METABOLISM OF JUVENILE-HORMONE BY THE EPIDERMIS OF THE TOBACCO HORNWORM, MANDUCA-SEXTA

The dorsal abdominal epidermis of the last (fifth) instar larvae of the tobacco hornworm, Manduca sexta, was found to convert juvenile hormone I (JH) primarily into JH-acid with the acid-diol comprising less than 10% of the metabolites. This esterase activity of the epidermis increased as a function of larval age, the t 1 2 for JH in the medium being 45, 21, and 7 min for day 1, day 2, and day 3 larvae respectively. Since the increased esterase activity of the epidermis was not inhibited by DFP and paralleled the increase found in the haemolymph, it was considered to be a 'JH-specific' esterase(s) and likely to be involved in elimination of intracellular JH from the target tissues in preparation for metamorphosis. The JH-binding protein tripled the half-life of JH in the medium, irrespective of the age of the epidermis, apparently by retarding its uptake. In spite of this protection of JH from degradation, the presence of the JH-binding protein had no significant influence on the action of JH in the prevention of the 20-hydroxyecdysone induced change of commitment of the epidermis. © 1979.