Metabolic-intermediate complex formation reveals major changes in rat hepatic cytochrome P-450 subpopulations in addition to those forms previously purified after phenobarbital, beta-naphthoflavone, and isosafrole induction.

By coupling a simple separatory procedure with the ability of cytochrome P-450 subpopulations to sequester themselves a metabolic-intermediate (MI) complexes, previously undocumented alterations of cytochrome P-450 subpopulations by inducing agents have been detected. Phenobarbital induces at least two forms of cytochrome P-450 differing in their chromatographic properties and molecular weight, with neither form possessing the ability to generate MI complexes from isosafrole. beta-Naphthoflavone induces at least two forms having different chromatographic properties, molecular weights and abilities to generate MI complexes; these two forms differ from both of the forms induced by phenobarbital. Isosafrole induces at least three forms, all of which generate MI complexes but which differ from each other in chromatographic properties and molecular weight. Thus, in addition to the well-characterized forms of cytochrome P-450, phenobarbital, beta-naphthoflavone, and isosafrole also cause changes in heretofore uncharacterized forms, and it is these "other" forms which are responsible for the changes in isosafrole MI complex formation seen after beta-naphthoflavone and phenobarbital treatment.