Oxylipin Biosynthesis Research Articles

Oxylipins: Structurally diverse metabolites from fatty acid oxidation

Oxylipins are lipophilic signaling molecules derived from the oxidation of polyunsaturated fatty acids. Initial fatty acid oxidation occurs mainly by the enzymatic or chemical formation of fatty acid hydroperoxides. An array of alternative reactions further converting fatty acid hydroperoxides gives rise to a multitude of oxylipin classes, many with reported signaling functions in plants. Oxylipins include the phytohormone, jasmonic acid, and a number of other molecules including hydroxy-, oxo- or keto-fatty acids or volatile aldehydes that may perform various biological roles as second messengers, messengers in inter-organismic signaling, or even as bactericidal agents. The structural diversity of oxylipins is further increased by esterification of the compounds in plastidial glycolipids, for instance the Arabidopsides, or by conjugation of oxylipins to amino acids or other metabolites. The enzymes involved in oxylipin metabolism are diverse and comprise a multitude of examples with interesting and unusual catalytic properties. In addition, the interplay of different subcellular compartments during oxylipin biosynthesis suggests complex mechanisms of regulation that are not well understood. This review aims at giving an overview of plant oxylipins and the multitude of enzymes responsible for their biosynthesis.

Acaricidal effects of natural six-carbon and nine-carbon aldehydes on stored-product mites

The toxicities of three plant volatiles, (2E)-hexenal, (2E, 6Z)-nonadienal and (2E)-nonenal, intermediate products of the oxylipin biosynthesis pathway, were tested on three mites of importance for medical purposes and as pests. The aldehydes were diluted in hexane separately and incorporated into diets in ranges of 4-143 mg g(-1). The final density of mites in control and aldehyde-enriched diets was compared after 21 days. The aldehydes were toxic to the mites, whose final density showed an inverse correlation with aldehyde concentration. In addition to the effects of aldehyde concentration, the final density of mites was also influenced by the different aldehydes tested and the interaction among aldehyde concentration and chemical structure. In a functional combination of aldehydes and species, the doses calculated for growth inhibition and eradication of mites ranged from 4 to 35 mg g(-1) and from 36 to 314 mg g(-1), respectively. Due to the protective role displayed by natural six-carbon and nine-carbon aldehydes, these compounds are potential candidates for controlling stored-product mites in stored food and feed products.

Identification of Dioxygenases Required for Aspergillus Development

Aspergillus sp. contain ppoA, ppoB, and ppoC genes, which code for fatty acid oxygenases with homology to fungal linoleate 7,8-diol synthases (7,8-LDS) and cyclooxygenases. Our objective was to identify these enzymes, as ppo gene replacements show critical developmental aberrancies in sporulation and pathogenicity in the human pathogen Aspergillus fumigatus and the genetic model Aspergillus nidulans. The PpoAs of A. fumigatus and A. nidulans were identified as (8R)-dioxygenases with hydroperoxide isomerase activity, designated 5,8-LDS. 5,8-LDS transformed 18:2n-6 to (8R)-hydroperoxyoctadecadienoic acid ((8R)-HPODE) and (5S,8R)-dihydroxy-9Z,12Z-octadecadienoic acid ((5S,8R)-DiHODE). We also detected 8,11-LDS in A. fumigatus and (10R)-dioxygenases in both Aspergilli. The diol synthases oxidized [(8R)-(2)H]18:2n-6 to (8R)-HPODE with retention of the deuterium label, suggesting antarafacial hydrogen abstraction and insertion of molecular oxygen. Experiments with stereospecifically deuterated 18:2n-6 showed that (8R)-HPODE was isomerized by 5,8- and 8,11-LDS to (5S,8R)-DiHODE and to (8R,11S)-dihydroxy-9Z,12Z-octadecadienoic acid, respectively, by suprafacial hydrogen abstraction and oxygen insertion at C-5 and C-11. PpoCs were identified as (10R)-dioxygenases, which catalyzed abstraction of the pro-S hydrogen at C-8 of 18:2n-6, double bond migration, and antafacial insertion of molecular oxygen with formation of (10R)-hydroxy-8E,12Z-hydroperoxyoctadecadienoic acid ((10R)-HPODE). Deletion of ppoA led to prominent reduction of (8R)-H(P)ODE and complete loss of (5S,8R)-DiHODE biosynthesis, whereas biosynthesis of (10R)-HPODE was unaffected. Deletion of ppoC caused biosynthesis of traces of racemic 10-HODE but did not affect the biosynthesis of other oxylipins. We conclude that ppoA of Aspergillus sp. may code for 5,8-LDS with catalytic similarities to 7,8-LDS and ppoC for linoleate (10R)-dioxygenases. Identification of these oxygenases and their products will provide tools for analyzing the biological impact of oxylipin biosynthesis in Aspergilli.

