Regio- and stereoselectivity of cytochrome P-450 and peroxygenase-dependent formation of cis-12,13-epoxy-9(Z)-octadecenoic acid (vernolic acid) in Euphorbia lagascae.

Two oxygenases associated with microsomes prepared from Euphorbia lagascae developing seeds were found to convert linoleic acid into cis-12,13-epoxy-9(Z)-octadecenoic acid (vernolate): a cytochrome P-450 and a peroxygenase. The cytochrome P-450 dependent epoxidation is characterized by a remarkable regio- and enantioselectivity, i.e. only the 12(S),13(R)-enantiomer is formed in the endosperm. In germinating seeds, peroxygenase was active but no cytochrome P-450 epoxidase could be detected. Moreover, because of the very high enantioselectivity of the fatty acid epoxide hydrolase, which is also found in these tissues and which preferentially hydrates the 12(R),13(S)-epoxide enantiomer, 12(S),13(R)-epoxy-9(Z)-octadecenoic acid is the only isomer which can accumulate in E. lagascae.