1-Ethynylpyrene, a suicide inhibitor of cytochrome P-450 dependent benzo(a)pyrene hydroxylase activity in liver microsomes
The preparation of 1-ethynylpyrene (EP) by incubation of EP with liver microsomes in the presence of NADPH yields fluorescent products briefly. Addition of microsomes restores the original rate. The metabolism of EP is initially more rapid in microsomes from 5,6-benzoflavone- (BF) pretreated rats than in those from phenobarbital (PB) pretreated rats or controls. Ep inhibits the hydroxylation of benzo(a)pyrene (BP) by liver microsomes. Ep more effectively inhibits the oxidation of BP in liver microsomes from BF rats than from PB rats or from controls. The inhibition of BP hydroxylation activity due to EP is dependent upon NADPH and is apparently irreversible. Kinetic analyses show that the inhibition of BP hydroxylation is due to loss of the activity by a process that is first order in EP and that reaches a limiting value at infinite EP concentrations. A self-catalyzed inhibition of the cytochrome P-450 dependent BP hydroxylation may occur in the presence of EP. Incubation with EP under conditions that result in loss of BP hydroxylase activity in microsomes from BF rats and 66% of the activity from PB rats causes the loss of 6 and 12% of the cytochrome P-450, respectively. Thus the loss of P-450 content is an insensitive measure of the effect of this inhibitor upon this cytochrome P-450 dependent enzyme activity. Selectivity of the loss of P-450 due to the incubation of the different microsomal preparations with EP is observed to be different than the selectivity for loss of BP hydroxylase activity. It is proposed that the inhibition of cytochrome P-450 dependent enzymes by alkynes need not involve heme alkylation and a resulting loss of P-450 content. In vivo EP does not cause a significant change in the cytochrome P-450 content in the microsomes isolated, or result in the change in BP hydroxylation.
- Research Organization:
- Tulane Univ., New Orleans, LA
- OSTI ID:
- 5748563
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 23:17; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ALKYNES
ANIMALS
AROMATICS
BENZOPYRENE
BIOLOGICAL EFFECTS
BODY
CELL CONSTITUENTS
CONDENSED AROMATICS
CYTOCHROME OXIDASE
DIGESTIVE SYSTEM
ENZYME ACTIVITY
ENZYMES
GLANDS
HAEM DEHYDROGENASES
HYDROCARBONS
HYDROXYLATION
INHIBITION
LIVER
MAMMALS
MICROSOMES
ORGANIC COMPOUNDS
ORGANOIDS
ORGANS
OXIDOREDUCTASES
RATS
RODENTS
VERTEBRATES