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 character ized in relation to embryonic development. First, subcellular fractions wer e prepared by means of differential centrifugation, and analyzed using mark er enzymes and antibodies against NADPH cytochrome P450 reductase. It was d emonstrated that most ecdysone 20-monooxygenase activity was associated wit h microsomes, and that there was little or no intrinsic mitochondrial ecdys one 20-monooxygenase. Next, conditions for the measurement of ecdysone 20-m onooxygenase activity were established for the microsomal fraction, and cha nges 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 eg gs increased from the gastrula stage. The increase in egg ecdysone 20 monoo xygenase activity was prevented by actinomycin D and alpha-amanitin, sugges ting that gene transcription is required for eliciting an increase in ecdys one 20-monooxygenase activity. Arch. Insect Biochem. Physiol, 41:9-17, 1999 . (C) 1999 Wiley-Liss, Inc.