Efficient and Specific Conversion of 9-Lipoxygenase Hydroperoxides in the Beetroot. Formation of Pinellic Acid

The linoleate 9-lipoxygenase product 9(S)-hydroperoxy-10(E),12(Z)-octadecadienoic acid was stirred with a crude enzyme preparation from the beetroot (Beta vulgaris ssp. vulgaris var. vulgaris) to afford a product consisting of 95% of 9(S),12(S),13(S)-trihydroxy-10(E)-octadecenoic acid (pinellic acid). The linolenic acid-derived hydroperoxide 9(S)-hydroperoxy-10(E),12(Z),15(Z)-octadecatrienoic acid was converted in an analogous way into 9(S),12(S),13(S)-trihydroxy-10(E),15(Z)-octadecadienoic acid (fulgidic acid). On the other hand, the 13-lipoxygenase-generated hydroperoxides of linoleic or linolenic acids failed to produce significant amounts of trihydroxy acids. Short-time incubation of 9(S)-hydroperoxy-10(E),12(Z)-octadecadienoic acid afforded the epoxy alcohol 12(R),13(S)-epoxy-9(S)-hydroxy-10(E)-octadecenoic acid as the main product indicating the sequence 9-hydroperoxide → epoxy alcohol → trihydroxy acid catalyzed by epoxy alcohol synthase and epoxide hydrolase activities, respectively. The high capacity of the enzyme system detected in beetroot combined with a simple isolation protocol made possible by the low amounts of endogenous lipids in the enzyme preparation offered an easy access to pinellic and fulgidic acids for use in biological and medical studies.