PLANT PHYSIOLOGY , Vol 108, Issue 3 1211-1218, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Characterization of a C-5,13-Cleaving Enzyme of 13(S)-Hydroperoxide of Linolenic Acid by Soybean Seed
Y. P. Salch, M. J. Grove, H. Takamura and H. W. Gardner
United States Department of Agriculture/Agricultural Research Service/National Center for Agricultural Utilization Research, Phytoproducts Research Unit, Peoria, Illinois 61604 (Y.P.S., M.J.G., H.W.G.)
An activity was found in mature soybean seeds (Glycine max L. cv Century)
that cleaved 13(S)-hydroperoxy-9(Z),11(E),15(Z)-octadecatrienoic acid
(13S-HPOT) into 13-oxo-9(Z),11(E)-tridecadienoic acid and two isomeric
pentenols, 2(Z)-penten-1-ol and 1-penten-3-ol. Isomeric pentene dimers were
also produced and were presumably derived from the combination of two
pentene radicals. 13(S)-Hydroperoxy-9(Z),11(E)-octadecadienoic 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 lipoxygenase (LOX) in
the presence of linoleic acid. However, prior to ion-exchange
chromatography, cleavage activity did not require linoleic acid. After
separation by gel filtration followed by ion-exchange chromatography,
cleavage activity was lost but reappeared in the presence of either
linoleic acid or dithiothreitol. Under these conditions cleavage activity
was coincident with the activity of types 1 and 2 LOX. LOX inhibitors
suppressed the cleavage reaction in a manner similar to inhibition of LOX
activity. Heat-generated alkoxyl radicals derived from either 13S-HPOT or
13S-HPOD afforded similar products and yields of
13-oxo-9(Z),11(E)-tridecadienoic acid compared to the enzymic reaction. The
product 1-penten-3-ol may be the precursor of the "raw-bean" volatile
ethylvinylketone.
