Multiple Forms of Cytochrome P-450 in Phenobarbital- and 3-Methylcholanthrene-treated Rats

Multiple forms of liver microsomal cytochrome P-450 isolated from immature male rats pretreated with phenobarbital or 3-methylcholanthrene are described. A fraction. of low specific content (Fraction A, 1.7 to 4.0 nmol of cytochrome P-450 per mg of protein) and a fraction substantially purified (Fraction B, 9.0 to 11.0 mnol of cytochrome P-450 per mg of protein) are obtained by DEAE-cellulose chromatography of a partially purified cytochrome P-450 preparation in the presence of Emulgen 911. Shifts in the absorption maxima in the CO-reduced and ethyl isocyanide difference spectra are observed in the fractions derived from 3-methylcholanthrene-treated rats. The fractions derived from phenobarbital-treated rats exhibit different 455:430 ratios and pH intercepts in the ethyl isocyanide difference spectra. The absolute oxidized spectra and n-octylamine binding spectra at room temperature and EPR analysis at the temperature of liquid helium characterize all the fractions, except the Fraction A from 3-methylcholanthrene-treated rats, as low spin ferric hemeproteins. The A hemeprotein fractions from both 3-methylcholanthreneand phenobarbital-treated rats have poor catalytic activity for the metabolism of benzphetamine and 3,4-benzo[alpyrene in comparison to the B hemeprotein fractions which may be due to the presence of a high concentration of Emulgen 911 in the A fractions. However, the presence of Emulgen 911 cannot account for the spectral differences among the fractions.