These estolides have anti-diabetic and anti-inflammatory effects, even when administered orally, and they protect against colitis by regulating gut innate and adaptive immune responses. In addition, they may have an important role in maintaining normal blood sugar levels and insulin sensitivity by acting as selective agonists for the GPR40 receptor. In contrast, there is a suggestion that esterification of 9-hydroxy-octadecanoic acid in tumors may be an escape mechanism to minimize the risk of apoptosis.
The linoleic acid ester of hydroxy linoleic acid LAHLA derived from oat oil has been shown to be an anti-inflammatory lipid, which suppresses lipopolysaccharide-stimulated secretion of cytokines and the expression of pro-inflammatory genes. While most of these are not derived from the essential fatty acids, others have been found in adipose tissue with docosahexaenoic acid DHA esterified to 9- and hydroxyoctadecadienoic and hydroxydocosahexaenoic acids; they are present at concentrations similar to those of the specialized pro-resolving mediators and have profound anti-inflammatory effects.
Little is known of the biosynthesis of these lipids, but it has been established that they are produced endogenously with defined stereochemistry, i. Fatty acids with esterified hydroxyl groups in either the 2- or terminal position are components of di- and triesters from meibomian glands of some animal species. Triacylglycerol estolides are present in the paracloacal gland of the brushtail possum with an or hydroxy fatty acid component.
The skin from animals, but studied especially in pigs and humans, contains O -acyl ceramides in which a long-chain fatty acid component up to C 36 has a terminal hydroxyl group, which may be in the free form or esterified with linoleic acid see the web page on Ceramides for a detailed discussion of the structures, biosynthesis and functions of these lipids. These ceramides eventually lose the estolide fatty acid and link directly via the terminal hydroxyl group to structural proteins, as vital components of the epidermal permeability barrier.
Estolides have long been known as components of seed oils and fungi, and some examples are described below. Bees and many other insect species produce lactonized hydroxy fatty acids as pheromones or simply for recognition by their kin. Many other insect waxes and secretions contain hydroxy fatty acids, and perhaps the best known of these is the insect Tachardia Laccifer lacca , which produces the polymeric material shellac.
Note that the stereochemistry of adjacent hydroxyl groups in the figure is defined from that of the sugars threose and erythrose with threo -dihydroxyls on opposite sides of the alkyl-chain, while erythro groups are on the same side. These act as potent chemical deterrents to larval predators such as ants. As in animal tissues, 2- R -hydroxy fatty acids occur in appreciable amounts in the sphingolipids of plants.
Other 2-hydroxy acids may be encountered in seed oils. For example, 2-hydroxy-octadeca-9,12,trienoate is a minor component of the seed oil of Thymus vulgaris , 2-hydroxy-oleic and linoleic acids are found in Salvia nilotica , and 2-hydroxy-sterculic acid is occasionally encountered in seed oils of the Malvales. The seed oils of higher plants contain a number of hydroxy acids, some of which are important agricultural commodities. Biosynthesis occurs via the action of an oleate hydroxylase, an enzyme closely related structurally to a fatty acyl desaturase.
The homologous hydroxy-eicos- cis enoic lesquerolic acid is a component of seed oils from the genus Lesquerella, while the isomeric 9-hydroxy-octadeca- cis enoic isoricinoleic acid is found in the genus Strophanthus. Other non-conjugated dienoic fatty acids, which appear to be related biosynthetically to these monoenes have been reported in seed oils, and include hydroxy-octadeca- cis -9, cis dienoic densipolic and hydroxy-eicosa- cis , cis dienoic auricolic acids. Among many others, hydroxylinoleate and an estolide of this acid have been isolated from the seeds of oats Avena sativa , while 7,dihydroxy-tetracosenoic nebraskanic acid has been characterized from the seed oil of the Chinese violet cress Orychophragmus violaceus.
The latter is of special interest in that the sequence of chain-length elongation reactions in biosynthesis is interrupted in a manner usually seen only with bacterial fatty acids; this and a related fatty acid, wuhanic acid, are present in the oil as estolides in addition to the link to glycerol. Similar lipids to the FAHFA found in animal tissues have been found in a variety of plant species, with stearic acid hydroxy stearic acid often the most abundant form.
Their functions in plants are not known.
