Tissue-Specific Expression of Glutathione Transferase Isozymes in Fall Armyworm Larvae

Abstract

Glutathione transferase (GST) isozymes were purified and isolated from larval midguts and fat bodies of the fall armyworm ( Spodopera frugiperda) using a three-step procedure involving ammonium sulfate fractionation, followed by affinity chromatography on a glutathione-agarose column and nondenaturing polyacrylamide gel electrophoresis. The midgut possessed five isozymes, namely, MG GST-1, MG GST-2, MG GST-3, MG GST-4, and MG GST-5, all of which were heterodimers with subunit molecular weights of 26,700 to 30,000. The p I values ranged from 4.6 to 6.0 among these isozymes. No qualitative difference in isozyme composition was observed during larval development. The fat body contained three isozymes, namely, FB GST-1, FB GST-2, and FB GST-3, all of which were believed to be homodimers with subunit molecular weights of 20,100 to 29,000. The p I values ranged from 4.4 to 6.5 among these isozymes. Using isozyme-specific antisera as probes, MG GST-2, MG GST-3, FB GST-2, and FB GST-3 were found to be immunologically related, possibly due to their sharing of some common subunits. MG GST-2 and MG GST-3 were also immunologically related to the GST from larval Malpighian tubules of fall armyworm. Among the corn earworm, tobacco budworm, beer armyworm, and cabbage looper, MG GST-3 (subunit) was immunologically related to GSTs from all of these species except the cabbage looper, whereas MG GST-2 (subunit) was immunologically related only to the GST from the beet armyworm.