Regulation of sterol biosynthesis in sunflower by 24(R,S),25-epiminolanosterol, a novel C-24 methyl transferase inhibitor

W. David Nes, Giselle G. Janssen, Robert A. Norton, Malgorzata Kalinowska, Farrist G. Crumley, Beni Tal, Annika Bergenstrahle, Lisbeth Jonsson

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Whereas sitosterol and 24(28)-methylene cycloartanol were competitive inhibitors (with Ki=26 μM and 14 μM, respectively), 24(R,S)-25-epiminolanosterol was found to be a potent non-competitive inhibitor (Ki=3.0 nM) of the S-adenosyl-L-methionine-C-24 methyl transferase from sunflower embryos. Because the ground state analog, 24(R,S)-oxidolanosterol, failed to inhibit the catalysis and 25-azalanosterol inhibited the catalysis with a Ki of 30 nM we conclude that the aziridine functions in a manner similar to the azasteriod (Rahier, A., et al., J. Biol. Chem. (1984) 259, 15215) as a transition state analog mimicking the carbonium intermediate found in the normal transmethylation reaction. Additionally, we observed that the aziridine inhibited cycloartenol metabolism (the preferred substrate for transmethylation) in cultured sunflower cells and cell growth.

Original languageEnglish
Pages (from-to)566-574
Number of pages9
JournalBiochemical and Biophysical Research Communications
Issue number1
StatePublished - May 31 1991


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