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MetaCyc Pathway: linoleate biosynthesis I (plants)
Inferred from experiment

Enzyme View:

Pathway diagram: linoleate biosynthesis I (plants)

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: BiosynthesisFatty Acid and Lipid BiosynthesisFatty Acid BiosynthesisUnsaturated Fatty Acid BiosynthesisLinoleate 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

General Background

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, 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, 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].

Variants: linoleate biosynthesis II (animals), linoleate biosynthesis III (cyanobacteria)

Created 05-Aug-2008 by Caspi R, SRI International
Revised 07-Nov-2014 by Caspi R, SRI International


Schmidt90: Schmidt H, Heinz E (1990). "Desaturation of oleoyl groups in envelope membranes from spinach chloroplasts." Proc Natl Acad Sci U S A 87(23);9477-80. PMID: 11607123

Other References Related to Enzymes, Genes, Subpathways, and Substrates of this Pathway

Bi13: Bi H, Wang H, Cronan JE (2013). "FabQ, a dual-function dehydratase/isomerase, circumvents the last step of the classical fatty acid synthesis cycle." Chem Biol 20(9);1157-67. PMID: 23972938

Biebl02: Biebl H, Sproer C (2002). "Taxonomy of the glycerol fermenting clostridia and description of Clostridium diolis sp. nov." Syst Appl Microbiol 25(4);491-7. PMID: 12583708

Broun98: Broun P, Boddupalli S, Somerville C (1998). "A bifunctional oleate 12-hydroxylase: desaturase from Lesquerella fendleri." Plant J 13(2);201-10. PMID: 9680976

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

Johnston83: Johnston NC, Goldfine H (1983). "Lipid composition in the classification of the butyric acid-producing clostridia." J Gen Microbiol 129(4);1075-81. PMID: 6886674

Kumar12: Kumar R, Tran LS, Neelakandan AK, Nguyen HT (2012). "Higher plant cytochrome b5 polypeptides modulate fatty acid desaturation." PLoS One 7(2);e31370. PMID: 22384013

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

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."

Lederer94: Lederer F (1994). "The cytochrome b5-fold: an adaptable module." Biochimie 76(7);674-92. PMID: 7893819

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

Miquel93: Miquel M, James D, Dooner H, Browse J (1993). "Arabidopsis requires polyunsaturated lipids for low-temperature survival." Proc Natl Acad Sci U S A 90(13);6208-12. PMID: 11607410

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

Ohlrogge95: Ohlrogge J, Browse J (1995). "Lipid biosynthesis." Plant Cell 7(7);957-70. PMID: 7640528

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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Report Errors or Provide Feedback
Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by Pathway Tools version 19.5 (software by SRI International) on Sat Apr 30, 2016, biocyc11.