INSECT GLUTATHIONE-S-TRANSFERASE - A PREDICTOR OF ALLELOCHEMICAL AND OXIDATIVE STRESS

1. 1. The assay conditions for glutathione-S-transferase (GST) 1-chloro-2,4-dinitrobenzene (CDNB) conjugation and cumene hydroperoxide (cumOOH) reduction were optimized in three lepidopteran insect species. 2. 2. The Km for CDNB was 4.1 × 10-4 M, 7.0 × 10-4 M and 2.1 × 10-3 M for Trichoplusia ni, Spodoptera eridania and Papilio polyxenes, respectively. In that order of insect species, the Km for cumOOH was 2.3 × 10-3 M, 3.8 × 10-3 M and 4.8 × 10-2 M 3. 3. Despite high Kms, the Vmax for both CDNB and cumOOH were high in P. polyxenes, suggesting either a high enzyme concentration or catalytic power represented by the turnover number, Kcat. 4. 4. GST's conjugative activity was in the order of 0.24, 0.09 and 3.19 units in T. ni, S. eridania and P. polyxenes, respectively (1 unit = 1 μmol CDNB conjugated mg protein-1 min-1 at 25°C). 5. 5. The peroxidase activity of GST was high in these insects; 50, 106 and 253 units, respectively, in T. ni, S. eridania and P. polyxenes (1 unit = 1 nmol NADPH oxidized mg protein-1 min-1 at 25°C). 6. 6. The high GST's peroxidase activity apparently remedies the minor activity in these insects of the Se-dependent glutathione peroxidase. © 1990.