Pharmacokinetic studies of the recombinant juvenile hormone esterase in Manduca sexta

Abstract

Catalytically active juvenile hormone esterase (JHE) was expressed at a high level by Spodoptera frugiperda cells infected with recombinant Autographa californica nuclear polyhedrosis virus carrying the JHE gene cloned from the tobacco budworm, Heliothis virescens. JHE was partially purified from the culture medium by DEAE ion-exchange chromatography to a specific activity of 3000–5200 nmol juvenile hormone III metabolized per minute per milligram of protein after viral particles were inactivated by Triton X-100 following ultracentrifugation. Pharmacokinetic studies showed that catalytic activity was cleared with first-order kinetics after the purified enzyme was injected into larval hemolymph of the tobacco hornworm, Manduca sexta and H. virescens. The half-life of JHE was approximately 1.2 hr in both species. Experiments were undertaken to elucidate the mechanism of clearance from M. sexta larvae. Persistence of catalytic activity in hemolymph in vitro and Western blot analysis suggested an uptake process of JHE by tissue(s), rather than degradation in the plasma. Injection of a high dose of JHE resulted in an increased half-life and showed that the clearance process was saturable. The clearance rate was decreased by coinjection of a high dose of JHE inactivated by an irreversible inhibitor, paraoxon. Coinjection of an equal amount of bovine serum albumin did not influence the clearance rate of JHE. These results suggest that a specific process is involved in JHE clearance from hemolymph. N-linked oligosaccharides of JHE apparently were not important in the clearance of JHE from hemolymph.