Production Of Unsaturated Fatty Acids Research Articles

Variation of Δ9-Desaturase Activity in Dairy Cattle

The endogenous production of unsaturated fatty acids (FA), particularly some monounsaturated FA (%MONO) and nearly all conjugated linoleic acids, is regulated by the Δ9-desaturase activity. The aims of this study were to assess the variation of this enzymatic activity within lactation, across dairy breeds, and to estimate its genetic parameters. The ratios of C14:1 cis-9 to C14:0, C16:1 cis-9 to C16:0, and C18:1 cis to C18:0 were calculated from FA contents predicted by mid-infrared spectrometry. Variance components and standard errors were estimated using average information REML. The multitrait mixed model included as fixed effects herd × test date × class of lactation number, class of days in milk × class of lactation number, class of age × class of lactation number, and regressions on breed composition. Four random effects were also included: animal genetic effect, 2 permanent environments (within and across lactations), and residual effect. Under the assumption that the calculated ratios are an approximate measurement of Δ9-desaturase activity, this study showed different sources of variation for this enzymatic activity. A slight difference was observed within lactation. The ratios of C14:1 cis-9 to C14:0 and C16:1 cis-9 to C16:0 increased as a function of days in milk. Differences across 7 dairy breeds were observed. The values of Δ9-desaturase indices observed for Jersey and Brown-Swiss cows were lower compared with Holstein. The opposite was observed for dual-purpose Belgian Blue cows. Values of heritability for the ratios of C14:1 cis-9 to C14:0, C16:1 cis-9 to C16:0, and C18:1 cis to C18:0 were 20, 20, and 3%, respectively. Negative genetic correlations observed between fat or protein contents and the 3 indices suggested that an increased activity of Δ9-desaturase could inhibit the synthesis of fat and protein in bovine milk. Negative correlations were also observed between fat or protein contents and the contents of 3 studied unsaturated FA in milk fat (C14:1 cis-9, C16:1 cis-9, and C18:1 cis). The positive genetic correlations observed between %MONO and the ratios of C14:1 cis-9 to C14:0 (0.72), C16:1 cis-9 to C16:0 (0.62), and C18:1 cis to C18:0 (0.97) showed that %MONO is linked to the Δ9-desaturase activity.

Nitroalkenes Suppress Lipopolysaccharide-Induced Signal Transducer and Activator of Transcription Signaling in Macrophages: A Critical Role of Mitogen-Activated Protein Kinase Phosphatase 1

Nitration products of unsaturated fatty acids are formed via NO-dependent oxidative reactions and appear to be a new class of endogenous antiinflammatory mediators. Nitroalkene derivatives of nitrated linoleic acid (LNO(2)) and nitrated oleic acid (OA-NO(2)) alleviate inflammatory responses in macrophages, but the underlying mechanisms remain to be fully defined. Herein we report that LNO(2) and OA-NO(2) suppress proinflammatory signal transducer and activator of transcription (STAT) signaling in macrophages. In RAW264.7 cells, a murine macrophage cell line, LNO(2) and OA-NO(2) inhibited the lipopolysaccharide (LPS)-induced STAT1 phosphorylation and the STAT1-dependent transcriptional activity, thereby suppressing expression of its target gene such as iNOS and MCP-1. The nitroalkene-mediated inhibition of STAT1 activity was not affected by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (a NO scavenger), GW9662 (a peroxisome proliferator-activated receptor-gamma-specific antagonist) or glutathione (an antioxidant), suggesting an underlying mechanism independent of NO, peroxisome proliferator-activated receptor-gamma, or thio-nitralkylation. In contrast, LNO(2) or OA-NO(2) alone up-regulated both mRNA and protein levels of MAPK phosphatase 1 (MKP-1) and strongly augmented the LPS-induced MKP-1 protein expression. Knockdown of MKP-1 by MKP-1 small interfering RNA enhanced the LPS-induced STAT1 phosphorylation, suggesting that MKP-1 acts as a negative regulator for LPS-induced STAT signaling. In addition, the nitroalkene-mediated inhibitory effects on STAT1 phosphorylation, iNOS expression, and MCP-1 secretion were also largely attenuated by the MKP-1 small interfering RNA approach. Taken together, our data demonstrate that nitroalkenes inhibit proinflammatory STAT signaling through inducting MKP-1 in macrophages.