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Conjugated dienoic fatty acids with a hydroxyl group are also known from a number of seed oils, and some may have commercial importance. Almost all are C 18 in chain-length. These include 9-hydroxy-octadeca- trans , trans dienoic dimorphecolic acid from the seed oil of Dimorphotheca sinuata , while the geometrical isomer with a cis -double bond in position 12 is present in the seed oil of Calendula officinalis among others.
Further conjugated hydroxy-fatty acids have acetylenic bonds, including ximenynolic 8-hydroxy,9a,11 t and isanolic 8-hydroxy,9a,11a,17e acids. Dihydroxy acids, such as 9,dihydroxy-octadecanoic acid and higher homologues, can be minor components of several seed oils, including castor oil, but they occur in significant concentrations in the seed oil of Cardamine impatiens.
Cutin and suberin: The aerial surfaces of higher plants are covered with a continuous extracellular layer, termed the cuticle that contains cutin as the major structural component. Suberin is a related but distinct material that forms near the plasma membrane in the plant cells of the periderm, i. The function of these layers is to act as barriers to control the movement of gases, water and solutes, and to impart resistance to pathogens or herbivores.
They are distinct from the waxy coating that covers the external surface see our web page on waxes and indeed act as a support for it. In cutin, these fatty acids have chain lengths of 16 and 18 carbons, while suberin is much more complex as the range of chain-lengths can go up to C Suberins contain similar fatty acids but with a wider range of chain-lengths and varying degrees of oxygenation.
For example, oleic acid is believed to be the biosynthetic precursor of hydroxy-oleic, 9,10,trihydroxy-octadecanoic, 1,octadecenedioic and 9,dihydroxy-1,octadecanedioic acids, together with 9,epoxy analogues. Phenolic acids, such as ferulic, are also incorporated into the polymer. The best-known and characterized source of suberin is cork, derived from the bark of the cork oak Quercus suber , and the cutin of the 'model' plant Arabidopsis thaliana has also been analysed and it appears to be similar to that of many other species.
During biosynthesis, a hydroxyl group is introduced first at the terminal carbon atom of an existing fatty acid by means of cytochrome Pdependent fatty acid monooxygenases, and this can then be converted to a dicarboxylic acid by a fatty acid oxygenase. Long-chain acyl-coenzyme A synthetases and acyltransferases G3P acyltransferase GPAT are then required for the synthesis of the complex polymer.
Fungal Lipid Biochemistry | SpringerLink
In bacterial lipopolysaccharides, the 2-hydroxyl group has the S -configuration in contrast to that in animals and plants. As such they are often found in environmental samples, like soils, biofilms or sediments. Fatty acids of this kind are usually saturated, in some instances with iso - or anteiso -methyl branches, but monoenes are occasionally found. The fatty acids can be linked by both ester and amide bonds to glucosamine or other amino-sugars in these lipids. Most fatty acids of this type tend to be fully saturated, sometimes with iso - or anteiso -methyl branches. Mycolic acids , discussed elsewhere in the pages, also contain a hydroxyl group in position 3, and can have keto and methoxyl groups elsewhere in the chain.
Many bacterial species produce fatty acid lactones as signalling molecules, and for example, Streptomycetes species use a family of lactones termed butanolides to regulate their production of secondary metabolites. Currently, these are of considerable interest to industry as a source of biodegradable polymers, substituting for petroleum-derived plastics. Copolymers with 3-hydroxy-valerate or with C 5 to C 14 3-hydroxyalkanoate units are also known from various bacterial species.
The former can be produced by a number of bacterial species, including lactic acid bacteria, from oleic acid added to the growth medium, and it is a major component of the lipids of the protozoon Cryptosporidium parvum.
A number of microbial reactions of this type that produce saturated and unsaturated hydroxy and keto acids are being studied as the products may have potential industrial value. Some bacterial species are capable of hydroxylating fatty acids close to the terminal part of the molecule. For example, preparations from Bacillus megaterium are able to convert palmitic acid to hydroxypalmitate mainly, although and hydroxypalmitate are also produced. The actions of gut microorganisms to produce hydroxy fatty acids that affect the metabolism of their host are discussed briefly above.
