S-oxygenation of eptam in hepatic microsomes from fresh- and saltwater striped bass (Morone saxatilis).

The in vitro liver microsomal oxidation of eptam (ethyl N,N-dipropylthiocarbamate) in the presence of freshwater and salt water adapted striped bass liver microsomes was investigated. In freshwater hepatic microsomes from striped bass, eptam is S-oxygenated in a process consistent with the involvement of monooxygenase activity. In contrast, both eptam S-oxide and eptam sulfone are formed in microsomes from salt water adapted striped bass microsomes in a process that is independent of monooxygenase activity and consistent with a role of cooxidation by hydroperoxy fatty acids. The mechanism of oxidation of eptam by hydroperoxy fatty acids may involve radical species. Both eptam S-oxide and eptam sulfone are efficient carbamylating agents toward thiol nucleophiles and react with substituted thiophenols to produce thiocarbamates while eptam itself is relatively stable to trans thiocarbamylation. Monooxygenase-catalyzed S-oxygenation of eptam in freshwater striped bass hepatic microsomes may represent a bioactivation route, which may explain the toxicity of thiocarbamate herbicides such as eptam toward freshwater fish.