and the less effective were morin and 7,8-benzoflavone. For all molecules human microsomes were more sensitive than rat microsomes. The most important difference concerned 7,8-benzoflavone which was 10,000-fold more potent in man.
A novel haemoprotein induced by isosafrole pretreatment in the rat
1978
Abstract Sodium dodecyl sulphate-polyacrylamide gel electrophoresis has been used to demonstrate that pretreatment of rats with isosafrole results in the formation of a novel species of cytochrome P-450 (mol. wt. 54,000) quite distinct from that induced by phenobarbitone pretreatment (mol. wt. 50,000) or 3-methylcholanthrene (mol. wt. 58,000).
Irreversible protein binding of acrylonitrile.
1981
1. After i.p. injection of [2,3-14C]acrylonitrile to rats, a significant portion of radioactivity becomes irreversibly attached to proteins of liver, lung, spleen and other tissues. 2. When rat liver microsomes were incubated with [2,3-14C]acrylonitrile, a time-dependent irreversible binding of radioactivity occurred to microsomal proteins. This binding was not dependent on NADPH. A high extent of binding to heat-inactivated microsomes indicated that no enzymic metabolic step was involved. 3. The irreversible binding of [2,3-14C]acrylonitrile to rat liver microsomal protein in vitro was inhibited by thiols (cysteine, glutathione, mercaptoethanol). The greatest inhibitory potency was display…
On the spectral intermediate at 440 nm formed during mixed function substrate oxidation.
1974
Abstract The spectral shoulder formed at 440 nm in microsomes oxidising hexobarbital and other drugs has been investigated and some of its properties characterised. Hexobarbital, pentobarbital, ethylmorphine and barbital produce this shoulder, while acetanilide, aniline, desmethylimipramine, imipramine, metyrapone and SKF 525-A do not. The formation of the 440 nm shoulder depends on the presence of NADPH and oxygen and is reduced in size when NADH is also present. At saturating substrate concentrations the size of the 440 nm shoulder is correlated to the cytochrome P-450 content. The hexobarbital induced shoulder can be inhibited by drug metabolism inhibitors such as metyrapone, imipramine …
Isolation of a high spin form of cytochrome P-450 induced in rat liver by 3-methylcholanthrene.
1983
Abstract A form of cytochrome P-450 (P-450 MC1) has been isolated from the livers of 3-methylcholanthrene-treated rats. The molecular weight is 54,500 and the heme iron is in the high spin configuration which clearly differenciates this form from the other major cytochrome induced by 3-methylcholanthrene (P-450 MC2). Whilst MC2 actively dealkylated 7-ethoxycoumarin and 7-ethoxyresorufin, MC1 was only active with 7-ethoxyresorufin. Ouchterlony immunodiffusion analysis and ELISA showed that anti MC1 and anti MC2 reacted with both MC1 and MC2 but preferentially with the homologous antigen. Both anti MC1 and MC2 cross-reacted strongly with microsomes from 3-methylcholanthrene, Aroclor 1254 and …
Studies on the Biosynthesis of Microsomal Membrane Proteins. Site of Synthesis and Mode of Insertion of Cytochrome b5, Cytochrome b5 Reductase, Cytoc…
1982
The site of synthesis and mechanism of insertion into membranes of several microsomal polypeptides was studied using translation system programmed in vitro with polysomes or with mRNA extracted from free and membrane-bound rat liver polysomes. Primary translation products of cytochrome b5, NADH: cytochrome b5 oxidoreductase, NADPH: cytochrome P-450 oxidoreductase and epoxide hydrolase were isolated by specific immunoprecipitation and compared with the mature proteins. The following observations were made: 1 While cytochrome b5 and NADH: cytochrome b5 oxidoreductase are synthesized in free polysomes, NADPH: cytochrome P-450 oxidoreductase and epoxide hydrolase are made in membrane-bound poly…