Ecdysone 20-hydroxylation in imaginal wing discs of Pieris brassicae (lepidoptera): Correlations with ecdysone and 20-hydroxyecdysone titers in pupae

Ecdysone 20-hydroxylase activity has been detected in pupal wing discs of Pieris brassicae. This activity is due to an enzyme system located in microsomal fractions. Its apparent Km is 58 nM for ecdysone. The enzyme is inhibited by the reaction product 20-hydroxyecdysone with an apparent Ki of 2.6 μM. Its activity varied during pupal-adult development with a maximum on day 4, when ecdysone levels are the highest in the animal. Although low, the peak activity is sufficient to assure 25% of the conversion of endogenous ecdysone into 20-hydroxyecdysone in pupae. Ecdysone and 20-hydroxyecdysone levels were measured in hemolymph and whole animals; ecdysone appears to be mainly located in hemolymph, whereas 20-hydroxyecdysone seems to be equally distributed between hemolymph and tissues. All these findings are discussed in relation to the roles of ecdysone and 20-hydroxyecdysone during pupal-adult development.