In vitro interaction of organic mercury compounds with soluble glutathione S-transferases from rat liver

The in vitro interaction of organic mercury compounds with rat liver glutathione S-transferases (GST) was studied, using reduced glutathione (GSH) and 1-chloro-2,4-dinitrobenzene (CDNB) as substrates. The inhibition of the GST activity was dose dependent, but not linear. The different GST isoenzymes were inhibited to different degrees. Kinetic studies never revealed competitive inhibition, with CDNB or with GSH as the variable substrate. Titration of remaining GSH in appropriate incubation mixtures with organomercurials revealed no GST catalyzed conjugation of these compounds with GSH. These experiments showed a spontaneous conjugation of the mercury compounds with GSH, explaining the parabolic inhibition observed in the kinetic studies with GSH as the variable substrate. Both organic and inorganic mercury are spontaneously conjugated with GSH, but interact with GST by direct binding to these proteins. This binding could have a protective function against mercury. No qualitative differences between organic and inorganic mercury were detected.