Wounding and pathogen infection induce a chloroplast-targeted lipoxygenase in the common bean (Phaseolus vulgaris L.)

Chloroplastic LOXs are implicated in the biosynthesis of oxylipins like jasmonic acid and C6 volatiles among others. In this study, we isolated the cDNA of a novel chloroplast-targeted Phaseolus vulgaris LOX, (PvLOX6). This gene is highly induced after wounding, non-host pathogen infection, and by signaling molecules as H2O2, SA, ethylene and MeJA. The phylogenetic analysis of PvLOX6 showed that it is closely related to chloroplast-targeted LOX from potato (H1) and tomato (TomLOXC); both of them are implicated in the biosynthesis of C6 volatiles. Induction of PvLOX6 mRNA by wounding ethylene and jasmonic acid on the one side, and non-host pathogen, salicylic acid on the other indicates that common bean uses the same LOX to synthesize oxylipins in response to different stresses.

AtPLAI Is an Acyl Hydrolase Involved in Basal Jasmonic Acid Production and Arabidopsis Resistance to Botrytis cinerea

Intracellular phospholipase A2 (PLA2) plays an important role in regulating oxylipin biosynthesis in mammals, but the molecular and biochemical nature of intracellular PLA2 is not well understood in plants. Arabidopsis thaliana gene At1g61850 (AtPLAI) encodes a 140-kDa protein that is most similar to mammalian calcium-independent PLA2, and additionally contains leucine-rich repeats and Armadillo repeats. AtPLAI hydrolyzes phospholipids at both the sn-1 and sn-2 positions, but prefers galactolipids to phospholipids as substrates. Profiling of lipid species altered in response to the necrotrophic fungus Botrytis cinerea revealed decreases in the levels of phosphatidylglycerol and digalactosyldiacylglycerol, suggesting that hydrolysis of plastidic polar lipids might provide precursors for pathogen-induced jasmonic acid (JA) production. Disruption of AtPLAI by T-DNA insertion reduced the basal level of JA, but did not impede pathogen-induced production of JA, free linolenic acid, or hydrolysis of plastidic lipids. Still, AtPLAI-deficient plants exhibited more damage than wild type plants after B. cinerea infection, and pretreatment of plants with methyl jasmonate alleviated pathogen damage to the mutant plants. The study shows that AtPLAI is an acyl hydrolase, rather than a specific phospholipase A. AtPLAI is involved in basal JA production and Arabidopsis resistance to the necrotrophic fungus B. cinerea.

Wounding stimulates the accumulation of glycerolipids containing oxophytodienoic acid and dinor-oxophytodienoic acid in Arabidopsis leaves.

