ENVELOPE MEMBRANES FROM SPINACH-CHLOROPLASTS ARE A SITE OF METABOLISMOF FATTY-ACID HYDROPEROXIDES

Enzymes in envelope membranes from spinach (Spinacia oleracea L.) chlo roplasts were found to catalyze the rapid breakdown of fatty acid hydr operoxides. In contrast, no such activities were detected in the strom a or in thylakoids. In preparations of envelope membranes, 9S-hydroper ox-10(E),12(Z)-octadecadienoic acid, 13S-hydroperoxy-9(Z),11 (E)-octad ecadienoic acid, or 13S-hydroperoxy-9(Z),11(E), 15(Z)-octadecatrienoic acid were transformed at almost the same rates (1-2 mu mol min(-1) mg (-1) protein). The products formed were separated by reversed-phase hi gh-pressure liquid chromatography and further characterized by gas chr omatography-mass spectrometry. Fatty acid hydroperoxides were cleaved (a) into aldehydes and oxoacid fragments, corresponding to the functio ning of a hydroperoxide lyase, (b) into ketols that were spontaneously formed from allene oxide synthesized by a hydroperoxide dehydratase, (c) into hydroxy compounds synthesized enzymatically by a system that has not yet been characterized, and (d) into oxoenes resulting from th e hydroperoxidase activity of a lipoxygenase. Chloroplast envelope mem branes therefore contain a whole set of enzymes that catalyze the synt hesis of a variety of fatty acid derivatives, some of which may act as regulatory molecules. The results presented demonstrate a new role fo r the plastid envelope within the plant cell.