Studies on the origin of the methylsulfonyl-containing metabolites from propachlor

Metabolites in which the chlorine from propachlor has been replaced by a cysteine group or a methylsulfonyl group [-S(O2) CH3] are present in the urine of rats dosed orally with propachlor. In the present study, urine from rats given single oral doses of 35S-labeled cysteine conjugate of propachlor contained metabolites having the methylsulfonyl groups labeled with 35S. No metabolites containing 14C-labeled methylsulfonyl groups were isolated from urine of rats given single oral doses of the cysteine conjugate of propachlor in which the cysteine group was uniformly labeled with 14C. These findings show that the cysteine conjugate of propachlor is the source of sulfur in the methylsulfonyl-containing metabolites. Therefore, we suggest that a C-S lyase present in the animal cleaves the cysteine conjugate of propachlor and thus allows further metabolism of the sulfur to a methylsulfonyl moiety.