TY - JOUR T1 - Induction of Drug Metabolism JF - Molecular Pharmacology JO - Mol Pharmacol SP - 372 LP - 382 VL - 9 IS - 3 AU - D. W. SHOEMAN AU - FLOIE M. VANE AU - G. J. MANNERING Y1 - 1973/05/01 UR - http://molpharm.aspetjournals.org/content/9/3/372.abstract N2 - Cytochromes P-450 and P1-450 (P-448), found predominantly in hepatic microsomes from untreated and from 3-methylcholanthrene-treated rats, respectively, are reported to be distinct molecular entities. To test this hypothesis, a comparison was made of soluble P-420 hemoproteins obtained from membrane-bound P-450 hemoproteins by digesting microsomes with steapsin. Partially purified, soluble cytochromes P-420 and P1-420 from microsomes from untreated and 3-methylcholanthrene-treated rats, respectively, were found to differ in their electrophoretic mobilities and in the molar absorbances of their carbon monoxide complexes (P-420, 110 mM-1 cm-1; P1-420, 134 mM-1 cm-1); when caused to aggregate, cytochrome P-420 exhibited both type I (hexobarbital) and type II (aniline difference spectra, but aggregated cytochrome P1-420 exhibited a type II difference spectrum only. That cytochrome P1-450 is not simply a complex of cytochrome P-450 with 3-methylcholanthrene or its metabolites was demonstrated by the failure of soluble, purified cytochrome P1-420 from rats treated with tritiated 3-methylcholanthrene to exhibit radioactivity. These studies support the view that cytochromes P-450 and P1-450 are distinct molecular entities. ER -