Sterol methyl transferase. Evidence for successive C-methyl transfer reactions generating Δ24(28)- and Δ25(27)-olefins by a single plant enzyme
✍ Scribed by Allen L Dennis; W.David Nes
- Book ID
- 104251875
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- French
- Weight
- 191 KB
- Volume
- 43
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
The native SMT from Glycine max (soybean) expressed in Escherichia coli cells catalyzes the step-wise conversion of cycloartenol to 24(28)-methylene cycloartanol to a mixture of stereochemically related D 24(28) Z-ethylidene-D 24(28) E-ethylidene-and D 25(27) -24b-ethylcyclosterols. [27-13 C]Cycloartenol was tested as a substrate to determine the C-25 configuration of the D 24(28) -olefin formed during the first C 1 -transfer reaction. This substrate yielded (25-R)-[27-13 C]24(28)-methylenecycloartanol. These results are entirely consistent with the observed stereochemistries of pathway specific 24-alkyl sterols found in plants and additionally revealed for the first time that a SMT can sequentially C-methylate the D 24 -bond to generate multiple olefins.