A novel glutathione conjugation of the organophosphorus insecticide prothiofos by the housefly abdomen glutathione S-transferase 6B

The cloning of glutathione S-transferase (GST) 6A and 6B genes in the susceptible and resistant houseflies (Takatsuki and Yachiyo strains) and the expression of their genes in Escherichia coli were carried out to obtain the GST6A and 6B enzymes. Similarly to the housefly abdomen GST 6A enzymes, the housefly abdomen GST6B enzymes conjugated alkyl group on phosphorus atom of prothiophos oxon with glutathione. However, the GST6B enzyme derived from the resistant housefly had only 1/2 level of GST activity for the above GSH conjugation reaction, compared with the GST6 B derived from the susceptible housefly, to decrease the ability in detoxification. On the other hand, in vitro oxidative GSH conjugation reaction indicated that their GST6B enzymes cover a novel GSH conjugation reaction at least. The reaction of prothiohos oxon S-oxide with GSH was predicted on computational chemistry using BioMedCAChe software. One was SN2 reaction of GSE- to phosphorus atom, and the other was SN2 reacion of GSE- to methylene carbon atom of ethoxyl group. The GST6 B enzyme probably plays an important role in the control of resistant decrease for houseflies.