Abstract
Ten cytosolic glutathione S-transferase (GST) isozymes isolated from midguts and fat bodies of control and allelochemical-induced fall armyworm (Spodoptera frugiperda) larvae were tested for their activity toward 13 model substrates belonging to halogenated compounds, nitro compounds,α,β-unsaturated carbonyl compounds, and organic hydroperoxides. Based on the pattern of activity toward these substrates, these GST isozymes exhibited different but overlapping substrate specificities. With a few exceptions, 1-chloro-2,4-dinitrobenzene (CDNB) was the best substrate for these isozymes. The isozymes were active toward numerous toxicα,β-unsaturated carbonyl allelochemicals including trans-2-octenal,trans-2-nonenal, 2,4-hexadienal,trans,trans-2,4-heptadienal,trans,trans-2,4-nonadienal, andtrans,trans-2,4-decadienal, suggesting that GSTs play an important role in the feeding strategies of lepidopterous insects. These GSTs also possessed glutathione peroxidase activity toward cumene hydroperoxide and conjugating activity toward 4-hydroxy nonenal, a lipid peroxidation product, and therefore they are antioxidant enzymes. Microsomal glutathioneS-transferase from fat bodies of fall armyworm larvae metabolized a variety of model substrates such as CDNB, 1,2-dichloro-4-nitrobenzene (DCNB),p-nitrophenyl acetate, and cumene hydroperoxide, but had no activity towardα,β-unsaturated carbonyl compounds. With the exception of ethacrynic acid, glutathioneS-transferase activities toward these substrates were all inducible by allelochemicals such as xanthotoxin and indole 3-acetonitrile in midguts and fat bodies of fall armyworm larvae. Induction ranged from 1.3- to 20.2-fold for midgut GSTs and 1.4- to 48.8-fold for fat body GSTs, depending on the inducer and substrate used. In all instances, DCNB-conjugating activity was most inducible based on percentage of control.© 2002 Elsevier Science (USA)
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