Comparative studies of ecdysteroid metabolism between diapause eggs and non-diapause eggs of the silkworm, Bombyx mori

2, 22, 25-Trideoxyecdysone (5 beta-ketodiol) has been shown to be derived f rom cholesterol in eggs of the silkworm, Bombyx mori. In order to investiga te the difference in ecdysteroid metabolism between diapause eggs and non-d iapause eggs of the silkworm, H-3-5 beta-ketodiol was microinjected into eg gs at several stages of early embryogenesis, and the metabolites were chara cterized using high-performance liquid chromatography. The injected H-3-5 b eta-ketodiol was metabolized not only to free ecdysteroids, but also to con jugates (phosphoric esters of ecdysteroids), in both diapause eggs and non- diapause eggs. Among these metabolites, 20-hydroxyecdysone, which is consid ered as the active hormone in silkworm eggs, was detected in non-diapause e ggs. However, in diapause eggs, various radioactive putative precursors of 20-hydroxyecdysone, such as 2, 22-dideoxyecdysone, 2-deoxyecdysone and ecdy sone, were detectable, but H-3-20-hydroxyecdysone was not found. These resu lts suggest that the 20-hydroxylation of ecdysone, which is catalyzed by ec dysone 20-monooxygenase, may be a rate-limiting step in the formation of 20 -hydroxyecdysone from ketodiol in the silkworm eggs.