Inhibition of octopus glutathione transferase by Meisenheimer complex analog, S-(2,4,6-trinitrophenyl) glutathione

The tight binding of Meisenheimer intermediate with octopus digestive gland glutathione transferase was analyzed with 1,3,5-trinitrobenzene, which for ms a trapped Meisenheimer complex with glutathione because there is no leav ing group at the ipso carbon. By steady-state enzyme kinetic analysis, an i nhibition constant of 1.89 +/- 0.17 muM was found for the transient formed, S-(2,4,6-trinitrophenyl) glutathione. The above inhibition constant is 407 -fold smaller than the K-m value for the substrate (2,4-dinitrochlorobenzen e). Thus, S-(2,4,6-trinitrophenyl) glutathione is considered to be a transi tion-state analog. The tight binding of this inhibitor to the enzyme provid es an explanation for the involvement of the biological binding effect on t he rate enhancement in the glutathione transferase-catalyzed SNAr mechanism .