Abstract
Two approaches were taken to identify and characterise the juvenile hormone esterase (JHE) of Drosophila melanogaster. The first investigated the properties of an esterase denoted EST20, which can be visualised on a native polyacrylamide gel using an in vitro esterase, naphthylacetate. D. melanogaster EST20 is likely to be a homologue of the p-esterase of D. virilis which has been claimed to be JHE. However, we show here that juvenile hormone (JH) hydrolytic activity is not associated with either EST20 in D. melanogaster or the p-esterase in D. virilis. The second approach used a direct radiometric assay of JH-hydrolysing activity. Hydrolytic activity measured in this way was recovered after native PAGE of D. melanogaster pupae did not correspond to any of the naphthylacetate staining esterases. The developmental profile of JH-hydrolytic activity in D. melanogaster correlates inversely with JH titre and closely resembles the lepidopteran profile. Two JH-hydrolysing enzymes were identified; JHE and juvenile hormone epoxide hydrolase (JHEH). The largest peak of JHE activity is soluble and coincides with pupation. Lower JHE activity is found in adult microsomes, together with JHEH activity. JH-hydrolytic activity in larvae is largely due to JHEH. JHEs from D. melanogaster and D. virilis are sensitive to inhibition by the esterase inhibitor OTFP, and, in contrast to lepidopterans, are also sensitive to DFP.
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