Alterations of some glutathione S-transferase characteristics during the development of Tenebrio molitor (Insecta: Coleoptera)

Cytosolic glutathione S-transferase activity was studied in the three developmental stages of Tenebrio molitor. The highest activity towards both CDNB and DCNB was observed in the newly emerged pupae, while towards ethacrynic acid was in the young larvae. The pH optimum of GST activity towards CDNB was 8.5 in larvae and pupae and 8.25 in adults. GSTs operate at a high rate even at pH values 1 or 2 units from their pH optimum. A second lower pH optimum apparently existed in pupae (pH 8). The kinetic parameters (K m and V max) for both GSH and CDNB were determined in the three developmental stages and showed the total amount of GSTs to be elevated in pupae. Three fractions ( not bound, low affinity and high affinity) were obtained after GSH-Epoxy activated Sepharose 6B affinity chromatography of larval homogenate. Chromatofocusing of the fractions, in the pH range 7-4, revealed the presence of four isoenzymes. Changes in kinetic properties and substrate specificities of GSTs during development suggest a differential isoenzymic expression between larval and pupal stages, or alternatively, expression of the same isoenzymes at a different percentage. They also indicate a potentially lower importance of GST detoxification system in the adult stage.