In yeasts and fungi, 2-hydroxy fatty acids are major constituents of sphingolipids amide linked as in plants and animals. In some species of fungi, there is an additional trans double bond in position 3, while 2,3-dihydroxy fatty acids have been reported from yeasts. Unusual fatty acids with hydroxyl groups in central positions, together with methyl groups and double bonds, occur in species of fungi, lichens and slime moulds. For example, 7-hydroxy-8,dimethylhexadecenoic acid, and structurally related fatty acids, were found in fungal species belonging to the Ascomycetes and Basidiomycetes.
Ricinoleic acid, the main component of castor oil, is also a major component of the lipids of the fungus ergot Claviceps purpurea , where it is found esterified to glycerol in triacylglycerols, and these may be linked to further ricinoleate molecules via ester bonds, i. The biosynthetic pathway differs from that in the castor oil plant in that linoleic acid is the substrate and hydroxylation occurs under anaerobic conditions, i. Epoxy fatty Acids : cis -9,Epoxy-octadecanoic acid has been detected and quantified in plasma of humans, and it is believed to be formed by epoxidation of the double bond of oleic acid by a cytochrome P enzyme.
Its physiological function and fate are not known. Similar mono-epoxy fatty acids are formed in lung and other tissues from linoleate and termed leukotoxins the term includes a range of diverse compounds , because they produce their primary toxic effects against leukocytes. Together with dihydroxy metabolites formed on ring opening, they are believed to have unpleasant cardiovascular effects and to be involved in acute respiratory distress syndrome, especially in burn patients. Epoxidized polyunsaturated fatty acids are discussed in our web pages dealing with eicosanoid metabolism.
Frank Gunstone found the first natural epoxy fatty acid, i. In this instance, the stereochemistry of the epoxyl group was shown to be was shown to be 12 S ,13 R , but the optical antipode, - -vernolic acid, has been isolated from certain seed oils of the Malvaceae. Subsequently, the isomeric cis -9,epoxy-octadec- cis enoic 'coronaric' acid, cis ,epoxy-octadeca- cis -9,dienoic acid, and cis -9,epoxy-octadecanoic were found in seed oils.
Lipid production in association of filamentous fungi with genetically modified cyanobacterial cells
Biosynthesis involves an epoxygenase enzyme, closely related in structure to desaturases. On prolonged storage, small amounts of epoxy or hydroxy acids of defined stereochemistry are generated by enzymic processes in many different seed oils. Vernolic and coronaric acids have an obvious biosynthetic relationship to linoleic acid.
Saturated epoxy fatty acids, such as 9,epoxy-octadecanoic and 9,epoxy,hydroxy-octadecanoate acids, are found in plant cutins see above. Furanoid fatty acids with the general structural formula illustrated are minor but widespread components of plant lipids. However, interest in these compounds was stimulated by the discovery that they were present at low levels in fish, especially in their reproductive tissues, although they are presumed to originate in the diet. Subsequently, they were found in other animal products, especially dairy products where they presumably come from the diet of the herbivores, and even in human plasma and erythrocytes.
At least 23 different furanoid fatty acids have now been detected in fish lipids, including some with 1 or 2 additional double bonds in positions outwith the ring. They can amount to 0. In fish, furanoid fatty acids occur in triacylglycerols and cholesterol esters, especially the latter where they can occur in higher concentrations than the conventional fatty acids. Other marine sources include sponges and soft corals. In human and bovine plasma, they are present mainly in phospholipids.
Similar fatty acids have been found in a variety of plant sources. For example, in the latex of the rubber tree Hevea brasiliensis , 10,epoxymethyloctadeca,dienoic acid has been identified as the main component of the lipid fraction, and this and other furanoid fatty acids have been detected as minor components in numerous other plants seeds, leaves and fruit in amounts comparable to the tocopherols, i.
Indeed, it is suggested that plants, algae and bacteria via the food chain are the main source of furanoid fatty acids in animals and fish, especially for the pentyl-substituted fatty acids and those with double bonds in the terminal part of the chain. Linoleic acid is the biosynthetic precursor of the more abundant furanoid fatty acids with the methyl substituents derived from adenosylmethionine.
While the origin of the propyl-substituted compounds is less certain, they may be derived from metabolism of 9,hexadecadienoic acid in algae such as Phaeodactylum tricornutum. UniBible has again political to community and management, agreement of Biola University.
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