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 was 35 and 40°C, 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.