Interaction of benzo- and naphthoquinones with soluble glutathione S-transferases from rat liver.

The in vitro interaction of 1,4-benzoquinone, 1,2- and 1,4-naphthoquinone, and 2-methyl-1,4-naphthoquinone with rat liver glutathione S-transferases (GST) was studied, using reduced glutathione and 1-chloro-2,4-dinitrobenzene (CDNB) as substrates. The inhibition of the GST activity by quinones in crude extracts was dose dependent. While most of the dihydroxynaphtalenes investigated also inhibited the GST activity, dihydroxybenzenes and catecholamines did not. The quinones inhibited all the GST isoenzymes, albeit at different degrees. Kinetic studies revealed mixed type function inhibition towards glutathione and competitive inhibition towards CDNB, implicating that quinones are GST substrates. This was further confirmed by titration of remaining glutathione in appropriate incubation mixtures. These results indicate that GST could have a protective function against quinones, and that catecholamines are conjugated with glutathione via a reactive quinone intermediate.