Purification and characterization of glutathione transferases from five phytophagous lepidoptera

Abstract

Glutathione transferases were purified from five species of lepidopterous larvae using a two-step procedure involving ammonium sulfate fractionation and affinity chromatography on a glutathione-agarose column. The highly polyphagous insects, fall armyworm ( Spodoptera frugiperda) and corn earworm ( Heliothis zea), possessed multiple glutathione transferases containing six and four isozymes, respectively. On the other hand, the more specialized insects, tobacco budworm ( Heliothis virescens), cabbage looper ( Trichoplusia ni), and velvetbean caterpillar ( Anticarsia gemmatalis), had a single form of the enzyme. These isozymes consisted of two to four subunits with molecular weights of 27,000 to 32,000, depending on the species. Qualitative differences in glutathione transferase isozymes were observed among these species based on their Michaelis constant, isoelectric point, and relative mobility (electrophoresis). Induction of glutathione transferase in fall armyworm larvae by xanthotoxin increased levels of the existing isozymes but did not result in production of any new isozyme.