Although oxylipins can be synthesized from free fatty acids, recent evidence suggests that oxylipins are components of plastid-localized polar complex lipids in Arabidopsis (Arabidopsis thaliana). Using a combination of electrospray ionization (ESI) collisionally induced dissociation time-of-flight mass spectrometry (MS) to identify acyl chains, ESI triple-quadrupole (Q) MS in the precursor mode to identify the nominal masses of complex polar lipids containing each acyl chain, and ESI Q-time-of-flight MS to confirm the identifications of the complex polar lipid species, 17 species of oxylipin-containing phosphatidylglycerols, monogalactosyldiacylglycerols (MGDG), and digalactosyldiacylglycerols (DGDG) were identified. The oxylipins of these polar complex lipid species include oxophytodienoic acid (OPDA), dinor-OPDA (dnOPDA), 18-carbon ketol acids, and 16-carbon ketol acids. Using ESI triple-Q MS in the precursor mode, the accumulation of five OPDA- and/or dnOPDA-containing MGDG and two OPDA-containing DGDG species were monitored as a function of time in mechanically wounded leaves. In unwounded leaves, the levels of these oxylipin-containing complex lipid species were low, between 0.001 and 0.023 nmol/mg dry weight. However, within the first 15 min after wounding, the levels of OPDA-dnOPDA MGDG, OPDA-OPDA MGDG, and OPDA-OPDA DGDG, each containing two oxylipin chains, increased 200- to 1,000-fold. In contrast, levels of OPDA-hexadecatrienoic acid MGDG, linolenic acid (18:3)-dnOPDA MGDG, OPDA-18:3 MGDG, and OPDA-18:3 DGDG, each containing a single oxylipin chain, rose 2- to 9-fold. The rapid accumulation of high levels of galactolipid species containing OPDA-OPDA and OPDA-dnOPDA in wounded leaves is consistent with these lipids being the primary products of plastidic oxylipin biosynthesis.

Evaluation of the Antimicrobial Activities of Plant Oxylipins Supports Their Involvement in Defense against Pathogens

Plant oxylipins are a large family of metabolites derived from polyunsaturated fatty acids. The characterization of mutants or transgenic plants affected in the biosynthesis or perception of oxylipins has recently emphasized the role of the so-called oxylipin pathway in plant defense against pests and pathogens. In this context, presumed functions of oxylipins include direct antimicrobial effect, stimulation of plant defense gene expression, and regulation of plant cell death. However, the precise contribution of individual oxylipins to plant defense remains essentially unknown. To get a better insight into the biological activities of oxylipins, in vitro growth inhibition assays were used to investigate the direct antimicrobial activities of 43 natural oxylipins against a set of 13 plant pathogenic microorganisms including bacteria, oomycetes, and fungi. This study showed unequivocally that most oxylipins are able to impair growth of some plant microbial pathogens, with only two out of 43 oxylipins being completely inactive against all the tested organisms, and 26 oxylipins showing inhibitory activity toward at least three different microbes. Six oxylipins strongly inhibited mycelial growth and spore germination of eukaryotic microbes, including compounds that had not previously been ascribed an antimicrobial activity, such as 13-keto-9(Z),11(E),15(Z)-octadecatrienoic acid and 12-oxo-10,15(Z)-phytodienoic acid. Interestingly, this first large-scale comparative assessment of the antimicrobial effects of oxylipins reveals that regulators of plant defense responses are also the most active oxylipins against eukaryotic microorganisms, suggesting that such oxylipins might contribute to plant defense through their effects both on the plant and on pathogens, possibly through related mechanisms.

Comparison of Fatty Acid Composition of Cell Homogenates and Isolated Chloroplasts in Acetabularia crenulata (Lamouroux)

