Characteristics of highly active carboxylesterases in insecticide-resistant Culex pipiens quinquefasciatus

Abstract

Three carboxylesterases (CE's) were separated by PAGE from an organophosphate resistant Culex pipiens quinquefasciatus (Okinawa strain). The first CE was found specifically in the alimentary canal and the second CE distributed throughout the larval body. These CE's were monomeric protein (MW : 60,000) and were categorized as B-type CE. The third CE was a homodimeric protein (MW : ca. 120,000) categorized as A-type CE and detected in all parts except the haemolymph. All CE's showed the characteristic inhibition pattern with organophosphates and carbamates, but their low dissociation constants indicated that the CE's had no hydrolyzing activity against these chemicals. It was supposed from the data presented that the CE's sequestered insecticides and prevented their access to the target, AChE in the central nervous system.