The turnover of cytochrome P450b

Abstract
The turnover of the heme and apocytochrome moieties of phenobarbital‐inducible microsomal cytochrome P450 (P450b) was investigated. Adult male Sprague—Dawley rats were treated with phenobarbital for 5 days and injected with [35S]methionine and the heme precursor δ‐[3H]‐aminolevulinic acid. P450b was isolated by immunoprecipitation and quantitated by rocket immunoelectrophoresis. The isotope disappearance curves revealed a mean half‐life (T ) of 12.4 h for the heme moiety and a T of 19.1 h for the apoprotein moeity of P450b. The apparently slower catabolic rate of the apoprotein may be due to reutilization of [35S]methionine and does not exclude synchronous turnover of the two moieties. Our data are consistent with the kinetics of the drug‐mediated induction of cytochrome P450b.