Cytosolic glutathione S-transferases in Drosophila melanogaster

Post-microsomal supernatants from Drosophila melanogaster and rat liver homogenates were investigated with respect to their glutathione S-transferase (GST) activity. It appeared that the Drosophila transferase did not conjugate the epoxides styrene-7,8-oxide and 1,2 epoxy-3(p-nitrophenoxy)-propane. Attempts to isolate the Drosophila GST isozymes by means of the well-documented method for the purification of the rat liver transferases failed, because the Drosophila transferases did not bind to CM-cellulose. Purification by subsequent ion exchange on DEAE-cellulose, molecular sieving on Sephadex G-100 and hydroxylapatite chromatography, revealed three active fractions from Drosophila cytosol and five active fractions from rat liver cytosol, using 1-chloro-2,4-dinitrobenzene as the electrophilic substrate. None of the Drosophila active fractions catalyzed the conjugation of glutathione with the epoxides mentioned. It is concluded that there are important differences between the GST systems of both species, resulting in differences in the metabolic fate of chemicals that are substrates for glutathione conjugation. This has to be taken into account in the evaluation of genotoxicity testing in Drosophila of potentially harmful compounds.