Abstract

Characteristics of mixed-function oxidases in the liver of house musk shrew, Suncus murinus, were studied. The basal level of cytochrome P-450 and the activity of drug-metabolizing enzyme in hepatic microsomes of Suncus murinus is relatively lower than that of rats, while the level of cytochrome b5 and NADPH-cytochrome c reductase is approximately the same as that of rats. The treatment of Suncus murinus with phenobarbital and 3-methylcholanthrene elevated the level of cytochrome P-450 and the activity of drug-metabolizing enzymes, but not the level of cytochrome b5. Two distinct forms of cytochrome P-450 have been purified from hepatic microsomes of 3-methylcholanthrene-treated Suncus murinus. These forms have their absorption maximum at 448.0 nm and 448.5 nm in CO-bound reduced form, and one is in the high-spin state and the other is in the low-spin state. They are different in their molecular weights (53,500 and 55,000) and in their spectral and catalytic properties. Characteristics of these forms were compared with those of the major forms of cytochrome P-450 purified from livers of rats treated with 3-methylcholanthrene.