Related Experiment Videos
Purification and partial characterization of hepatic microsomal cytochrome P-450s from phenobarbital- and
Abstract:
Hepatic microsomal cytochrome P-450 and P-448 have been purified from phenobarbital (PB)- and 3-methylcholanthrene (MC)-treated rats, by modifications of Imai and Sato's procedures )1974). The purified preparations of cytochrome P-450 and P-448 were homogeneous judging from their specific contents (17 and 16 nmol per mg protein, respectively) and the results of SDS-polyacrylamide gel electrophoresis and Ouchterlony immunodiffusion analyses. These two cytochromes are different in their physico-chemical and immunological properties, and their substrate specificities. In reconstituted systems containing the purified cytochrome and NADPH-cytochrome P-450 reductase, ethoxycoumarin deethylation and benzo(a)pyrene hydroxylation catalyzed by cytochrome P-450 and P-448 were completely inhibited by the homologous antibody, while essentially no effect was observed with heterologous conbinations of antigen and antibody. In contrast, the benzphetamine demethylation activities of cytochrome P-450 and P-448 were markedly inhibited by the heterologous antibody as well as by the homologous one. These results suggest that the two cytochromes are immunologically different but have some antigenic determinants in common. Drug metabolizing activities of microsomes from PB- and MC-treated rats were inhibited by the antibodies, essentially as expected from the results with the reconstituted systems. The remaining activities in the presence of excess concentrations of the antibody, however, were higher in MC-microsomes treated with anti P-448 antibody than in PB microsomes treated with anti P-450 antibody. These results suggest that cytochrome P-448 molecules may be so localized in the microsomal membrane that the membrane structure may hinder the access of the antibody to the antigenic determinant.
Insights
Hepatic cytochrome P-450 and P-448, purified from rats, show distinct immunological properties and substrate specificities. Antibodies confirm their differences but also shared antigenic sites, impacting drug metabolism studies.
Area of Science:
- Biochemistry
- Pharmacology
- Molecular Biology
Background:
- Cytochrome P-450 (CYP) enzymes are crucial for drug metabolism.
- Phenobarbital (PB) and 3-methylcholanthrene (MC) induce distinct CYP isoforms.
- Understanding CYP heterogeneity is key to predicting drug interactions.
Purpose of the Study:
- To purify and characterize hepatic microsomal cytochrome P-450 and P-448.
- To investigate the immunological and functional differences between these two cytochromes.
- To assess their roles in drug metabolism using specific antibodies.
Main Methods:
- Purification of cytochrome P-450 and P-448 from PB- and MC-treated rat liver microsomes.
- Homogeneity assessment using SDS-PAGE and Ouchterlony immunodiffusion.
- Reconstitution assays with purified cytochromes and NADPH-cytochrome P-450 reductase.
- Enzyme activity assays (ethoxycoumarin deethylation, benzo(a)pyrene hydroxylation, benzphetamine demethylation) with homologous and heterologous antibodies.
Main Results:
- Purified cytochrome P-450 and P-448 were homogeneous and immunologically distinct.
- Homologous antibodies completely inhibited specific substrate metabolism in reconstituted systems.
- Heterologous antibodies showed cross-reactivity in benzphetamine demethylation, indicating shared antigenic determinants.
- Inhibition patterns in microsomes mirrored reconstituted systems, with differences suggesting membrane localization effects for P-448.
Conclusions:
- Cytochrome P-450 and P-448 are distinct isoforms with unique properties.
- Immunological cross-reactivity exists, but specific antibodies are valuable tools.
- Microsomal localization may influence antibody accessibility and interpretation of drug metabolism studies.