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Insect Glutathione S-transferases and detoxification of plant chemicals, D3, Tran Thi Thu Phuong

2014/12/15 19:22 に ユーザー不明 が投稿

Glutathione S-transferases (GSTs) are a diverse family of enzymes, which play an important role in the detoxification of both endogenous and xenobiotic compounds in insect. GSTs primarily catalyse the conjugation of electrophilic compounds with the thiol group of reduced glutathione (GSH), generally making the resultant products more water soluble and excretable than the non-GSH conjugated substrates. GSTs are classified according to their location within the cell into microsomal and cytosolic, depending on their localization in the cell. Most insect GSTs are cytosolic and present in both homo and heterodimeric forms with subunit masses of approximately 25 kDa. Insect GSTs are classified into six major subclasses, including Sigma, Omega, Zeta, Theta, and insect specific Delta and Epsilon (Enayati et al., 2005; Friedman 2011). A number of insect cytosolic GSTs were identified, such as 38 in Drosophila melanogaster, 23 in Bombyx mori, 28 in Anopheles gambiae, 26 in Aedes aegypti, 18 in Acyrthosiphon pisum, and 11 in Apis mellifera (Enayati et al., 2005; Friedman, 2011; Yu et al., 2008).

GST activity in different insect tissues were reported in some species. It is believed that the high levels of GST activity in the fat body and midgut of insect are important for the detoxification of plant allelochimical (Enayati et al., 2005). For instance, GSTs of Spodoptera litura were observed higher expression levels in the larval stages than in other stages and their expression levels in the midgut were higher than in other tissues. The expression of GST such as SlGSTe1, SlGSTe3, SlGSTs1, SlGSTs3 and SlGSTo1 were increased by xanthotoxin, a secondary metabolite form Apiaceae (Huang et al., 2011). In larval Agrilus planipennis, GSTs in midgut and malpighian tubeles might play an essential role in detoxification to metabolize ash allelochemicals (Rajarapu & Mittapalli, 2013). Similarity, the activity of GST in midgut wall of Poecilocerus bufonius was significantly higher after 24 hours of feeding on the main host plant Calotropis procera containing Cardenolids (Elsayed et al., 2012).

In the other hand, GSTs also play a central role in insecticide resistance in insect such as Locusta migratoria and Anopheles gambiae (Enayati et al., 2005; Qin et al., 2013). In Locusta migratoria, the maximum expression of GSTs proteins (LmGSTd1, LmGSTs5, LmGSTt1, and LmGStu1) was observed in malpighian tubules and fat bodies, and high expression in midgut. Sigma GSTs in L. migratoria play a major role in carbaryl detoxification, while other GSTs were reported that involve in the chlorpyrifos detoxification (Qin et al., 2013). In addition, GST enzymes in houseflies and the mosquito A. gambiae catalyzed for dehydrochlorination which is an important mechanism for DDT detoxification (Enayati et al., 2005).

In conclusion, GSTs are important detoxifying enzymes in insect. GSTs act on different substrates and can detoxify several plant allelochemicals and chemical insecticides. GSTs have high expression in midgut, fat body and malpighian tubules which detoxified the toxic compounds in insect body.



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