CHARACTERIZATION OF A C-5,13-CLEAVING ENZYME OF 13(S)-HYDROPEROXIDE OF LINOLENIC ACID BY SOYBEAN SEED

An activity was found in mature soybean seeds (Glycine max L. cv Centu ry) that cleaved 3(S)-hydroperoxy-9(Z),11(E),15(Z)-octadecatrienoic ac id (13S-HPOT) into 13-oxo-9(Z),11 (E)-tridecadienoic acid and two isom eric pentenols, 2(Z)-penten-1-ol and 1-penten-3-ol. Isomeric pentene d imers were also produced and were presumably derived from the combinat ion of two pentene radicals. 13(S)-Hydroperoxy-9(Z),11(E)-octadecadien oic acid (13S-HPOD) was, by contrast, a poor substrate. Activity with 13S-HPOT increased 24-fold under anaerobic conditions reminiscent of a similar anaerobic promoted reaction of 13S-HPOD catalyzed by lipoxyge nase (LOX) in the presence of linoleic acid. However, prior to ion-exc hange chromatography, cleavage activity did not require linoleic acid. After separation by gel filtration followed by ion-exchange chromatog raphy, cleavage activity was lost but reappeared in the presence of ei ther linoleic acid or dithiothreitol. Under these conditions cleavage activity was coincident with the activity of types 1 and 2 LOX. LOX in hibitors suppressed the cleavage reaction in a manner similar to inhib ition of LOX activity. Heat-generated alkoxyl radicals derived from ei ther 13S-HPOT or 13S-HPOD afforded similar products and yields of 13-o xo-9(Z),11 (E)-tridecadienoic acid compared to the enzymic reaction. T he product 1-penten-3-ol may be the precursor of the ''raw-bean'' vola tile ethylvinylketone.