Cycloeucalenol: obtusifoliol isomerase

Rahier, A., Taton, M. and Benveniste, P. (1989) Cycloeucalenol-obtusifoliol isomerase. Structural requirements for transformation or binding of substrates and inhibitors. Eur. J. Biochem., 181,615-26. 

The next question is when in the biosynthetic pathway do the two methylations take place. As already indicated, experiments with enzyme preparations demonstrate that cycloartenol is the best substrate for the first methylation. However 24-methylene lophenol (5-F) and not 24-methylene cycloartanol (2-F), is the preferred substrate for the second methylation. This is formed by the pathway indicated in Fig. 8. 24-Methylene cycloartanol (2-F) is demethylated to cycloeucalenol (8-F) which is the substrate for cycloeucalenol obtusifoliol isomerase which opens the 9,19-cyclopropane ring to form obtusifoliol (13-F) demethylation at C-14 and isomerization... 

Microsomal extracts from maize seedlings are capable of catalyzing the alkylation of cycloartenol (3) by 5-adenosyl-methionine to produce 24-methylenecycloartenol (Fig. 23.11) (Harrison, 1988). The enzymes involved in transformations of cycloeucalenol (19) to obtusifoliol (18) (cycloeucalenol obtusifoliol isomerase), obtusifoliol to 4a-methyl-ergosta-8,14,24(28)-trien-3p-ol (20) (14a-methylsterol... 

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