HYDROXYLATION AND N-DEMETHYLATION OF CHLOROTOLURON BY WHEAT MICROSOMAL-ENZYMES

In vitro metabolism of the herbicide chlorotoluron was studied in various subcellular fractions from suspension-cultured cells of wheat (Triticum aestivum) treated with cyometrinil. The highest rates of degradation of herbicide were found in microsomal fractions exhibiting a NADPH-cytochrome P-450 (cytochrome c) reductase activity. Membrane fractions supported the ring-methyl hydroxylation and the first N-demethylation of chlorotoluron in the presence of molecular oxygen and NADPH. Cell treatment by cyometrinil increased the rates of these two reactions, the activity of lauric acid in-chain hydroxylase and the levels of cytochromes P-450. Ring-methyl hydroxylation and N-demethylation of chlorotoluron were drastically reduced by para-chloromercuribenzoate and by compounds draining electrons from NADPH-cytochrome P-450 (cytochrome c) reductase. Ring-methyl hydroxylase was also strongly inhibited by CO, with partial reversion by light. Combination of these data allow to postulate that ring-methyl hydroxylase of wheat belongs to the family of cytochrome P-450 monooxygenases. In contrast, the N-monodemethylated metabolite could also be formed in the presence of cumene hydroperoxide, and the N-demethylase activity was not affected by CO. These distinctive properties still raise some questions about the nature of the monooxygenase(s) involved in the first N-demethylation of chlorotoluron in wheat cells. © 1990.