Metabolism of Linoleic Acid by Barley Lipoxygenase and Hydroperoxide Isomerase

Abstract

The oxidation of linoleic acid in incubation mixtures containing extracts of barley lipoxygenase and hydroperoxide isomerase, and the production of these enzymes in quiescent and germinated barley, were investigated.The ratio of 9-hydroperoxylinoleic acid to 13-hydroperoxylinoleic acid was higher for incubation mixtures contain extracts of quiescent barley than for mixtures containing extracts of germinated barley, production of 13-hydroperoxylinoleic acid from germinated barley exceeded that of quiescent barley. Hydroperoxy metabolites of linoleic acid were converted to 9-hydroxy-1O-oxo-cis-12-octadecenoic acid, 13-hydroxy-10-oxo-tr-11-octadecenoic acid, and small amounts of 11-hydroxy-12,13-epoxy-cis-9-octadecenoic acid and 11-hydroxy-9,10-epoxy-cis-13-octadecenoic acid whether quiescent or germinated barley was the enzyme source; a fifth product, 13-hydroxy-12-oxo-cis-9-octadecenoic acid was formed only when germinated barley was the enzyme source.Lipoxygenase was readily extracted by buffer, but hydroperoxide isomerase was bound in a catalytically active state to the insoluble barley grist and was efficientiy extracted only when Triton X-100 was included in the extraction buffer. Hydroperoxide isomerase was locallzed in the embryo of quiescent barley, but it was present in the embryo, acrospire, and in small but concentrated amounts in the rootiet of germinating barley. The levels of both Lipoxygenase and hydroperoxide isomerase increased through the thirteenth day of germination.The importance of the LOX4 system to lipid metabolism in plant biochemistry and physiology is indicated by its near ubiquitous distribution in the plant kingdom (2)

Specific Adduction of Plant Lipid Transfer Protein by an Allene Oxide Generated by 9-Lipoxygenase and Allene Oxide Synthase

“…an ␣-ketol, and (ii) by reproducing adduction by exposing LTP1 to either linoleic acid and an aqueous suspension of isolated defatted barley embryo or 9-HPOD and maize AOS. 9-LOX and AOS are specifically located in the embryo (40,41), in agreement with the fact that LTP1 adduction requires the presence of the embryo.…”

“…It should be noted that 9-LOX is the major LOX in the embryo of quiescent barley seeds (42,43) and that AOS is the major enzyme metabolizing lipoxygenase-generated hydroperoxides in embryos of quiescent barley grains (41). The very efficient trapping of 9,10-allene oxide by 50 M LTP1 in an aqueous environment (about 55 M water) (Fig.…”

Lipoxygenase in Sweet Corn Germ: Isolation and Physicochemical Properties

“…Gardner (1970) reported that lipoxygenase was localized primarily in the seed germ tissue of mature hybrid corn. Lipoxygenase activity was found primarily in the germ tissue of cereal seeds such as wheat (Auerman et al, 1971;Von Ceumern and Hartfiel, 1984), barley (Lulai and Baker, 1976;Lulai et al, 1981), and rice (Yamamoto et al, 1980); however, the subcellular location of lipoxygenase in germ tissue has not been reported (Gardner, 1988).…”

Characterization of Factors Involved in the Production of 2(E)-Nonenal during Mashing

“…We think that this inconsistency is due to the presence of other competing pathways to the transformation of 2( E )-nonenal. Competing enzymes for 9-HPL-like activity would be hydroperoxide isomerase, 12,13) peroxygenase-like activity, 8,15) or allene oxide synthase. 19) In soybean seeds, it is reported that HPL cleaves 9-HPOD to form 3(Z )-nonenal, and then 3(Z )-nonenal is sequentially converted into 4-hydroperoxy-2( E )-nonenal and 4-hydroxy-2( E )-nonenal by the action of soybean LOX-1 and peroxygenase, respectively.…”

“…It was only characterized as an enzyme that converts 13-HPOD into a-ketol [9-hydroxy-10-oxo-(12Z )-octadecenoic acid] and gketol [13-hydroxy 10-oxo-(11 E )-octadecenoic acid], so that the possibility that it might also contain HPL has not been veriˆed. 12,13) Schwarz and Pyler reported that hydroperoxide-decomposing activity is also detected in malt, but only if it is extracted with a buŠer containing Triton X-100, suggesting the enzyme is tightly bound to the insoluble barley grist. 14) Because this activity was not detectable in the soluble fraction of mash at any time during mashing, they concluded this activity is not involved in the lipid oxidation.…”