Ecdysone 20-monooxygenase in eggs of the silkworm, Bombyx mori: enzymatic properties and developmental changes

Ecdysone 20-monooxygenase in eggs of the silkworm Bombyx mori was characterized in relation to embryonic development. First, subcellular fractions were prepared by means of differential centrifugation, and analyzed using marker enzymes and antibodies against NADPH-cytochrome P450 reductase. It was demonstrated that most ecdysone 20-monooxygenase activity was associated with microsomes, and that there was little or no intrinsic mitochondrial ecdysone 20-monooxygenase. Next, conditions for the measurement of ecdysone 20-monooxygenase activity were established for the microsomal fraction, and changes in the enzyme activity were measured in diapause eggs and non-diapause eggs during early embryogenesis. It was demonstrated that enzyme activity in diapause eggs remained at a low level, while that in the non-diapause eggs increased from the gastrula stage. The increase in egg ecdysone 20-monooxygenase activity was prevented by actinomycin D and alpha-amanitin, suggesting that gene transcription is required for eliciting an increase in ecdysone 20-monooxygenase activity.