Role of MGA2 in regulation of lipid metabolism in Saccharomyces cerevisiae

The Saccharomyces cerevisiae MGA2 gene encodes a protein that is an important regulator of lipid metabolism in the cell. Mga2p plays a major role in unsaturated fatty acid production through its regulation of the transcription and mRNA stability of OLE1, whose product is the Δ‐9 fatty acid desaturase. We have found that mga2Δ strains also contain elevated relative amounts of squalene, a sterol pathway intermediate, when compared to wild‐type cells. A possible explanation for the higher squalene levels detected in mga2Δ cells is lower expression of the ERG1 gene. ERG1 encodes squalene epoxidase, which catalyzes the conversion of squalene to squalene epoxide. To explore whether MGA2 plays a role in regulating ERG1 expression, we first examined effects on ERG1 transcription using a promoter‐lacZ reporter gene. We report here that in addition to MGA2's role in regulation of unsaturated fatty acids, MGA2 is required for full basal expression of ERG1. In contrast to OLE1, we found that ERG1 expression was not repressed by unsaturated fatty acids. However, ERG1 expression was elevated in response to miconazole, an inhibitor of sterol synthesis in yeast

Characterization of organosulfates from the photooxidation of isoprene and unsaturated fatty acids in ambient aerosol using liquid chromatography/(−) electrospray ionization mass spectrometry

In the present study, we have characterized in detail the MS(2) and MS(3) fragmentation behaviors, using electrospray ionization (ESI) in the negative ion mode, of previously identified sulfated isoprene secondary organic aerosol compounds, including 2-methyltetrols, 2-methylglyceric acid, 2-methyltetrol mononitrate derivatives, glyoxal and methylglyoxal. A major fragmentation pathway for the deprotonated molecules of the sulfate esters of 2-methyltetrols and 2-methylglyceric acid and of the sulfate derivatives of glyoxal and methylglyoxal is the formation of the bisulfate [HSO(4)](-) anion, while the deprotonated sulfate esters of 2-methyltetrol mononitrate derivatives preferentially fragment through loss of nitric acid. Rational interpretation of MS(2), MS(3) and accurate mass data led to the structural characterization of unknown polar compounds in K-puszta fine aerosol as organosulfate derivatives of photooxidation products of unsaturated fatty acids, i.e. 2-hydroxy-1,4-butanedialdehyde, 4,5- and 2,3-dihydroxypentanoic acids, and 2-hydroxyglutaric acid, and of alpha-pinene, i.e. 3-hydroxyglutaric acid. The deprotonated molecules of the sulfated hydroxyacids, 2-methylglyceric acid, 4,5- and 2,3-dihydroxypentanoic acid, and 2- and 3-hydroxyglutaric acids, showed in addition to the [HSO(4)](-) ion (m/z 97) neutral losses of water, CO(2) and/or SO(3), features that are characteristic of humic-like substances. The polar organosulfates characterized in the present work are of climatic relevance because they may contribute to the hydrophilic properties of fine ambient aerosol. In addition, these compounds probably serve as ambient tracer compounds for the occurrence of secondary organic aerosol formation under acidic conditions.

Fatty Acid Desaturation and the Regulation of Adiposity in Caenorhabditis elegans

Monounsaturated fatty acids are essential components of membrane and storage lipids. Their synthesis depends on the conversion of saturated fatty acids to unsaturated fatty acids by Delta9 desaturases. Caenorhabditis elegans has three Delta9 desaturases encoded by the genes fat-5, fat-6, and fat-7. We generated nematodes that display a range of altered fatty acid compositions by constructing double-mutant strains that combine mutations in fat-5, fat-6, and fat-7. All three double-mutant combinations have reduced survival at low temperatures. The fat-5;fat-6 double mutants display relatively subtle fatty acid composition alterations under standard conditions, but extreme fatty acid composition changes and reduced survival in the absence of food. The strain with the most severe defect in the production of unsaturated fatty acids, fat-6;fat-7, exhibits slow growth and reduced fertility. Strikingly, the fat-6;fat-7 double-mutant animals have decreased fat stores and increased expression of genes involved in fatty acid oxidation. We conclude that the Delta9 desaturases, in addition to synthesizing unsaturated fatty acids for properly functioning membranes, play key roles in lipid partitioning and in the regulation of fat storage.

