Induction of a phenobarbital-inducible form of cytochrome P-450 in rat liver microsomes by 1,1-di(p-chlorophenyl)-2,2-dichloroethylene.

Abstract

When 1,1-di(p-chlorophenyl)-2,2-dichloroethylene (DDE) (100 mg/kg body weight) was injected into rats, the benzphetamine N-demethylation and 7-ethoxycoumarin O-deethylation activities of liver microsomes increased by 7-fold and 3-fold, respectively, at 7 days after the injection, whereas the benzo(a)pyrene 3-hydroxylation activity did not increase. The content of cytochrome P-450 in the microsomes increased 2.5-fold at 7 days. By the use of the antibodies to a phenobarbital (PB)-inducible form (P-450(PB-1)) and a 3-methylcholanthrene (MC)-inducible form (P-450(MC-1)) of cytochrome P-450, the contents of P-450(PB-1) and P-450(MC-1) in the liver microsomes of DDE-treated rats were measured. The form of cytochrome P-450 immunoprecipitable with anti-P-450(PB-1) antibodies increased by 10-fold at 7 days. A major component of cytochrome P-450 in the liver microsomes of DDE-treated rats, which was tentatively designated P-450(DDE), was purified. P-450 (DDE) was compared with P-450(PB-1), and they were found to be indistinguishable by the following criteria: 1) chromatographic behavior on aminooctyl-Sepharose 4B, hydroxyapatite, and DEAE-cellulose columns, 2) minimum molecular weight determined by SDS-polyacrylamide gel electrophoresis, 3) spectral properties, 4) immunoreactivity, 5) amino acid composition, 6) peptide mapping, 7) NH2-terminal amino acid sequence, 8) catalytic activities. We concluded that DDE and PB induce an identical form of P-450 in rat liver microsomes, although DDE is apparently very different from PB in chemical structure.