Effect of organophosphate and pyrethroid insecticides on the expression of GSTs from Tenebrio molitor pupae

In the present study we report on the effects of organophosphorous and pyrethroid insecticides on the kinetic properties as well as the isoenzymic profile of the glutathione S-transferase (GST) enzyme system from the pupae stage of the insect Tenebrio molitor. Injection of insecticides into the pupae body had little effect on the kinetic properties of the unpurified enzyme of the surviving insects. Pricking the insects' body wall with a syringe needle without injecting any insecticide caused a decrease of the K-mGSH and V-maxGSH values of the enzyme by threefold. Surprisingly, such a reduction was not observed when insecticide was injected at the same time. Chromatofocusing, revealed that injury alone caused a dramatic decrease in the activity of the alkaline isoenzyme (I), which was not evident when an insecticide was simultaneously injected. According to our results, the alterations of the kinetic characteristics of the unpurified enzyme, observed after injury, are due to an alteration of the isoenzymic profile. Also, injection of a high dose of insecticide results in an increase in the activity of the alkaline isoenzyme, selectively, altering therefore the GST isoenzymic profile of the insect. Our findings may offer an explanation for the controversy that exists in the literature concerning the existence of differences in the kinetic characteristics of the GST enzyme family, between resistant and susceptible insect strains, or before and after treatment with various insecticides. (C) 2000 Academic Press.