Cytochrome P-450 dependent deethylase activity in rat and hairless mouse skin microsomes

Microsomal fractions were prepared from rat and hairless mouse skin. The method of preparation was validated by studying the distribution of succinate dehydrogenase, acid phosphatase and UDP-glucuronosyltransferase. Induction of oxidative deethylation activities by 5,6-benzoflavone and 3-methylcholanthrene was investigated. Preparations from hairless mouse skin exhibited higher basal activities but the enzymes were less responsive than those of rat skin to inducers. Species differences were observed in the extent of induction between topical and i.p. administration of 5,6-benzoflavone, the former route being more effective in the hairless mouse and the latter route most effective in the rat. Generally oxidative deethylation activity increased linearly with protein concn up to 2-3 mg protein/ml. The only exception was rat skin microsomes prepared from animals pretreated with 5,6-benzoflavone, where linearity was observed only to 0.75 mg protein/ml above which oxidative deethylation activity decreased with increasing protein concn. The inhibition of 7-ethoxycoumarin deethylase by various compounds was investigated; the activity in hairless mouse skin exhibited a greater sensitivity to water-soluble solvents than that in rat skin microsomes. Both hairless mouse and rat skin 7-ethoxycoumarin deethylase were sensitive to inhibition by 5,6-benzoflavone, 7,8-benzoflavone and metyrapone.