The production of an esterase inhibitor from schradan in the fat body of the desert locust

Abstract

The capacity of the fat body of the desert locust to convert schradan into an esterase inhibitor is high in young fifth-instar nymphs, but falls sharply before the final moult. The conversion requires O2 reduced triphosphopyridine nucleotide and a particle-bound enzyme system. It is inhibited by chelating agents (reversibly) and by mepacrine, [rho]-chloromercuribenzoate and 2,4-dinitro-phenol. No requirement for a metal or flavine prosthetic group could be shown with the particle-bound system. A Fe++ ion-ethylenediaminetetra-acetic acid complex can catalyze the oxidative formation of an inhibitor from schradan. A mechanism for the simultaneous oxidation of schradan and reduced triphosphopyridine nucleotide is suggested. The requirements for the conversion of dimefox to an anti-esterase are the same as those for schraden, but the rate of the esterase inhibition is much higher. Dimefox is also considerably more toxic than schradan to the locust, but LD50 does not vary with fat-body converting activity.