Conversion of a Radiolabelled Putative Ecdysone Precursor, 2,22,25-Trideoxyecdysone (5β-Ketodiol) in Larvae and Pupae ofCalliphora vicina

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Abstract
When a tritiated ecdysone precursor, 2,22,25-trideoxyecdysone (5β-ketodiol) was injected into larvae and pupae of Calliphora vicina, it was efficiently converted into 20-hydroxyecdysone. Injections into the anterior and posterior compartments of neck-ligated larvae have shown that both parts can hydroxylate the 5β-ketodiol at C-25, C-22 and C-2 to form ecdysone which was readily hydroxylated at C-20 to form 20-hydroxyecdysone. When incubated with larval brain-ring gland complexes, 5β-ketodiol was converted to ecdysone as well as to other metabolites, such as 22,25-dideoxyecdysone and 2-deoxyecdysone. Other larval tissues, namely the fat body, Malpighian tubules, gut and carcass are also able to transform 5β-ketodiol into ecdysone in vitro, which explains the conversion of the 5β-ketodiol injected into the abdominal portions of neck-ligated larvae. The large tissue distribution of the enzyme systems involved in the terminal hydroxylations of ecdysteroid biosy[ndot]thesis in discussed in view of the results obtained in this and other insect orders.