Characterization of the Purified Glutathione S-transferases from Two Psocids Liposcelis bostrychophila and L.entomophila

Glutathione S-transferases(GSTs)from Liposcelis bostrychophila Badonnel and L.entomophila(Enderlein)(Psocoptera:Liposcelididae)were purified by glutathione-agarose affinity chromatography,and characterized subsequently by their Michaelis-Menten kinetics toward the artificial substrates 1-chloro-2,4-dinitrobenzene(CDNB)and reduced glutathione(GSH),respectively.The specific activity of the purified GST toward CDNB was 2.3-fold higher in L.bostrychophila than in L.entomophila.Though the specific activities of purified enzymes varied between the two species,the purification yields were similar.SDS-PAGE revealed one band at 23 kDa for both the species.GSTs of L.entomophila exhibited higher Michaelis-Menten constants(Km)but lower maximal velocity(Vmax)values than those of L.bostrychophila.The optimum pH for CDNB conjugation of L.bostrychophila and L.entomophila GSTs was 7.0 and 7.5,and optimum temperature was35 and 40℃,respectively.Inhibition kinetics showed that cibacron blue,curcumin,bromosulfalein,ethacrynic acid,and carbosulfan had excellent inhibitory effects on GSTs in both species,but the inhibitory effects of beta-cypermethrin,fenpropathrin,tetraethylthiuram disulfide,and diethyl maleate were not significant.