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| The toxicological and biochemical characteristics of glutathione S-transferases (GSTs) in the resistant and susceptible strains of Liposcelis bostrychophila were investigated. Compared to their susceptible counterparts, the activities per insect and specific activities of GSTs in the DDVP- and PH3- resistant strains (DDVP-R and PH3-R) were significantly higher. The apparent Michaelis-Menten constant ( Km ) for CDNB were obviously lower in DDVP-R and PH3-R (i.e. lower Km values, 1.5625 mM for DDVP-R and 0.6230 mM for PH3-R) as compared with their susceptible counterpart (Km=3.5520), indicating a higher affinity to the substrate CDNB in resistant strains. In contrast, the catalytic activity of GSTs towards CDNB in susceptible strain was significantly higher than those in resistant strains. It was noticeable that when GSH used as substrate, GSTs from resistant strains both indicated a significantly declined affinity. For the catalytic activity of GSTs towards GSH, only the Vmax value in DDVP-R increased significantly compared to that from susceptible strain, suggesting an over expression of GST in this resistant strain. The inhibition kinetics of insecticides to GSTs in vitro revealed that dichlorvos and paraoxon possessed excellent inhibition effects on GSTs. The susceptible strain showed higher sensitivity (I50=0.9004 mM) to dichlorvos than DDVP-R and PH3-R (higher I50s, 8.0955 mM for DDVP-R and 9.3346 mM for PH3-R). As for paraoxon, there was a similar situation. The resistant strains both suggested a higher I50 (1.8735 mM for DDVP-R, and 0.4291 for PH3-R) compared to the susceptible strain (0.2943 mM). These suggested that an elevated detoxification ability of GSTs developed in the resistant strains. |
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| Keywords:Liposcelis bostrychophila, GSTs, resistance |
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