This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Fatty Acid and Lipid Biosynthesis → Fatty Acid Biosynthesis → Unsaturated Fatty Acid Biosynthesis → Linoleate Biosynthesis|
Some taxa known to possess this pathway include : Arabidopsis thaliana col, Brassica juncea, Carthamus tinctorius, Glycine max, Linum usitatissimum, Oryza sativa, Sesamum indicum, Spinacia oleracea, Thunbergia alata
Expected Taxonomic Range: Viridiplantae
linoleate is a polyunsaturated fatty acid that is abundant in many vegetable oils, especially safflower and sunflower oils. It is an essential dietary requirement for all mammals, that lack the Δ12 desaturase that produces it. A few animals are able to synthesize linoleate, as described in linoleate biosynthesis II (animals).
Linoleate is an ω-6 fatty acid, referring to the position of the first double bond from the methyl end of the fatty acid.
In all plant tissues, the major glycerolipids are first synthesized using only palmitoyl (16:0) and oleoyl (18:1) acyl groups, the products of plastidic saturated fatty acid synthesis (see palmitate biosynthesis II (bacteria and plants), stearate biosynthesis II (bacteria and plants) and oleate biosynthesis I (plants)). Subsequent desaturation of the fatty acids to the highly unsaturated forms typical of the membranes of plant cells is carried while they are already attached to lipids.
About This Pathway
Most of the oleoyl-[acp] is released from the [acp]-moiety and exported from the plastid to the endoplasmic reticulum (ER), and is converted to oleoyl-CoA in the process by the plastidic long-chain acyl-CoA synthetase 9. The oleoyl-CoA is incorporated into lipids, forming phosphatidylglycerols, diglycerides, and phosphatidylcholines. Further desaturation of the oleoyl groups to linoleoyl groups in the ER occurrs while incorporated into lipids, and is catalyzed by EC 188.8.131.52, acyl-lipid ω-6 desaturase (cytochrome b5)|, encoded by the FAD2 gene.
A smaller portion of the oleoyl-[acp] molecules can be incorporated into phosphatidylglycerols and diglycerides within the chloroplast. In this case, the desaturation to a [glycerolipid]-linoleate occurs by a plastidic desaturase ( EC 184.108.40.206, acyl-lipid (n+3)-(Z)-desaturase (ferredoxin)), which is encoded by the FAD6 gene. Envelope membranes isolated from chloroplasts of spinach ( Spinacia oleracea) could desaturate oleoyl groups in monogalactosyl diacylglycerol to linoleoyl groups. The desaturation required NADPH in combination with ferredoxin, and was also observed with other biosynthetic intermediates such as phosphatidates [Schmidt90].
Browse93: Browse J, McConn M, James D, Miquel M (1993). "Mutants of Arabidopsis deficient in the synthesis of alpha-linolenate. Biochemical and genetic characterization of the endoplasmic reticulum linoleoyl desaturase." J Biol Chem 1993;268(22);16345-51. PMID: 8102138
Covello96: Covello PS, Reed DW (1996). "Functional expression of the extraplastidial Arabidopsis thaliana oleate desaturase gene (FAD2) in Saccharomyces cerevisiae." Plant Physiol 1996;111(1);223-6. PMID: 8685264
Falcone94: Falcone DL, Gibson S, Lemieux B, Somerville C (1994). "Identification of a gene that complements an Arabidopsis mutant deficient in chloroplast omega 6 desaturase activity." Plant Physiol 1994;106(4);1453-9. PMID: 7846158
Goldfine71: Goldfine H, Panos C (1971). "Phospholipids of Clostridium butyricum. IV. Analysis of the positional isomers of monounsaturated and cyclopropane fatty acids and alk-1'-enyl ethers by capillary column chromatography." J Lipid Res 12(2);214-20. PMID: 5554109
Huang99b: Huang YS, Chaudhary S, Thurmond JM, Bobik EG, Yuan L, Chan GM, Kirchner SJ, Mukerji P, Knutzon DS (1999). "Cloning of delta12- and delta6-desaturases from Mortierella alpina and recombinant production of gamma-linolenic acid in Saccharomyces cerevisiae." Lipids 34(7);649-59. PMID: 10478922
Jaworski74: Jaworski JG, Stumpf PK (1974). "Fat metabolism in higher plants. Properties of a soluble stearyl-acyl carrier protein desaturase from maturing Carthamus tinctorius." Arch Biochem Biophys 162(1);158-65. PMID: 4831331
Lager13: Lager I, Yilmaz JL, Zhou XR, Jasieniecka K, Kazachkov M, Wang P, Zou J, Weselake R, Smith MA, Bayon S, Dyer JM, Shockey JM, Heinz E, Green A, Banas A, Stymne S (2013). "Plant acyl-CoA:lysophosphatidylcholine acyltransferases (LPCATs) have different specificities in their forward and reverse reactions." J Biol Chem 288(52);36902-14. PMID: 24189065
Mekhedov00: Mekhedov S, de Ilarduya OM, Ohlrogge J (2000). "Toward a functional catalog of the plant genome. A survey of genes for lipid biosynthesis." Plant Physiol 2000;122(2);389-402. PMID: 10677432
Miquel92: Miquel M, Browse J (1992). "Arabidopsis mutants deficient in polyunsaturated fatty acid synthesis. Biochemical and genetic characterization of a plant oleoyl-phosphatidylcholine desaturase." J Biol Chem 267(3);1502-9. PMID: 1730697
Napier03: Napier JA, Michaelson LV, Sayanova O (2003). "The role of cytochrome b5 fusion desaturases in the synthesis of polyunsaturated fatty acids." Prostaglandins Leukot Essent Fatty Acids 68(2);135-43. PMID: 12538077
Okuley94: Okuley J, Lightner J, Feldmann K, Yadav N, Lark E, Browse J (1994). "Arabidopsis FAD2 gene encodes the enzyme that is essential for polyunsaturated lipid synthesis." Plant Cell 6(1);147-58. PMID: 7907506
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