Nitro-linoleic acid inhibits vascular smooth muscle cell proliferation via the Keap1/Nrf2 signaling pathway

Nitroalkenes, the nitration products of unsaturated fatty acids formed via NO-dependent oxidative reactions, have been demonstrated to exert strong biological actions in endothelial cells and monocytes/macrophages; however, little is known about their effects on vascular smooth muscle cells (VSMCs). The present study examined the role of nitro-linoleic acid (LNO(2)) in the regulation of VSMC proliferation. We observed that LNO(2) inhibited VSMC proliferation in a dose-dependent manner. In addition, LNO(2) induced growth arrest of VSMCs in the G(1)/S phase of the cell cycle with an upregulation of the cyclin-dependent kinase inhibitor p27(kip1). Furthermore, LNO(2) triggered nuclear factor-erythroid 2-related factor 2 (Nrf2) nuclear translocation and activation of the antioxidant-responsive element-driven transcriptional activity via impairing Kelch-like ECH-associating protein 1 (Keap1)-mediated negative control of Nrf2 activity in VSMCs. LNO(2) upregulated the expression of Nrf2 protein levels, but not mRNA levels, in VSMCs. A forced activation of Nrf2 led to an upregulation of p27(kip1) and growth inhibition of VSMCs. In contrast, knock down of Nrf2 using an Nrf2 siRNA approach reversed the LNO(2)-induced upregulation of p27(kip1) and inhibition of cellular proliferation in VSMCs. These studies provide the first evidence that nitroalkene LNO(2) inhibits VSMC proliferation through activation of the Keap1/Nrf2 signaling pathway, suggesting an important role of nitroalkenes in vascular biology.

Characterization of the endoevaporitic microbial communities in a hypersaline gypsum crust by fatty acid analysis

We have used fatty acid analyses to study the community structure of a layered endoevaporitic microbial community within a gypsum crust that covers the bottom of a saltern evaporation pond in Eilat, Israel. This community, living at a salinity of 218–238 g l−1 total dissolved salts, consists of an upper brown layer dominated by unicellular cyanobacteria, a green layer with filamentous cyanobacteria, a red-purple layer with both Chromatium and Ectothiorhodospira/Halorhodospira type of purple sulfur bacteria, and a black layer in which dissimilatory sulfate reduction occurs. An olive-green layer is sometimes present below the red-purple layer. Analysis by gas chromatography/mass spectrometry of the fatty acid methyl esters prepared from the different fractions showed characteristic patterns in each layer, and these could be related to fatty acid composition data from the literature and to fatty acid analyses of representative halophilic microorganisms isolated from the site. The nature of the fatty acids in the green layer suggests that the cyanobacteria present there use the oxygen-independent pathway for production of unsaturated fatty acids, a pathway only occasionally encountered in filamentous cyanobacteria. The facultative anaerobic nature of the cyanobacteria in the green layer was confirmed by their ability to perform anoxygenic photosynthesis with sulfide as electron donor. Specific signature fatty acids identified for each layer corresponded well with the microscopic and functional analysis of the biota present.

Physiology and pathophysiology of prostanoid receptors

Prostanoids, consisting of prostaglandins (PGs) and thromboxanes (TXs), are oxygenated products of C20 unsaturated fatty acids. They include PGD2, PGE2, PGF2α, PGI2, and TXA2. Given that aspirin-like nonsteroidal anti-inflammatory drugs exert their actions by suppressing prostanoid production, prostanoids have been implicated in processes inhibited by these drugs, including inflammation, fever, and pain. Prostanoids also contribute to vascular homeostasis, reproduction, and regulation of kidney and gastrointestinal functions. How prostanoids exert such a variety of actions had remained unclear, however. Prostanoids are released outside of cells immediately after their synthesis and exert their actions by binding to receptors on target cells. We have identified a family of eight types or subtypes of G protein–coupled receptors that mediate prostanoid actions. Another G protein–coupled receptor was also identified as an additional receptor for PGD2. Genes for these receptors have been individually disrupted in mice, and analyses of these knockout mice have not only elucidated the molecular and cellular mechanisms of known prostanoid actions but also revealed previously unknown actions. In this article, I review the physiological and pathophysiological roles of prostanoids and their receptors revealed by these studies.(Communicated by Tasuku HONJO, M.J.A.)

