A comparison of the induced and naturally occurring juvenile hormone esterases from last instar larvae of Trichoplusia ni

Abstract

During the last larval instar of Trichoplusia ni two naturally occurring peaks of juvenile hormone esterase activity are present. After a critical period, juvenile hormone esterase activity can be induced in normal and ligated larvae by the topical application of juvenile hormone or juvenoids. The natural and artificially induced juvenile hormone esterases are similarly inhibited by a selected group of organophosphate and carbamate inhibitors. Paraoxon and O- ethyl-S- phenyl phosphoramidothiolate displayed the best inhibition, both with an I 50 of 1 × 10 −6M, while several general esterase inhibitors, including diisopropyl phosphorofluoridate, had very little effect. The three groups of juvenile hormone esterases have similiar gel filtration patterns which are distinct from most of the α-naphthyl acetate esterase activity. The natural and artificially induced juvenile hormone esterases demonstrated identical migration patterns when analyzed by gel electrophoresis. Isoelectric focusing also resulted in essentially identical activity patterns and pI values for each of the three groups of juvenile hormone esterases. Both naturally occurring peaks of juvenile hormone esterase activity as well as an artificially induced peak of juvenile hormone esterase activity appear to be largely due to one enzyme, and within the limits of the techniques used, these esterases are identical. The juvenile hormone esterase activity is distinct from and more stable than the majority of the α-naphthyl acetate esterase activity in the haemolymph.