INVITRO INTERACTION OF DITHIOCARB WITH RAT-LIVER GLUTATHIONE S-TRANSFERASES

The in vitro interaction of dithiocarb (DTC) [used in the treatment of Wilson''s disease and for nickel carbonyl, arsenic and thallium poisoning] with rat liver glutathione S-transferase [GST] was studied, using reduced glutathione (GSH) and 1-chloro-2,4-dinitrobenzene (CDNB) as substrates. The inhibition of the GST activity by DTC was dose dependent, but not linear. The different GST isoenzymes were inhibited to different degrees. Kinetic studies revealed uncompetitive inhibition towards GSH for GST AA, and an intermediate kinetic pattern between uncompetitive and noncompetitive inhibition for the other GST isoenzymes. With respect to CDNB, mixed type inhibition was found for most GST isoenzymes, and nearly uncompetitive inhibition for GST AA and M. Titration of remaining GSH in appropriate incubation mixtures with DTC revealed no GST catalyzed conjugation of DTC with GSH. Evidently, DTC interacts with GST by direct binding to these proteins. This binding could have a protective function against DTC.