Influence of Sex Hormones on Relative Quantities of Multiple Species of Cytochrome P‐450 in Rat Liver Microsomes: A Possible Answer to the Sexual Differences in Metabolic Activities of Rat Liver Microsomes

EPR spectra of rat liver microsomes from male, female and hormonally‐treated castrated hepatectomized rats were studied. The spectra, especially in the region of g_max, suggested a heterogeneity of local environments of the low spin ferric heme indicative of multiple structures for cytochrome P‐450. Certain features in the spectrum correlated with sexual differences. It is suggested that the changes in the relative amplitudes of the EPR features represent differences in the relative abundance of the individual proteins in the mixture that, in turn, are related to the sexual differences of metabolic patterns for reactions catalyzed by cytochrome P‐450.