Nitrated Fatty Acids as Signaling Molecules

Some fatty acid derivatives, like prostaglandins and thromboxanes, are well known signaling molecules. A more recently recognized, related class of molecules that could have similar functions includes the nitration products of unsaturated fatty acids (nitroalkenes) formed in nitric oxide (NO)-dependent oxidative reactions. In particular, the nitroalkene derivatives of linoleic acid (LNO 2 ) and oleic acid (OA-NO 2 ) are found in human plasma and are thought to regulate physiological functions in multiple cell types. Rather than binding to receptors, though, these molecules are proposed to act by mediating reversible nitroalkylation of glutathione or of Cys or His residues of proteins. Cui et al . now report experiments indicating that LNO 2 and OA-NO 2 may function as antiinflammatory agents. The authors applied concentrations of LNO 2 and OA-NO 2 similar to those found in human blood to cultured mouse macrophages and observed dose-dependent decreases in lipopolysaccharide (LPS)-induced cytokine secretion by the cells. The transcription factor NF-κB has a central role in inflammatory responses, and treatment of macrophages with LNO 2 or OA-NO 2 decreased activation of the transcription factor in response to LPS. Experiments with biotinylated LNO 2 , OA-NO 2 , LA (linoleic acid), and OA indicated that LNO 2 and OA-NO 2 , but not LA or OA, associated with the p65 subunit of NF-κB and appeared to modify p65 by covalent nitroalkylation. The nitroalkenes also inhibited adhesion of monocytes to endothelial cells in culture. The authors propose that nitroalkenes like LNO 2 and OA-NO 2 may prove to be an important class of signaling molecules influencing inflammatory processes. T. Cui, F. J. Schopfer, J. Zhang, K. Chen, T. Ichikawa, P. R. S. Baker, C. Batthyany, B. K. Chacko, X. Feng, R. P. Patel, A. Agarwal, B. A. Freeman, Y. E. Chen, Nitrated fatty acids: Endogenous anti-inflammatory signaling mediators. J. Biol. Chem. 281 , 35686-35698 (2006). [Abstract] [Full Text]

Nitrated Fatty Acids: Endogenous Anti-inflammatory Signaling Mediators

Nitroalkene derivatives of linoleic acid (LNO2) and oleic acid (OA-NO2) are present; however, their biological functions remain to be fully defined. Herein, we report that LNO2 and OA-NO2 inhibit lipopolysaccharide-induced secretion of proinflammatory cytokines in macrophages independent of nitric oxide formation, peroxisome proliferator-activated receptor-gamma activation, or induction of heme oxygenase-1 expression. The electrophilic nature of fatty acid nitroalkene derivatives resulted in alkylation of recombinant NF-kappaB p65 protein in vitro and a similar reaction with p65 in intact macrophages. The nitroalkylation of p65 by fatty acid nitroalkene derivatives inhibited DNA binding activity and repressed NF-kappaB-dependent target gene expression. Moreover, nitroalkenes inhibited endothelial tumor necrosis factor-alpha-induced vascular cell adhesion molecule 1 expression and monocyte rolling and adhesion. These observations indicate that nitroalkenes such as LNO2 and OA-NO2, derived from reactions of unsaturated fatty acids and oxides of nitrogen, are a class of endogenous anti-inflammatory mediators.

Oxylipin Profiling of the Hypersensitive Response in Arabidopsis thaliana: FORMATION OF A NOVEL OXO-PHYTODIENOIC ACID-CONTAINING GALACTOLIPID, ARABIDOPSIDE E

Oxylipin Profiling of the Hypersensitive Response in Arabidopsis thaliana: FORMATION OF A NOVEL OXO-PHYTODIENOIC ACID-CONTAINING GALACTOLIPID, ARABIDOPSIDE E

