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Title: Metabolism of benzene and phenol by a reconstituted purified phenobarbital induced rat liver mixed function oxidase system

Abstract

Cytochrome P-450 and the electron-donor, NADPH-cytochrome c reductase were isolated from phenobarbital induced rat liver microsomes. Both benzene and its primary metabolite phenol, were substrates for the reconstituted purified phenobarbital induced rat liver mixed function oxidase system. Benzene was metabolized to phenol and the polyhydroxylated metabolites; catechol, hydroquinone and 1,2,4 benzenetriol. Benzene elicited a Type I spectral change upon its interaction with the cytochrome P-450 while phenol's interaction with the cytochrome P-450 produced a reverse Type I spectra. The formation of phenol showed a pH optimum of 7.0 compared with 6.6-6.8 for the production of the polyhyrdoxylated metabolites. Cytochrome P-450 inhibitors, such as metyrapone and SKF 525A, diminished the production of phenol from benzene but not the production of the polyhydroxylated metabolites from phenol. The radical trapping agents, DMSO, KTBA and mannitol, decreased the recovery of polyhydroxylated metabolites, from /sup 14/C-labeled benzene and/or phenol. As KTBA and DMSO interacted with OH. There was a concomitant release of ethylene and methane, which was measured. Desferrioxamine, an iron-chelator and catalase also depressed the recovery of polyhydroxylated metabolites. In summary, benzene and phenol were both substrates for this reconstituted purified enzyme system, but they differed in binding to cytochrome P-450, pH optima andmore » mode of hydroxylation.« less

Authors:
Publication Date:
Research Org.:
Rutgers--the State Univ., New Brunswick, NJ (USA)
OSTI Identifier:
6619142
Resource Type:
Thesis/Dissertation
Resource Relation:
Other Information: Thesis (Ph. D.)
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; BENZENE; METABOLISM; MIXED-FUNCTION OXIDASES; CHEMICAL ACTIVATION; PHENOL; CARBON 14 COMPOUNDS; CYTOCHROMES; LIVER; MICROSOMES; PHENOBARBITAL; ANESTHETICS; ANTICONVULSANTS; AROMATICS; AZINES; BARBITURATES; BODY; CELL CONSTITUENTS; CENTRAL NERVOUS SYSTEM DEPRESSANTS; DIGESTIVE SYSTEM; DRUGS; ENZYMES; GLANDS; HETEROCYCLIC COMPOUNDS; HYDROCARBONS; HYDROXY COMPOUNDS; HYPNOTICS AND SEDATIVES; LABELLED COMPOUNDS; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; ORGANOIDS; ORGANS; OXIDOREDUCTASES; OXYGENASES; PHENOLS; PIGMENTS; PROTEINS; PYRIMIDINES 550201* -- Biochemistry-- Tracer Techniques

Citation Formats

Griffiths, J.C.. Metabolism of benzene and phenol by a reconstituted purified phenobarbital induced rat liver mixed function oxidase system. United States: N. p., 1986. Web.
Griffiths, J.C.. Metabolism of benzene and phenol by a reconstituted purified phenobarbital induced rat liver mixed function oxidase system. United States.
Griffiths, J.C.. 1986. "Metabolism of benzene and phenol by a reconstituted purified phenobarbital induced rat liver mixed function oxidase system". United States. doi:.
@article{osti_6619142,
title = {Metabolism of benzene and phenol by a reconstituted purified phenobarbital induced rat liver mixed function oxidase system},
author = {Griffiths, J.C.},
abstractNote = {Cytochrome P-450 and the electron-donor, NADPH-cytochrome c reductase were isolated from phenobarbital induced rat liver microsomes. Both benzene and its primary metabolite phenol, were substrates for the reconstituted purified phenobarbital induced rat liver mixed function oxidase system. Benzene was metabolized to phenol and the polyhydroxylated metabolites; catechol, hydroquinone and 1,2,4 benzenetriol. Benzene elicited a Type I spectral change upon its interaction with the cytochrome P-450 while phenol's interaction with the cytochrome P-450 produced a reverse Type I spectra. The formation of phenol showed a pH optimum of 7.0 compared with 6.6-6.8 for the production of the polyhyrdoxylated metabolites. Cytochrome P-450 inhibitors, such as metyrapone and SKF 525A, diminished the production of phenol from benzene but not the production of the polyhydroxylated metabolites from phenol. The radical trapping agents, DMSO, KTBA and mannitol, decreased the recovery of polyhydroxylated metabolites, from /sup 14/C-labeled benzene and/or phenol. As KTBA and DMSO interacted with OH. There was a concomitant release of ethylene and methane, which was measured. Desferrioxamine, an iron-chelator and catalase also depressed the recovery of polyhydroxylated metabolites. In summary, benzene and phenol were both substrates for this reconstituted purified enzyme system, but they differed in binding to cytochrome P-450, pH optima and mode of hydroxylation.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1986,
month = 1
}

Thesis/Dissertation:
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  • The catalytic properties of purified cytochrome P-450b, the major isozyme found in hepatic microsomes from phenobarbital-pretreated rats, for the metabolism of N-methylcarbazole (NMC) were analyzed in two membranous systems in order to investigate membrane bilayer-dependent parameters. Incorporation of the enzymes of the monoxygenase system into bilayer liposomal vesicles composed of total microsomal lipid had no effect on the rates or regioselectivity of the mono-hydroxylation of the substrate when compared to the same enzymes reconstituted in a soluble system with small amounts of dilauroylphosphatidylcholine (DLPC). The membranous system exhibited K/sub m/ values of NMC which were 4-5 times higher than themore » non-vesicular system. The rapid decline in the rates of NMC metabolism by cytochrome P-450b during catalysis suggested enzyme inactivation during substrate processing. Radiolabel from (methyl-/sup 14/C)NMC was incorporated into the P-450b apoprotein as a result of enzyme turnover co-incident with the loss of enzyme activity. NMC-stimulated NADPH oxidation by the reconstituted enzyme system containing DLPC was biophasic, with a slow rate preceding a two-fold higher rate. Carbazole and some N-substituted derivatives were unique in stimulating this unusual oxidation.« less
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