Evidence for the involvement of 3-oxo-delta 4 intermediates in ecdysteroid biosynthesis.
Although the involvement of 3-oxo-delta 4 compounds as intermediates in arthropod ecdysteroid biosynthesis has been postulated for a long time, it has not yet been directly demonstrated. In the present study, 3-oxo-delta 4-steroids have been synthesized and incubated in vitro with dissociated moulting gland cells from the crab Carcinus maenas. The tritiated compounds were converted into 3-dehydroecdysone, ecdysone and/or 25-deoxyecdysone, i.e. final ecdysteroids. This means that the 3-oxo-delta 4 compounds had undergone a 5 beta-reduction, to give the 5 beta-conformation of ecdysteroids. Our results suggest that the 3-oxo-delta 4-steroid 4,7-cholestadien-14 alpha-ol-3,6-dione may be an intermediate in the biosynthetic pathway. The 5 beta-reduction reaction involves a cytosolic enzyme which requires NADPH as electron donor and seems specific for 3-oxo-delta 4 substrates. This reaction was the most active in crab Y-organs, as compared with other tissues. The characteristics of the 5 beta-reductase (subcellular localization, substrate and cofactor requirements) appear similar to those of the vertebrate 3-oxo-delta 4-steroid 5 beta-reductase involved in steroid hormone catabolism and bile acid biosynthesis.
Blais
C
C
Ecole Normale Supérieure, Laboratoire de Biochimie, CNRS EP 119, Paris, France.
Dauphin-Villemant
C
C
Kovganko
N
N
Girault
J P
JP
Descoins
C
C
Lafont
R
R
D000818:Animals; D003386:Brachyura / Q000254:growth & development / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D026461:Ecdysteroids; D007301:Insect Hormones / Q000096:biosynthesis* / Q000737:chemistry; D007664:Ketosteroids / Q000138:chemical synthesis / Q000378:metabolism; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011865:Radioisotope Dilution Technique; D013256:Steroids / Q000096:biosynthesis* / Q000737:chemistry; D014316:Tritium
D026461:Ecdysteroids; D007301:Insect Hormones; D007664:Ketosteroids; D013256:Steroids; D014316:Tritium