Oxylipin Profiling of the Hypersensitive Response inArabidopsis thaliana

Oxidation products of unsaturated fatty acids, collectively known as oxylipins, function as signaling molecules in plants during development, wounding, and insect and pathogen attack. Certain oxylipins are also known to have direct cytotoxic effects on pathogens. We used inducible expression of bacterial avirulence proteins in planta to study the involvement of oxylipins in race-specific defense against bacterial pathogens. We demonstrate that recognition of the Pseudomonas syringae avirulence protein AvrRpm1 induces 9- and 13-lipoxygenase-dependent oxylipin synthesis in Arabidopsis thaliana. The major oxylipins accumulated were jasmonic acid, 12-oxo-phytodienoic acid, and dinor-oxo-phytodienoic acid. The majority of the newly formed oxylipins (>90%) was found to be esterified to glycerolipids, whereby 12-oxo-phytodienoic acid and dinor-oxo-phytodienoic acid were found to be esterified to a novel galactolipid. The structure of the substance was determined as a monogalactosyldiacylglycerol containing two 12-oxo-phytodienoic acids and one dinor-oxo-phytodienoic acid acyl chain and was given the trivial name arabidopside E. This substance accumulated to surprisingly high levels, 7-8% of total lipid content, and was shown to inhibit growth of a bacterial pathogen in vitro. Arabidopside E was formed also after recognition of the avirulence protein AvrRpt2, suggesting that this could be a conserved feature of defense reactions against bacterial pathogens. In conclusion, the data presented suggest a role of enzymatically formed oxylipins, especially the octadecanoids and arabidopside E in race-specific resistance against bacterial pathogens.

Regulation of fatty acid composition of Escherichia coli membrane by FabA and FabZ

The role of the two dehydratases in type Ii fatty acid biosynthesis, FabA and FabZ, in unsaturated fatty acid (UFA) biosynthesis was investigated by expressing wild-type and two dominate-negative mutants FabA[H70A, D84A] (FabAdb) and FabZ[H54A, E68A] (FabZdb) to increase or knock down their enzyme activity. Protein expression was varied using an arabinose-inducible promoter and the effects were evaluated by metabolic labeling. Increasing FabZ activity reduced UFA production, whereas the FabZ knock down increased UFA formation. Increasing FabA activity decreased UFA synthesis, whereas expression of the dominant-negative FabAdb decreased UFA synthesis and eventually suppressed all fatty acid synthesis. Thus, the elimination of FabA activity with the dominant negative construct was different that the selective inhibition of UFA production observed when the protein activity was eliminated in the fabA mutant. Virtually all the cellular acyl carrier protein (ACP) was found in complex with FabAdb when cell lysates were analyzed by western blot with anti-FabAdb and anti-ACP antibodies. The ACP was purified from these complexes and electrophoretic analysis and mass spectroscopy identified them as acyl-ACPs with chain lengths between 8 to 12 carbons, with β-hydroxy-decanoyl-ACP, the known substrate for FabA, being the most abundant. These results show that FabAdb blocked fatty acid synthesis by sequestering acyl-ACP from processing by other enzymes in the pathway. (Supported by GM 34496)

An acyl-CoA dehydrogenase is involved in the formation of the Δcis3 double bond in the acyl residue of the lipopeptide antibiotic friulimicin in Actinoplanes friuliensis

The lipopeptide antibiotic friulimicin, produced by Actinoplanes friuliensis, is an effective drug against Gram-positive bacteria, such as methicillin-resistant Staphylococcus epidermidis and Staphylococcus aureus strains. Friulimicin consists of a cyclic peptide core of ten amino acids and an acyl residue linked to an exocyclic amino acid. The acyl residue is essential for antibiotic activity, varies in length from C13 to C15, and carries a characteristic double bond at position Delta cis3. Sequencing of a DNA fragment adjacent to a previously described fragment encoding some of the friulimicin biosynthetic genes revealed several genes whose gene products resemble enzymes of lipid metabolism. One of these genes, lipB, encodes an acyl-CoA dehydrogenase homologue. To elucidate the function of the LipB protein, a lipB insertion mutant was generated and the friulimicin derivative (FR242) produced by the mutant was purified. FR242 had antibiotic activity lower than friulimicin in a bioassay. Gas chromatography showed that the acyl residue of wild-type friulimicin contains a double bond, whereas a saturated bond was present in FR242. These results were confirmed by the heterologous expression of lipB in Streptomyces lividans T7, which led to the production of unsaturated fatty acids not found in the S. lividans T7 parent strain. These results indicate that the acyl-CoA dehydrogenase LipB is involved in the introduction of the unusual Delta cis3 double bond into the acyl residue of friulimicin.

