Many workers have reportedenzymatic determination of pesticides. GUILBAULT AND Kn~arERl~2
used both lipase and cholinesterase enzymes to determine very low concentrations of certain pesticides. GIASG AND HALLS used acetylcholine chloride as substrate for cholinesterase to measure the percentage inhibition by organophosphorus insecticides. Although the;e papers and many more provide sensitive methods of analysis, the major emphasis has been on organophospl~orus compounds. Moreover, these methods lack specificity. GUILBAULT et al. 294, have already reported inhibition of Iipase by chlorinated insecticides such as Aldrin, Lindane, Heptachlor, DDT, and a carbamate, Sevin. A sensitive method for analysis of all the above-mentioned insecticides in addition to bismuth, beryllium and Metllylparatllion, has been proposedJ. Unfortunately, these methods are of limited use because of a lack of specificity. Since it is known that various animals and insects respond in different ways to different insecticides or pesticides, it seemed desirable to isolate a more purified enzyme from different sources for studying their inhibition by different pesticides. With these facts in mind, inhibitory studies of partially purified cholinesterases from housefly (DDT-resistant), housefly (NAIDM), sugar boll weevil, fire ant and German cockroaches, by various pesticides were conducted.
EXPEIUICIENTAL
Substrate. N-Methylindoxyl
acetate (Isolab, Inc., Drawer 4350, Akron, Ohio). A x0-2 M solution (x.91 mg ml-r) was prepared in methyl cellosolve.
Pesticides. Stock solutions or various concentrations were prepared in dioxanc. The pesticides were all gg+ oh purity and were all obtained from Polyscience Corp., Evanston, Illinois, except for Paraoxon which was obtained from American Cyanamid Co. (Bound Brook, N. J.). The Paraoxon content of Parathion was assayed by i.r. spectroscopy (P + 0 bond) and thin-layer chromato@aphy, and was found to be about ~01~.
Buffws.
0.x M Phosphate buffer was prepared by dissolving sodium dihydrogen phosphate in triply distilled water. The pH was adjusted to 7.0 with sodium hydroxide.
Measwemmt of enzyme activity.
Cholinesterase activity of different preparations .4,tal. Cl1im. Acta, 52 (1970)