ON THE MECHANISM OF BIOSYNTHESIS OF DIVINYL ETHER OXYLIPINS BY ENZYMEFROM GARLIC BULBS

The microsomal fraction of homogenate of garlic (Allium sativum L.) bu lbs contains a divinyl ether synthase which catalyzes conversion of (9 Z,11E,13S)-13-hydroperoxy-9,11-octadecadienoic acid and E,13S,15Z)-13- hydroperoxy-9,11,15-octadecatrienoic acid into (9Z,11E,1'E)-12-(1'-hex enyloxy)-9,11-dodecadienoic acid (etheroleic acid) and E,3'Z)-12-(1',3 '-hexadienyloxy)-9,11-dodecadienoic acid (etherolenic acid), respectiv ely. Two isomers of etheroleic acid were isolated. As shown by NMR spe ctrometry, the double bond configurations of these compounds were (9E, 11E,1'E) and (9Z,11Z,1'E). Experiments with linoleic acid (13R,S)-hydr operoxide demonstrated that the S enantiomer was a much better substra te for the divinyl ether synthase compared to the R enantiomer. Incuba tion of 11E,13S)-[O-18(2)]hydroperoxy-9,11-octadecadienoic acid led to the formation of etheroleic acid which retained O-18 in the ether oxy gen. An intermediary role of an epoxyallylic cation in etheroleic acid biosynthesis is postulated.