CONVERSION OF DIFFERENT PUTATIVE ECDYSTEROID PRECURSORS IN LITHOBIUS-FORFICATUS L (MYRIAPODA, CHILOPODA)

The biosynthetic pathway of ecdysteroids has been investigated in the centipede Lithobius forficatus. By using various labeled putative prec ursors already known to be efficiently converted into ecdysone and 20- hydroxyecdysone by insects and crustaceans, it was found that the reac tions always stopped at 2-deoxyecdysone, and that this compound was on ly epimerized and conjugated at the C-3 position. Ecdysone was efficie ntly converted into 20-hydroxyecdysone, whereas 20-hydroxylation was n ot effective with 2-deoxyecdysteroids. None of the tested precursors w as hydroxylated at the C-2 position. In addition, in vivo labeling exp eriments with [H-3]cholesterol led only to the formation of unidentifi ed products. Therefore, the origin of the already reported ecdysone an d 20-hydroxyecdysone in these animals remains still conjectural. The ' 'ecdysial glands'' (i.e. the putative molting glands) and gonads prove d the most effective tissues to convert 2,22,25-trideoxyecdysone into 2-deoxyecdysone in vitro, although at rather low levels. By contrast, this compound was very efficiently converted in vivo. The present data raise many unanswered questions, and they point out that classical in sect schemes are not applicable in the present case. It might thus wel l be that divergent pathways have evolved in arthropods, and this prob lem awaits further investigations.