Glutathione S-transferase isoenzymes expressed in the three developmental stages of the insect Tenebrio molitor

The isoenzymes of glutathione S-transferase expressed in the three developmental stages [larvae( L), pupae( P), adults( A)] of Tenebrio molitor, an insect of economic significance, were studied. Four major isoenzymes [A (L,P,A), B (L,P,A), C (L,P,A) and D (L,P,A)] were present throughout development as judged by chromatofocusing at pH ranges 7–4 and 9–6. GSTs were purified by means of S-hexyl-GSH-Epoxy activated Sepharose 6B affinity chromatography and subsequent chromatofocusing at pH range 7–4. The molecular weight of the native isoenzymes was estimated to be 50.5 kDa, after gel filtration chromatography, while that of the subunits was 27 kDa, indicating that the enzyme was dimeric. With the exception of the molecular weights which remained constant, the isoelectric points, substrate specificities, sensitivities to inhibitors, pH optima of CDNB-conjugating activity and kinetic parameters of the isoenzymes altered in the three developmental stages.