In vitro interaction of aminobenzenesulfonic acids and their N-acetylated derivatives with rat liver glutathione S-transferase.

The in vitro interaction of the three aminobenzenesulfonic acids sulfanilic-, metanilic- and orthanilic acid, and their N-acetylated derivatives with rat liver glutathione S-transferase (GST) was studied. All inhibited the enzymatic conjugation of 1-chloro-2, 4-dinitro-benzene with glutathione. The sulfonate group and the benzene ring are molecular parts required for this inhibition. Each of the GST isoenzymes (AA, A, B, C, E and M) was inhibited, albeit at different degrees. Kinetic studies always revealed a mixed type function inhibition, towards glutathione and 1-chloro-2,4-dinitrobenzene as well. Conjugates of the six investigated compounds with glutathione were not formed. The results indicate that the aminobenzenesulfonic acids and their N-acetylates interact with GST by direct binding to this protein. It is suggested that the binding to GST of these compounds, from which several are metabolites of colors used in human food, could have a protective function against these dyes.