Effect of inhibitors on ω-and (ω-1)-hydroxylation of lauric acid by frog liver microsomes

To investigate the involvement of different cytochrome P-450 monooxygenases in fatty acid hydroxylation in frog liver microsomes, the effect of various inhibitors of cytochrome P-450 monooxygenases on the ω- and (ω-1)-hydroxylation of laurate was examined. The ω/ω-1-hydroxylation ratios were changed significantly by various levels of carbon monooxide (CO) inhibition; the formation of ω-hydroxylaurate was more sharply inhibited by various levels of CO than was the formation of (ω-1)-hydroxylaurate. On the contrary, metyrapone inhibited only the formation of (ω-1)-hydroxylaurate and stimulated the formation of ω-hydroxylaurate. 7,8-Benzoflavone as well as CO was more inhibitory to the ω-hydroxylation of laurate. At low concentrations of KCN (0.2 and 0.1 mM), the (ω-1)-hydroxylase activity was stimulated, but both the ω- and (ω-1)-hydroxylase activities were inhibited at the higher concentrations (5–10 mM). The effect of drugs and hydroxylaurate isomers on the ω- and (ω-1)-hydroxylation was also examined. Aminopyrine showed a stimulative effect on ω-hydroxylase activity and no effect on the (ω-1)-hydroxylase activity, whilep-nitroanisole inhibited the (ω-1)-hydroxylase activity and showed almost no effect on the ω-hydroxylase activity. 12-Hydroxylaurate inhibited both the ω- and (ω-1)-hydroxylase activities, but the ω-hydroxylase activity was inhibited to a much greater extent. 11-Hydroxylaurate had no effect on either hydroxylation. These findings strongly support the hypothesis that different cytochrome P-450 species are involved in the hepatic microsomal hydroxylation of laurate at ω- and (ω-1)-positions in the frog.