Studies on the black box: Incorporation of 3-oxo-7-dehydrocholesterol into ecdysteroids by Drosophila melanogaster and Manduca sexta

James T. Warren, Michael B. O'Connor, Lawrence I. Gilbert

Research output: Contribution to journalArticlepeer-review

23 Scopus citations

Abstract

It has long been hypothesized that the oxidation of 7-dehydrocholesterol (7dC), made from dietary cholesterol (C), to 3-oxo-7dC (3-oxo-Δ5,7C) immediately precedes the unknown "Black Box" oxidations that lead to the formation of the first up-stream intermediate exhibiting the highly characteristic ecdysteroid structure of the steroid molting hormone of insects, crustaceans and some other arthropods. Perhaps rate-limiting and under the control of the prothoracicotropic hormone (PTTH), the biosynthesis of 3-oxo-7dC and its subsequent oxidative modifications have been difficult to study because of their apparent instability, i.e. no intermediates between 7dC and the diketol (3-oxo-25,22,2-trideoxyecdysone) have ever been observed or identified in insect prothoracic gland incubations with radiolabelled precursors. However, we show that 3-oxo-7dC can be converted into lipophilic, photosensitive, ketone-blocked (PSKB) ketal derivatives which will release 3-oxo-7dC when and where desired following brief irradiation with innocuous long-wave (365 nm) UV-light both in vivo and in vitro. In this manner, 3-oxo-7dC is quickly and efficiently incorporated into ecdysteroids by adult male and female Drosophila raised on a diet containing the PSKB ketals and in prothoracic glands of Manduca sexta incubated with the ketals emulsified into media. The instability of 3-oxo-7dC and its spontaneous transformation into extensively electron-delocalized intermediates will be discussed in relation to a possible mechanism of the Black Box oxidations eventually leading to the production of the active molting hormone 20-hydroxyecdysone (20E).

Original languageEnglish (US)
Pages (from-to)677-687
Number of pages11
JournalInsect Biochemistry and Molecular Biology
Volume39
Issue number10
DOIs
StatePublished - Oct 1 2009
Externally publishedYes

Keywords

  • 20-Hydroxyecdysone
  • 3-Oxo-7-dehydrocholesterol
  • 7-Dehydrocholesterol
  • Black box
  • Cholesta-5,7-diene-3-one
  • Ecdysone
  • Edysteroidogenesis
  • Ketone-blocked ketal intermediates
  • Photosensitive

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