Algal preparations from Acetabularia crenulata were analyzed for their fatty acid composition to establish the suitability of this alga as a model to study fatty acid oxidation and oxylipin biosynthesis. The work was based on two goals. The first goal of this study was to determine the contribution of fatty acids from contaminating bacteria and how this influenced the total fatty acid composition of cell homogenates of A. crenulata collected in the wild as compared to specimens cultured in sterile conditions. The major fatty acids detected for both specimens were palmitic (C16:0), palmitoleic (C16:1n-7), oleic (C18:1n-9), linoleic (C18:2n-6), linolenic (C18:3n-3), and octadecatetraenoic acid (C18:4n-3). Significant amounts of odd-chain fatty acids common to bacteria were not detected in either sample. Furthermore, branched-chain fatty acids, typical bacterial biomarkers, were not detected in either sample. Data suggest that bacteria do not greatly contribute to the total fatty acid pool of A. crenulata. The second goal was to compare the fatty acid composition of cell homogenates with that of isolated chloroplasts. Comparatively speaking palmitoleic and octadecatetraenoic acid were found at significantly lower concentrations in the chloroplast whereas oleic and linolenic acid were found at significantly higher amounts in this organelle. Furthermore, the amount of hexadecatrienoic acid (C16:3), a fatty acid commonly esterified to monogalactosyldiacylglycerol (MGDG; lipid present at high concentrations inside the chloroplasts of algae), was present at very low concentrations in these plastids (0.7%). Typically green algal follow the "prokaryotic pathway" for MGDG biosynthesis where C18:3 is esterified at the sn-1 position of the glycerol backbone and C18:3 or C16:3 at the sn-2 position, making C16:3 a major fatty acid inside chloroplasts. Interestingly, our results suggest that chloroplasts of A. crenulata appear to follow the "eukaryotic pathway" for MGDG biosynthesis where C18:3 is both at the sn-1 and sn-2 position of MGDG. Taking into account the exceptions noted, the fatty acid composition for A. crenulata is similar to that reported for most chlorophytes.

A Multifunctional Lipoxygenase with Fatty Acid Hydroperoxide Cleaving Activity from the Moss Physcomitrella patens

A complex mixture of fatty acid-derived aldehydes, ketones, and alcohols is released upon wounding of the moss Physcomitrella patens. To investigate the formation of these oxylipins at the molecular level we isolated a lipoxygenase from P. patens, which was identified in an EST library by sequence homology to lipoxygenases from plants. Sequence analysis of the cDNA showed that it exhibits a domain structure similar to that of type2 lipoxygenases from plants, harboring an N-terminal import signal for chloroplasts. The recombinant protein was identified as arachidonate 12-lipoxygenase and linoleate 13-lipoxygenase with a preference for arachidonic acid and eicosapentaenoic acid. In contrast to any other lipoxygenase cloned so far, this enzyme exhibited in addition an unusual high hydroperoxidase and also a fatty acid chain-cleaving lyase activity. Because of these unique features the pronounced formation of (2Z)-octen-1-ol, 1-octen-3-ol, the dienal (5Z,8Z,10E)-12-oxo-dodecatrienoic acid and 12-keto eicosatetraenoic acid was observed when arachidonic acid was administered as substrate. 12-Hydroperoxy eicosatetraenoic acid was found to be only a minor product. Moreover, the P. patens LOX has a relaxed substrate tolerance accepting C(18)-C(22) fatty acids giving rise to even more LOX-derived products. In contrast to other lipoxygenases a highly diverse product spectrum is formed by a single enzyme accounting for most of the observed oxylipins produced by the moss. This single enzyme might, in a fast and effective way, be involved in the formation of signal and/or defense molecules thus contributing to the broad resistance of mosses against pathogens.

Convergent responses to stress. Solar ultraviolet-B radiation and Manduca sexta herbivory elicit overlapping transcriptional responses in field-grown plants of Nicotiana longiflora.

The effects of solar ultraviolet (UV)-B (280-315 nm) on plants have been studied intensively over the last 2 decades in connection with research on the biological impacts of stratospheric ozone depletion. However, the molecular mechanisms that mediate plant responses to solar (ambient) UV-B and their interactions with response mechanisms activated by other stressors remain for the most part unclear. Using a microarray enriched in wound- and insect-responsive sequences, we examined expression responses of 241 genes to ambient UV-B in field-grown plants of Nicotiana longiflora Cav. Approximately 20% of the sequences represented on the array showed differential expression in response to solar UV-B. The expression responses to UV-B had parallels with those elicited by simulated Manduca sexta herbivory. The most obvious similarities were: (a) down-regulation of several photosynthesis-related genes, and (b) up-regulation of genes involved in fatty acid metabolism and oxylipin biosynthesis such as HPL (hydroperoxide lyase), alpha-DIOX (alpha-dioxygenase), LOX (13-lipoxygenase), and AOS (allene oxide synthase). Genes encoding a WRKY transcription factor, a ferredoxin-dependent glutamate-synthase, and several other insect-responsive genes of unknown function were also similarly regulated by UV-B and insect herbivory treatments. Our results suggest that UV-B and caterpillar herbivory activate common regulatory elements and provide a platform for understanding the mechanisms of UV-B impacts on insect herbivory that have been documented in recent field studies.

