Ecdysteroid metabolism by soluble enzymes from an insect. Metabolic relationships between 3 beta-hydroxy-, 3 alpha-hydroxy- and 3-oxoecdysteroids.

The formation and fate of 3-dehydroecdysteroids were studied in vitro in tissue extracts from Pieris brassicae (Lepidoptera). Three cytosolic enzymes are involved: an ecdysone oxidase converts 3 beta-hydroxyecdysteroids into 3-dehydroecdysteroids, and two different reductases, requiring NADPH as cofactor, transform 3-dehydroecdysteroids into the 3 alpha-hydroxy- or the 3 beta-hydroxy forms, respectively. 3 alpha-Hydroxyecdysteroid formation is only detected in the gut; all tissues contain the two other activities. It appears that conversion of 3 beta- to 3 alpha-hydroxyecdysteroids proceeds through 3-dehydro compounds. The biological significance of these reactions is discussed.