Glutathione S-transferase isoenzymes and the DDTase activity in two DDT-resistant strains of Aedes aegypti

Abstract

Glutathione S-transferase isoenzymes from 4th instar larvae of two DDT-resistant Aedes aegypti strains were fractionated by anion exchange Q-Sepharose chromatography into GST-2 and a cluster of isoenzymes previously named GST-1. Sequential column chromatography fractionated the GST-1 into at least 6 activity peaks, of which 3 were further purified and named according to the process of purification, GST-1unBPc, GST-1BPa and GST-1BPc. GST-1BPc is confirmed to be one member of the Epsilon class according to the immunological cross-reactivity toward polyclonal antibody against Aedes GSTe2. GST-1unBPc possess the major DDTase activity (>98%) and therefore a play major role on DDT metabolism in the Aedes species. GST-2, which was earlier shown to be over-expressed in DDT-resistance Aedes mosquito, has no DDTase activity, thus the role in DDT resistance may be through sequestration. This report demonstrated that an unknown class, GST-1unBPc, plays a major role in DDT resistance in this species whereas the Epsilon GST-1BPc also contributes to DDT resistance but to a less extent.