Search results for "microsomes"
showing 10 items of 193 documents
Phosphorylation of rabbit liver cytochrome P-450 LM2 and its effect on monooxygenase activity
1984
The phosphorylation of rabbit liver microsomal cytochrome P-450 LM2 by catalytic subunit of cyclic AMP-dependent protein kinase (W. Pyerin et al. (1983) Carcinogenesis 4, 573) has now been studied in detail with purified soluble form of cytochrome P-450 as well as with the purified protein incorporated into model membranes. The apparent Km values for P-450 of the phosphorylation reaction in all experimental systems were in a range of 2-8 microM, while the Vmax values were dependent on the state of P-450. Upon phosphorylation, the reconstituted enzyme activities with benzphetamine (N-demethylation) and 7-ethoxycoumarin (O-deethylation) as substrates were reduced to 30-40% of control.
NADPH-cytochrome P-450 reductase: Preferential inhibition by ellipticine and other type II compounds having little effect on NADPH-cytochrome c reduc…
1980
Abstract Ellipticine (5,11-dimethyl-[6H]-pyrido[4,3b]carbazole) binds with an affinity greater than most other compounds known to interact with P-450. Control and 3-methylcholanthrene-induced aryl hydrocarbon (benzo[ a ]pyrene) hydroxylase (EC 1.14.14.2) and acetanilide 4-hydroxylase and control and phenobarbital-induced ethylmorphine N -demethylase activities are all markedly inhibited by ellipticine to about the same extent. Ellipticine and other Type II compounds (metyrapone, octylamine-1, pyridine and aniline) preferentially inhibit NADPH-cytochrome P-450 reductase activity, while affecting NADPH-cytochrome c reductase activity very little. Butanol-1, a compound having pure Reverse Type…
Kinetic experiments on the binding of metyrapone to liver microsomes
1969
Kinetic experiments on the inhibition of oxidative microsomal O- and N-demethylations by metyrapone (2-methyl-1, 2-bis(3-pyridyl)-l-propanone, Su 4885) were carried out using mouse liver microsomes as the enzyme source. The model substrates were p-nitroanisole and N-monomethyl-p-nitroaniline. It was shown that the inhibition is competitive. The K i for metyrapone is 0.42 × 10−4 M and for the reduced metabolite of metyrapone 1.15×10−4 M. Their spectral dissooiation constants as determined from difference spectra have almost the same values. From this it is concluded that the degree of inhibition is correlated to the amount of metyrapone bound to cytochrome P-450. Metyrapone does not seem to …
Cytoplasmic autoantigens in autoimmune hepatitis: molecular analysis and clinical relevance.
1991
Biomarker responses of the earthworm Aporrectodea tuberculata to copper and zinc exposure: differences between populations with and without earlier m…
2003
Biomarkers in the earthworm Aporrectodea tuberculata (Eisen) were measured to find out their possible induction under Cu and Zn exposure and differences in the responses between two populations with different exposure history. The biomarkers applied were concentration of metallothioneins (MT), and cytochrome P4501A (CYP1A) monooxygenase and glutathione-S-transferase (GST) activities. These were measured from earthworms sampled at three distances from a steel smelter in Finland and from the individuals from two populations, one with and another without earlier metal exposure, exposed to three combined Cu/Zn concentrations in the laboratory. In the field, MT concentration, and cytochrome CYP1…
Contribution of CYP3A5 to the in vitro hepatic clearance of tacrolimus.
2005
Abstract Background: Tacrolimus is metabolized predominantly to 13-O-demethyltacrolimus in the liver and intestine by cytochrome P450 3A (CYP3A). Patients with high concentrations of CYP3A5, a CYP3A isoenzyme polymorphically produced in these organs, require higher doses of tacrolimus, but the exact mechanism of this association is unknown. Methods: cDNA-expressed CYP3A enzymes and a bank of human liver microsomes with known CYP3A4 and CYP3A5 content were used to investigate the contribution of CYP3A5 to the metabolism of tacrolimus to 13-O-demethyltacrolimus as quantified by liquid chromatography–tandem mass spectrometry. Results: Demethylation of tacrolimus to 13-O-demethyltacrolimus was …
An insect juvenile hormone-specific epoxide hydrolase is related to vertebrate microsomal epoxide hydrolases.
1996
Abstract We describe the first cDNA sequence encoding a juvenile hormone-specific epoxide hydrolase from an insect. A full-length cDNA clone revealed a 462-amino-acid open reading frame encoding an amino acid sequence with 44% identity and 64% similarity to human microsomal epoxide hydrolase. All residues in the catalytic triad (residues Asp 227 -His 428 -Asp 350 in the M. sexta protein) were present, as was the conserved Trp 154 corresponding to the oxyanion hole. The surprising similarity of insect juvenile hormone epoxide hydrolase to vertebrate microsomal epoxide hydrolases, coupled with the ancient lineage of the epoxide hydrolases and haloalkane dehalogenases, suggests that this catab…
Hepatic metabolism of diclofenac: role of human CYP in the minor oxidative pathways.
1999
The aim of this study was to re-examine the human hepatic metabolism of diclofenac, with special focus on the generation of minor hydroxylated metabolites implicated in the idiosyncratic hepatotoxicity of the drug. Different experimental approaches were used: human hepatocytes, human microsomes, and engineered cells expressing single human CYP (cytochromes P450). Human hepatocytes formed 3'-hydroxy-, 4'-hydroxy-, 5-hydroxy- 4',5-dihydroxy-, and N,5-dihydroxydiclofenac, as well as several lactams. Formation of 4'- and 5-hydroxydiclofenac by human liver microsomes followed a Michaelis-Menten kinetics (Km 9 +/- 1 microM; Vmax 432 +/- 15 pmol/min/mg and Km 43 +/- 5 microM; and Vmax 15.4 +/- 0.6…
Epoxides derived from various polycyclic hydrocarbons as substrates of homogeneous and microsome-bound epoxide hydratase. A general assay and kinetic…
1976
A general assay for epoxide hydratase using epoxides derived from polycyclic aromatic hydrocarbons as substrates is described. Addition of dimethylsulphoxide to the incubation mixture after incubation allowed unreacted epoxide and its phenolic by-product to be extracted into light petroleum whilst the product dihydrodiol remained in the aqueous phase. The product was then extracted into ethyl acetate and estimated radiochemically. This assay gave low extraction blanks (0.8-3.8%) when six K-region epoxides of polycyclic hydrocarbons were used, with high recoveries of the corresponding dihydrodiol in the ethyl acetate phase (65-89%). Radiochromatograms demonstrated that all the radioactivity …