Inhibition of rat GSH S-transferases by ethylene dibromide

Incubation of ethylene dibromide (EDB) (37 mM) with a mixture of rat hepatic cytosol GSH S-transferases at 25 degrees resulted in diminished activity towards 1-chloro-2,4-dinitrobenzene (CDNB) and 3,4-dichloronitrobenzene (DCNB). The loss of both activities followed pseudo first order kinetics with a rate constant of 0.13 +/- 0.03 min-1. The concentration of EDB required for half maximal loss of enzymic activity towards CDNB was 3.2 mM. Removal of EDB from the enzyme by lyophilization or gel filtration did not result in the return of activity towards CDNB. GSH partially prevented the loss of activity, but could not reverse the loss. EDB decreased the activity of forms A(YbYb) and C(YbYb) of rat liver GSH S-transferases but not of forms AA(YcYc), B(YaYc) or B(YaYa). It is concluded that EDB inhibits forms A and C of the GSH S-transferases via a mechanism not involving suicide inhibition.