LIPOXYGENASE-CATALYZED OXYGENATION OF LIPIDS

Lipoxygenases (LOXs) and other LOX pathway enzymes are potentially abl e to form a large set of compounds being of commercial interest. Among them are conjugated dienic acids, jasmonates, and volatile aldehydes. Additionally, fatty acid hydroperoxides, formed by LOX, can serve as precursors for further transformation by either enzymes of the so-call ed LOX pathway or by chemical reactions. In the case of linoleic acid more than one hundred products generated from its LOX-derived fatty ac id hydroperoxides have been described. Many of these products exhibit biological activity, suggesting a significant biological function of L OXs. This will be described for two different 13-LOXs. CI) In various oilseeds we found that specific 13-LOXs are localized at the lipid bod y membrane. They are capable of oxygenating esterified polyenoic fatty acids, such as triacylglycerols and phospholipids. In addition, they form with arachidonic acid as substrate preferentially either 8- or Il -hydroperoxy eicosatetraenoic acid, which is a very unusual positional specificity for plant LOXs. (II) From barley leaves we isolated anoth er linoleate 13-LOX form, which is localized within chloroplasts and i s induced by jasmonic acid methyl ester. It is suggested, that this LO X form is capable of oxygenating linolenic acid residues of galactolip ids. Examples will be presented for barley leaves of oxygenated deriva tives of linolenic acid and compounds resulting from the hydroperoxide lyase-branch of the LOX pathway.