PARTIAL-PURIFICATION AND CHARACTERIZATION OF A GREENBUG (HOMOPTERA, APHIDIDAE) ESTERASE ASSOCIATED WITH RESISTANCE TO PARATHION

Esterases from the greenbug associated with resistance to organophosph ate insecticides were partially purified from both resistant and susce ptible strains by ion-exchange chromatography and preparative electrop horesis. Enzymes from both strains exhibited similar elution profiles although the activity peak from the resistant strain was greater in bo th height and total area. The dominant esterase isozymes from both res istant and susceptible strains were further purified by preparative na tive electrophoresis. Kinetic analysis of the resulting enzyme indicat ed that the K-m of the esterase was identical for the two strains, alt hough V-max was consistently three- five fold higher in the resistant strain. inhibition of the activity from both strains by paraoxon was a lso identical, providing further support for the presence of the same isozyme in the two strains. These results suggest that resistance is a ssociated with overproduction of an isozyme present in the susceptible strain rather than the presence of an enzyme with altered properties. (C) 1994 Academic Press, Inc.