Cyclopentenone isoprostanes induced by reactive oxygen species trigger defense gene activation and phytoalexin accumulation in plants.

Lipid peroxidation may be initiated either by lipoxygenases or by reactive oxygen species (ROS). Enzymatic oxidation of alpha-linolenate can result in the biosynthesis of cyclic oxylipins of the jasmonate type while free-radical-catalyzed oxidation of alpha-linolenate may yield several classes of cyclic oxylipins termed phytoprostanes in vivo. Previously, we have shown that one of these classes, the E1-phytoprostanes (PPE1), occurs ubiquitously in plants. In this work, it is shown that PPE1 are converted to novel cyclopentenone A1- and B1-phytoprostanes (PPA1 and PPB1) in planta. Enhanced formation of PPE1, PPA1, and PPB1 is observed after peroxide stress in tobacco cell cultures as well as after infection of tomato plants with a necrotrophic fungus, Botrytis cinerea. PPA1 and PPB1 display powerful biologic activities including activation of mitogen-activated protein kinase (MAPK) and induction of glutathione-S-transferase (GST), defense genes, and phytoalexins. Data collected so far infer that enhanced phytoprostane formation is a general consequence of oxidative stress in plants. We propose that phytoprostanes are components of an oxidant-injury-sensing, archaic signaling system that serves to induce several plant defense mechanisms.

Identification of a Jasmonate-regulated Allene Oxide Synthase That Metabolizes 9-Hydroperoxides of Linoleic and Linolenic Acids

Allene oxide synthase (AOS) is a cytochrome P-450 (CYP74A) that catalyzes the first step in the conversion of 13-hydroperoxy linolenic acid to jasmonic acid and related signaling molecules in plants. Here, we report the molecular cloning and characterization of a novel AOS-encoding cDNA (LeAOS3) from Lycopersicon esculentum whose predicted amino acid sequence classifies it as a member of the CYP74C subfamily of enzymes that was hitherto not known to include AOSs. Recombinant LeAOS3 expressed in Escherichia coli showed spectral characteristics of a P-450. The enzyme transformed 9- and 13-hydroperoxides of linoleic and linolenic acid to alpha-ketol, gamma-ketol, and cyclopentenone compounds that arise from spontaneous hydrolysis of unstable allene oxides, indicating that the enzyme is an AOS. Kinetic assays demonstrated that LeAOS3 was approximately 10-fold more active against 9-hydroperoxides than the corresponding 13-isomers. LeAOS3 transcripts accumulated in roots, but were undetectable in aerial parts of mature plants. In contrast to wild-type plants, LeAOS3 expression was undetectable in roots of a tomato mutant that is defective in jasmonic acid signaling. These findings suggest that LeAOS3 plays a role in the metabolism of 9-lipoxygenase-derived hydroperoxides in roots, and that this branch of oxylipin biosynthesis is regulated by the jasmonate signaling cascade.

The biosynthesis of oxylipins of linoleic and arachidonic acids by the sewage fungus Leptomitus lacteus, including the identification of 8R-Hydroxy-9Z,12Z-octadecadienoic acid.

