Approaches to in Vivo Enzyme Inhibition: Transition State Analogue Inhibition of Glutathione-S-Transferases by a Meisenheimer Complex

Abstract

A Meisenheimer complex between glutathione and 1,3,5-trinitrobenzene has been shown to function as a relatively strong inhibitor of a glutatione-S-transferase obtained from Galleria mellonella. The associated inhibition constant has been calculated to be 0.17± 0.026 M, which would rank it as one of the stronger inhibitors evaluated to date. Due to the chemical nature of glutathione, which has a pKa of 9.2, the Meisenheimer complex is only formed at pH values about this point. This is evidenced by the decrease in Ki between pH7.5 and pH9.0. Percentage inhibition over a pH range of pH7.0 to pH10.0 indicates that inhibition by the complex begins at pH8.5. This effect is dependent upon glutathione concentrations, since there is a threshold concentration below which 1,3,5-trinitrobenzene would appear to be the major inhibitory species. Using an equilibrium spectrophotometric method the association constant and molar extinction coefficient were calculated as 41.9 1.mol-1 and 20,400 1.mol-1 cm-1 which is similar to those reported in previously published literature.