In vitro binding of butyric acid and crotonic acid by the soluble glutathione S-transferases from rat liver.

The in vitro interaction of butyric acid, crotonic acid and n-butylamine with rat liver glutathione S-transferase (GST) was studied, using glutathione (GSH) and 1-chloro-2,4-dinitrobenzene (CDNB) as substrates. Both acids inhibited the GST activity in crude extracts in a dose dependent manner; the amine did not. The GST isoenzymes were inhibited at different degrees. Kinetic studies never revealed competitive inhibition kinetics, with GSH nor with CDNB as the variable substrate. Titration of remaining GSH in appropriate incubation mixtures revealed no GST catalyzed conjugation with GSH. It is concluded that butyric and crotonic acid interact with GST by direct binding to these proteins via their carboxyl group. This binding could have a protective function against these compounds.