Characterization of three forms of cytochrome P-450 inducible by 3-methylcholanthrene in Golden hamster livers with special reference to aflatoxin B1 activation

Three forms of cytochrome P-450 of liver microsomes of 3-methylcholanthrene-treated Golden hamsters were purified and characterized as regards their catalytic activity toward aflatoxin B1-related hepatocarcinogenic mycotoxins. These include two major forms, designated as cytochrome P-450-AFB (P-450-I) and P-450-II, and one minor form, P-450-III. Cytochromes P-450-AFB, P-450-II, and P-450-III have their absorption maximum in the carbon monoxide-complex of the reduced form at 448.5, 447.0, and 448.0 nm, have apparent molecular weights of 56,000, 58,000, and 59,500, and are in the low spin, high spin, and low spin state, respectively. Of these, cytochrome P-450-AFB was shown to be highly active in the mutagenic activation of aflatoxin B1-related hepatocarcinogens such as sterigmatocystin and O-methylsterigmatocystin. Activation of aflatoxin B1 by hepatic microsomes of 3-methylcholanthrene-treated hamsters was inhibited almost completely by the antibody against P-450-AFB but not by the antibody against P-450-II, indicating that P-450-AFB is the major component responsible for the activation of aflatoxin B1 by hamster liver. Western blot analysis demonstrated that no protein cross-reacted with the antibody to P-450-AFB in the liver microsomes from guinea pig, rat, mouse, and house musk shrew (Suncus murinus) treated with 3-methylcholanthrene, while one or two proteins cross-reacted with the antibody to P-450-II in the liver microsomes of these animals.