Improving the Fatty Acid Profile of Fairy Shrimp, Streptocephalus dichotomus, Using a Lipid Emulsion Rich in Highly Unsaturated Fatty Acids

Fatty acids are the largest component of lipids and have become a useful tool in the determination of live feeds to a variety of cultured species. Bioencapsulation is a technique which allows high-level incorporation of desired components (i.e., fatty acids, vitamins, antibiotics, etc.) in live feeds, which in turn can be supplemented to the consumer organisms. The procedure described in the present study serves as a platform of technology for enriching the Streptocephalus dichotomus. Uptake of two enrichment diets (ALGAMAC2000 and DHA-SELCO) by adult S. dichotomus was investigated. The fatty acid profile supports the hypothesis that the enrichment diet increases the level of essential fatty acids, such as linolic, linolenic, eicosapentenoic, and docosahexaenoic acids. The average content (percent of total fatty acids detected) of the enriched organism by different highly unsaturated fatty acid (HUFA) products were as follows: ALGAMAC2000 showed 14-22% saturated fatty acid (SFA), 17-18% monounsaturated fatty acid (MUFA), 28-41% polyunsaturated fatty acid (PUFA), 23-34% n-3, and 4.9-7.5% n-6, whereas DHA-SELCO showed about 20-23% SFA, 20-26% MUFA, 38% PUFA, 28-31% n-3, and 7.5-10% n-6. Our present investigation proves that both HUFA-rich diets appear to be an appropriate enrichment diet, and further provides an additional rationale for using fairy shrimp as a maturation diet for any cultivable freshwater organism.

Characterisation of organic residues in pottery vessels of the Roman age from Antinoe (Egypt)

In the framework of a study on the Egyptian ceramic vessels belonging to the archaeological collection of the Istituto Papirologico Vitelli (Florence), the characterisation of organic residues from three findings of the 5th–7th centuries A.D. has been performed. The materials were identified by two analytical procedures based on Fourier transformed infrared spectroscopy (FTIR) and on gas chromatography coupled with mass spectrometry (GC–MS), respectively. The first procedure is suitable for detecting the functional groups of organic substances and thus for distinguishing them; the second permits the simultaneous analysis of several natural substances such as vegetable resins and oils, bitumen, tar and pitch, and waxes. The presence of monocarboxylic acids, α,ω-dicarboxylic acids, long-chain dihydroxylated acids, and terpenic species, highlights that although the organic residues showed a high heterogeneity in composition, they mainly consisted of materials of vegetable origin. In particular, the presence of oxidation products of characteristic unsaturated fatty acids suggests the occurrence of oil produced from plant seeds of the Cruciferae family, some of which are reported to have been used in ancient Egypt to produce oil. Moreover, the presence of characteristic diterpenic biomarkers in two of the three pieces of pottery enables us to assess the use of both pine resin and pine pitch.

Two Δ9-stearic acid desaturases are required for Aspergillus nidulans growth and development

Unsaturated fatty acids are important constituents of all cell membranes and are required for normal growth. In the filamentous fungus Aspergillus nidulans, unsaturated fatty acids and their derivatives also influence asexual (conidial) and sexual (ascospore) sporulation processes. To investigate the relationship between fatty acid metabolism and fungal development, we disrupted the A. nidulans sdeA and sdeB genes, both encoding Δ9-stearic acid desaturases responsible for the conversion of palmitic acid (16:0) and stearic acid (18:0) to palmitoleic acid (16:1) and oleic acid (18:1). The effects of sdeA deletion on development were profound, such that growth, conidial and ascospore production were all reduced at 22 and 37 °C. Total fatty acid content was increased over 3-fold in the Δ sdeA strain, reflected in up-regulation of the expression of the fasA gene encoding the α chain of the fatty acid synthase, compared to wild type. Stearic acid accumulated approximately 3-fold compared to wild type in the Δ sdeA strain, while unsaturated fatty acid production was decreased. In contrast, disruption of sdeB reduced fungal growth and conidiation at 22 °C, but did not affect these processes at 37 °C compared to wild type. Interestingly, ascospore production was increased at 37 °C for Δ sdeB compared to wild type. Total fatty acid content was not increased in this strain, although stearic acid accumulated 2-fold compared to wild type, and unsaturated fatty acid production was decreased. Combining the Δ sdeA and Δ sdeB alleles created a synthetic lethal strain requiring the addition of oleic acid to the medium for a modicum of growth. Taken together, our results suggest a role for sdeA in growth and development at all temperatures, while sdeB is involved in growth and development at lower temperatures.

