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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 11 ‘‘Heterolytic’’-type hydroperoxide lyase (HPLS) pathway in plant tissues: 9S-<br />

HPOD, 9S-hydroperoxy octodecadienoate; 13S-HPOD, 13S-hydroperoxy octodecadienoate;<br />

9S-HPOT, 9S-hydroperoxy octodecatrienoate; 13S-HPOT, 13S-hyddroperoxy octodecatrienoate.<br />

(Adapted from Ref. 86.)<br />

double bond at C-15 of the allene oxide intermediate appears to facilitate the cyclization<br />

reaction.<br />

The next steps in the pathway to jasmonic acid involve the reduction of the<br />

double bond of cyclopentenone ring of 12-oxo-PDA followed by three successive<br />

�-oxidations [168]. The reduction reaction is catalyzed by 12-oxo-phytodienoate reductase<br />

(EC 1.3.1.42), utilizing NADPH as the reductant to produce (1S,2S)3-oxo-<br />

2(2�-pentenyl)cyclopentaneoctanoic acid (abbreviated OPC-8:0, where 8:0 refers to<br />

the eight-carbon side chain). OPC-8:0 retains the same E stereochemistry of the side<br />

chains as its precursor.<br />

The existence of �-oxidation enzymes in the (�)7-isojasmonic acid pathway<br />

has only been inferred on the basis of the observed products, which are OPC-6:0,<br />

OPC-4:0, <strong>and</strong> OPC-2:0 [(�)7-isojasmonic acid]; no metabolites with odd-numbered<br />

side chains have been identified [169].<br />

Zimmerman [170] was the first to observe that HPDS in flaxseed with tranform<br />

13S-HPOD into 12-oxo-13-hydroxy-9Z-octadecenoic acid (�-ketol). This is the work<br />

that led to the decription of the enzyme as a hydroperoxide isomerase. Zimmerman<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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