When the sewage fungus Leptomitus lacteus was grown in liquid culture aerobically and then transferred to medium containing long-chain fatty acids, it produced a number of oxygenated fatty acids. From linoleic acid (18:2n-6), the major metabolite produced was R-8-hydroxy-9Z,12Z-octadecadienoic acid (8R-HODE), with additional quantities of 8,11-di-HODE, 11,16-di-HODE, and 11,17-di-HODE. Other fatty acid derivatives identified included 7-HODE, 10-HODE, and 13-hydroxy-octadecamonoenoic acid. Arachidonic acid (20:4n-6) was metabolized primarily to 18- and 19-hydroxy-eicosatetraenoic acids (18- and 19-HETE) also as R enantiomers, along with smaller quantities of 17-HETE, 9-HETE, 14,15-dihydroxy-eicosatrienoic acid and 11,12,19-trihydroxy-eicosatrienoic acid. The oxygenated products of long-chain fatty acids, in particular the biosynthesis of 8R-HODE, a compound classified as a precocious sporulation inducer, were similar to those produced by an unrelated fungal species in the Ascomycota, the take-all fungus Gaeumannomyces graminis. As in G. graminis, the biotransformation of linoleate to 8R-HODE was not significantly inhibited by exposure of the organism to CO. This indicated that the enzyme responsible for 8R-HODE biosynthesis in Leptomitus could be similar to that of G. graminis; yet we did not detect 7,8-di-HODE as a product of 18:2n-6 metabolism as in G. graminis. CO did inhibit the biosynthesis of 14,15-di-HETE, 18-HETE, and 19-HETE in L. lacteus, which suggested the involvement of a cytochrome P450-type monooxygenase. The biosynthesis of 8R-HODE from 18:2n-6 was found to occur in certain cell lysates, specifically in low speed (15,000 x g) supernatant, following cell disruption.

An epoxy alcohol synthase pathway in higher plants: biosynthesis of antifungal trihydroxy oxylipins in leaves of potato.

[1-14C]Linoleic acid was incubated with a whole homogenate preparation of potato leaves (Solanum tuberosum L., var. Bintje). The methyl-esterified product was subjected to straight-phase high-performance liquid chromatography and was found to contain four major radioactive oxidation products, i.e., the epoxy alcohols methyl 10(S),11(S)-epoxy-9(S)-hydroxy-12(Z)-octadecenoate (14% of the recovered radioactivity) and methyl 12(R), 13(S)-epoxy-9(S)-hydroxy-10(E)-octadecenoate (14%), and the trihydroxy derivatives methyl 9(S),10(S),11(R)-trihydroxy-12(Z)-octadecenoate (18%)and methyl 9(S), 12(S),13(S)-trihydroxy-10(E)-octadecenoate (30%). The structures and stereochemical configurations of these oxylipins were determined by chemical and spectral methods using the authentic compounds as references. Incubations performed in the presence of glutathione peroxidase revealed that lipoxygenase activity of potato leaves generated the 9- and 13-hydroperoxides of linoleic acid in a ratio of 95:5. Separate incubations of these hydroperoxides showed that linoleic acid 9(S)-hydroperoxide was metabolized into epoxy alcohols by particle-bound epoxy alcohol synthase activity, whereas the 13-hydroperoxide was metabolized into alpha- and gamma-ketols by a particle-bound allene oxide synthase. It was concluded that the main pathway of linoleic acid metabolism in potato leaves involved 9-lipoxygenase-catalyzed oxygenation into linoleic acid 9(S)-hydroperoxide followed by rapid conversion of this hydroperoxide into epoxy alcohols and a slower, epoxide hydrolase-catalyzed conversion of the epoxy alcohols into trihydroxy-octadecenoates. Trihydroxy derivatives of linoleic and linolenic acids have previously been reported to be growth-inhibitory to plant-pathogenic fungi, and a role of the new pathway of linoleic acid oxidation in defense reactions against pathogens is conceivable.