Cis-3-Hexenal production in tobacco is stimulated by 16-carbon monounsaturated fatty acids

Transgenic tobacco plants O9 and T16 expressing the yeast acyl-CoA Δ9 desaturase and an insect acyl-CoA Δ11 desaturase, respectively, displayed altered profiles of fatty acids compared to wild-type tobacco plants and marked increases in cis-3-hexenal, a major leaf volatile derived from α-linolenic acid (18:3). As expected, O9 and T16 plants had increased levels of the major unsaturated fatty acid products formed by the transgenic desaturases they expressed, viz., palmitoleic acid (16:1 Δ9) and palmitvaccenic acid (16:1 Δ11), respectively. In addition, levels of 18:3 lipid declined slightly and the pool of free 18:3, which accounts for about 30% of free fatty acids in wild-type plants, disappeared completely in both transgenics. Both O9 and T16 plants were found to have a two-fold increase in 13-lipoxygenase (13-LOX) activity, which catalyzes the first of two steps leading to hexenal production from 18:3. In O9 and T16 plants, the activity of 9-lipoxygenase and hydroperoxide lyase, the latter catalyzing the formation of cis-3-hexenal from α-linolenic acid hydroperoxide, was significantly different from that of the wild-type plants. Although 16:1 Δ9 and 16:1 Δ11 had no direct effects on 13-LOX activity in vitro, cis-3-hexenal production increased in tobacco leaves treated with these fatty acids, suggesting that they may act in vivo by stimulating 13-LOX gene expression.

Biological functions of group X secretory PLA2.

Secretory phospholipase A2s (sPLA2s) are a diverse family of low molecular mass enzymes that hydrolyze the sn-2 fatty acid ester bond of glycerophospholipids to produce free fatty acids and lysophospholipids. In addition to the classical types of group IB and IIA (sPLA2-IB and IIA), recent advances in molecular biology have led to the identification of novel types of sPLA2s, including group IID and IIE that we have cloned [1]. Among the nine types of human sPLA2s, group X sPLA2 (sPLA2-X) has a structural similarity with the classical type of sPLA2-IB and IIA [2]. We have shown that sPLA2-X has a potent hydrolyzing activity toward phosphatidylcholine (PC) and elicits more potent production of unsaturated fatty acids and lysophosphatidylcholine (lysoPC) in various inflammatory cells and colon cancer cells compared with sPLA2-IB and IIA [3,4]. The released arachidonic acid by sPLA2-X was efficiently converted to prostaglandins (PGs) by the action of endogenous cyclooxygenase (COX). The expression of sPLA2-X was detected in human lung epithelial cells and mouse splenic macrophages, and greatly augmented in human colon adenocarcinoma tissues in concert with enhanced expression of COX-2 [4]. These findings suggest that sPLA2-X plays a critical role in the lipid mediator productions under various inflammatory states and in the COX-2- dependent PGE2 biosynthesis during colon tumorigenesis. Recently, we have shown that sPLA2-X is a high-affinity ligand for mouse PLA2 receptor (PLA2R) and identified a soluble PLA2R in mouse plasma [5]. Using PLA2 receptor-deficient mice, we have shown that the membrane and soluble form of the receptor are involved in the endogenous inhibitory mechanisms against the strong PC-hydrolizing activity of sPLA2-X in mice [5].

The FabR (YijC) Transcription Factor Regulates Unsaturated Fatty Acid Biosynthesis in Escherichia coli

Unsaturated fatty acid biosynthesis is a vital facet of Escherichia coli physiology and requires the expression of two genes, fabA and fabB, in the type II fatty acid synthase system. This study links the FabR (YijC) transcription factor to the regulation of unsaturated fatty acid content through the regulation of fabB gene expression. The yijC (fabR) gene was deleted by replacement with a selectable cassette, and the resulting strains (fabR::kan) possessed significantly elevated levels of unsaturated fatty acids, particularly cis-vaccenate, in their membrane phospholipids. The altered fatty acid composition was observed in the fabR::kan fabF1 double mutant pinpointing fabB as the condensing enzyme responsible for the increased cis-vaccenate production. The fabR::kan strains had 4- to 8-fold higher levels of fabB and a 2- to 3-fold increase in fabA transcripts as judged by Northern blotting, Affymetrix array analysis, and real-time PCR. FabR did not regulate the enzymes of fatty acid beta-oxidation. The elevated level of fabB mRNA was reflected by higher condensing enzyme activity in fabR::kan fabF1 double mutants. Thus, FabR functions as a repressor that potently controls the expression of the fabB gene, which in turn, modulates the physical properties of the membrane by altering the level of unsaturated fatty acid production.