Glutathione transferase is a mutigene family of enzymes catalyzing the conjugation of glutathione with a large variety of xenobiotics. Glutathione transferase acts on different substrates and can protect insects against various plant allelochemicals and chemical insecticides. An investigation of glutathione transferase in the gut of Palm weevil (Rhynchophorus phoenicis) larva, a lethal pest of palm was carried out. This enzyme was purified to apparent homogeneity after which subunit and native molecular weights of the purified enzyme were determined by denaturing and non-denaturing gel electrophoreses respectively. Some biochemical and kinetic properties of purified glutathione transferase were evaluated. The purified glutathione transferase, a 49.7 kDa protein, showed specific activity of 52.16±5.28 ?mol min-1 mg-1 protein towards its substrate. It showed stable conjugating activity toward its substrates at 30 °C and pH 6.0.The magnitude of activation energy of denaturation (Ed) of this enzyme was 76.86 (KJ/mol).The estimated Michaelis-Menten constants (Km) with respect to 1-chloro-2, 4-dinitrobenzene and glutathione were 0.191±0.03 and 0.136±0.02 mM respectively while the maximum velocity (Vmax) was 46.21±7.23 µmol min-1 ml-1. It was inhibited competitively and non-competitively by divinylphosphate and dimethylphosphate with estimated inhibition constants of KiDVP= 18.23 µM and KiDMP= 88.45 µM respectively. Conclusively, this study established the conjugating activity and some properties of the purified glutathione transferase from the gut of R. phoenicis larva and significance of the results suggest the competence of the larva in handling the biotransformation and removal of chemical assaults. These biochemical properties can be altered for the development of inhibitors with enzymic target for effective pest control.
Keywords: Glutathione transferase, insecticide, purification, R. phoenicis larva, properties, kinetics.