INVOLVEMENT OF A 3-BETA-HYDROXYSTEROID DEHYDROGENASE-ACTIVITY IN ECDYSTEROID BIOSYNTHESIS

Ecdysteroid biosynthesis was analyzed in vitro using dissociated Y-org an cells from the shore crab Carcinus maenas. 3-Dehydroecdysone (3DE) was detected as a minor secretory product, in addition to the formerly identified end-products 25-deoxyecdysone and ecdysone (E). In convers ion studies, 3DE was formed from tritiated 5 beta-ketodiol (2,22,25-tr ideoxyecdysone), 2,22deoxyecdysone and 2-deoxyecdysone but not from E. Further experiments were performed in order to understand the interco nversions between 3-oxo and 3 beta-OH compounds in the crab Y-organ. T he enzyme involved in 3 beta-dehydrogenation was not ecdysone oxidase, a soluble enzyme found in peripheral tissues of many arthropods but i t presented strong similarities with 3 beta-hydroxysteroid dehydrogena se enzymes from vertebrates: it was membrane-bound and NAD(+)-dependen t. Moreover, a NADH-dependent 3 beta-reduction of several 3-oxo-ecdyst eroids was obtained using the same microsomal fraction (100 000 x g pe llet) of Y-organs, indicating that the reaction might be reversible. A s this activity was specific of molting glands, we hypothesize that th ere is at least one 3 beta-hydroxysteroid dehydrogenase enzyme involve d in the biosynthetic pathway of ecdysteroids. (C) 1997 Elsevier Scien ce Ireland Ltd.