PLANT PHYSIOLOGY , Vol 110, Issue 3 807-815, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Peroxygenase-Catalyzed Fatty Acid Epoxidation in Cereal Seeds (Sequential Oxidation of Linoleic Acid into 9(S),12(S),13(S)-Trihydroxy-10(E)-Octadecenoic Acid)
M. Hamberg and G. Hamberg
Department of Medical Biochemistry and Biophysics, Division of Physiological Chemistry II, Karolinska Institutet, S-171 77 Stockholm, Sweden
Peroxygenase-catalyzed epoxidation of oleic acid in preparations of cereal
seeds was investigated. The 105,000g particle fraction of oat (Avena
sativa) seed homogenate showed high peroxygenase activity, i.e. 3034 [plus
or minus] 288 and 2441 [plus or minus] 168 nmol (10 min)-1 mg-1 protein in
two cultivars, whereas the corresponding fraction obtained from barley
(Hordeum vulgare and Hordeum distichum), rye (Secale cereale), and wheat
(Triticum aestivum) showed only weak activity, i.e. 13 to 138 nmol (10
min)-1 mg-1 protein. In subcellular fractions of oat seed homogenate,
peroxygenase specific activity was highest in the 105,000g particle
fraction, whereas lipoxygenase activity was more evenly distributed and
highest in the 105,000g supernatant fraction. Incubation of [1-14C]linoleic
acid with the 105,000g supernatant of oat seed homogenate led to the
formation of several metabolites, i.e. in order of decreasing abundance,
9(S)-hydroxy-10(E),12(Z)-octadecadienoic acid,
9(S),12(S),13(S)-trihydroxy-10(E)-octadecenoic acid,
cis-9,10-epoxy-12(Z)-octadecenoic acid [mainly the 9(R),10(S) enantiomer],
cis-12,13-epoxy-9(Z)-octadecenoic acid [mainly the 12(R),13(S) enantiomer],
threo-12,13-dihydroxy-9(Z)-octadecenoic acid, and
12(R),13(S)-epoxy-9(S)-hydroxy-10(E)-octadecenoic acid. Incubation of
linoleic acid with the 105,000g particle fraction gave a similar, but not
identical, pattern of metabolites. Conversion of linoleic acid into
9(S),12(S),13(S)-trihydroxy-10(E)-octadecenoic acid, a naturally occurring
oxylipin with antifungal properties, took place by a pathway involving
sequential catalysis by lipoxygenase, peroxygenase, and epoxide hydrolase.