Biological activity and biosynthesis of pentacyclic oxylipins: The linoleic acid pathway

The relevance of the postulated pathway from linoleic acid to dihydrojasmonic acid is analysed. Pentacyclic oxylipins having pentenyl or pentyl side chains were tested for their secondary metabolite inducing activity in seven different plant cell culture species which all responded well to 12-oxo-phytodienoic acid and jasmonic acid. The response towards the dihydro-derivatives 15,16-dihydro-12-oxo-phytodienoic acid and 9,10-dihydrojasmonic acid ranged from strong activity in Eschscholzia californica to no activity in Lycopersicon esculentum. 15,16-Dihydro-12-oxo-phytodienoic acid can be formed from linoleic acid (18:2) by a linseed acetone powder enzyme preparation. Application experiments with linoleic (18:2) and linolenic acid (18:3) showed that the bottleneck of the 18:2 pathway is most likely the cyclization of the intermediate allene oxide when compared to the ease by which 15,16-dihydro-12-oxo-phytodienoic acid is converted to dihydrojasmonic acid in plant systems. The metabolism of potential precursors of jasmonic and dihydrojasmonic acid was extensively studied in various cell cultures.

On the mechanism of biosynthesis of divinyl ether oxylipins by enzyme from garlic bulbs.

The microsomal fraction of homogenate of garlic (Allium sativum L.) bulbs contains a divinyl ether synthase which catalyzes conversion of (9Z,11E,13S)-13-hydroperoxy-9, 11-octadecadienoic acid and (9Z,11E,13S,15Z)-13-hydroperoxy-9,11,15-octadecatri eno ic acid into (9Z,11E,1'E,)-12-(1'-hexenyloxy)-9,11-dodecadienoic acid (etherolenic acid) and (9Z,11E,1'E,3'Z)-12-(1',3'-hexadienyloxy)-9,11-dode cadienoic acid (etherolenic acid), respectively. Two isomers of etherolenic acid were isolated. As shown by NMR spectrometry, the double bond configurations of these compounds were (9E,11E,1'E) and (9Z,11Z,1'E). Experiments with linoleic acid (13R,S)-hydroperoxide demonstrated that the S enantiomer was a much better substrate for the divinyl ether synthase compared to the R enantiomer. Incubation of (9Z,11E,13S)-[18O2]hydroperoxy-9,11-octadecadienoic acid led to the formation of etherolenic acid which retained 18O in the ether oxygen. An intermediary role of an epoxyallylic cation in etherolenic acid biosynthesis is postulated.

Catalytic and spectroscopic properties of linoleate diol synthase of the fungus Gaümannomyces graminis.

The fungus Gaümannomyces graminis causes “take-all”, a devastating root disease of wheat. Our interest in G. graminis is due to its biosynthesis of oxylipins, which might be important for sporulation. The fungus can sequentially metabolize linoleic acid (18: 2n-6) to 8R-hydroperoxylinoleic acid (8-HPODE) through an 8-dioxvgenase and to 7S,8S-dihydroxylinoleic acid (7,8-DiHODE) through a hydroperoxide isomerase1–3. A highly purified protein with both enzyme activities was recently found to be a hemoprotein4. The protein had an apparent molecular size of 130 kDa on SDA-PAGE and it appeared to be a tetramer on gel filtration. The protein will be referred to as linoleate diol synthase.KeywordsLinoleic AcidHigh Spin StateHydrogen AbstractionDiethyl PyrocarbonateProton AbstractionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Biosynthesis of novel divinyl ether oxylipins by enzyme from garlic (Allium sativum L.) bulbs.

First fatty acid divinyl ethers colneleic and colnelenic acids were detected by Galliard et al.1, 2 in in vitro experiments with potato tubers. Formation of these oxylipins, is controlled by 9-lipoxygenase activity and an enzyme, controlling dehydration of 9-hydroperoxide. Such a pathway, being not found in any other plant or animal species, was considered to be the unique property of potato tubers. Our recent in vitro studies of lipoxygenase pathway in garlic bulbs led to detection of novel divinyl ethers 12-[1′(E)-hexenyloxy]-9(Z),11(E)-dodecadienoic (etheroleic) and 12-[1′(E),3′(Z)-hexadienyloxy]-9(Z),11(E)-dodecadienoic (etherolenic) acids3, products of 13-hydroperoxides of linoleic and linolenic acids (13-HPOD and 13-HPOT) conversion, respectively.