ORGANOPHOSPHATE RESISTANCE IN THE TOBACCO APHID (HOMOPTERA, APHIDIDAE) - PURIFICATION AND CHARACTERIZATION OF A RESISTANCE-ASSOCIATED ESTERASE

A 1-naphthyl acetate esterase was identified by isoelectric focusing i n organophosphate resistant (red) tobacco aphids, Myzus nicotianae Bla ckman, which apparently was lacking in susceptible (green) individuals of the same species. This resistance associated esterase (RAE) was pu rified from the cytosol of whole body homogenates of adult tobacco aph ids by gel permeation chromatography and two successive DEAE-Sephacel ion exchange columns. The enzyme eluted from the second DEAE column in 0.23 to 0.28 M NaCl and was approximate to 95% pure as determined by high-performance liquid chromatography (HPLC) on a BIO-SIL TSK-125 col umn. Purified RAE had an apparent molecular weight of 67,300 as determ ined by gel permeation HPLC and 66,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Wide range isoelectric fo cusing (pH 3.5-9.5) on polyacrylamide gel plates indicated that the is oelectric point was 4.61. Rabbit antiserum to the green peach aphid, M . persicae (Sulzer), esterase (E4) specifically cross-reacted with the tobacco aphid RAE, and the two esterases had identical molecular weig hts and isoelectric points as determined by immunoblotting. RAE protei n was not detectable in susceptible tobacco aphids.