Characterization of juvenile hormone hydrolysis in early larval development of Trichoplusia ni

Abstract

AbstractExtensive juvenile hormone (JH) hydrolysis was detected and characterized in whole‐body homogenates of larvae and tissues of Trichoplusia ni during periods of early larval development. The capacity to hydrolyze JH that exists in homogenates of penultimate‐instar larvae is far in excess of the measured hormone levels. The major initial metabolites of JH found in diluted homogenates of early‐instar larvae and larval tissues were JH acid and JH diol as shown by thin‐layer chromatography and microchemical derivatization. Experiments using subcellular fractionation or immunoprecipitation and inhibition studies showed the two hydrolytic activities to be roughly equivalent but located in different subcellular compartments. JH epoxide hydrolase activity was present in the large particle and microsomal fractions, whereas most JH esterase activity was present in the cytosol. Subsequent studies concentrated on JH esterolysis. A titer of JH esterase activity throughout larval development showed this enzyme to be present continuously inside tissues, with periodic manifestations in the hemolymph during each larval molt. Partial purification by affinity chromatography and analysis with sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, Western blotting, and isoelectric focusing showed JH esterase from earlyinstar larvae to be indistinguishable from the enzyme from the last instar. Application of JH II or a juvenoid, Ro 10‐3108, during any time of early larval development caused no apparent abnormalities, suggesting that the action of JH esterase is not involved with elimination of JH during this period. However, application of a JH esterase inhibitor during a critical period of the third to fourth larval molt caused failure of ecdysis, suggesting that JH acid or at least some esterase or protease may be a factor required for the molt.