Isolation and characterization of the basic forms of cytochrome P-450 from liver microsomes of C57BL mice after phenobarbital and 3-methylcholanthrene induction

Using hydrophobic and ion-exchange chromatography, cytochromes P-450 and P-448 from liver microsomes of C 57 BL mice induced by phenobarbital and 3-methylcholantrene were isolated. The cytochromes purified to homogeneity as evidenced from SDS polyacrylamide gel electrophoresis were characterized in terms of molecular weight and catalytic and spectral properties and by peptide mapping. Cytochrome P-450, in contrast to cytochrome P-448, was not bound to the ion-exchanger and was eluted in a void volume. Cytochrome P-450 (Mr = 51 000) elicits a low spin signal and reveals a high catalytic activity toward aminopyrine and a low catalytic activity toward benz(a)pyrene. Cytochrome P-448 (Mr = 55 000) elicits both high an low spin signals and reveals a high catalytic activity toward benz(a)pyrene and a low catalytic activity toward aminopyrine. Limited proteolysis with papain demonstrated the differences in the proteins primary structure.