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 Acids and Lipids Biosynthesis → 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 palmityl (16:0) and oleoyl (18:1) acyl groups, the products of the 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.
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 acyl-CoA synthetase. The oleoyl-CoA is incorporated into lipids, forming a 1,2-diacyl-sn-glycerol 3-phosphate, a diglyceride, and a phosphatidylcholine. Further desaturation of the oleoyl groups to linoleoyl groups in the ER occurrs while incorporated into lipids, and is catalyzed by the fatty acyl Δ15 desaturase (endoplasmic reticulum), encoded by the FAD2 gene.
A smaller portion of the oleoyl-[acp] molecules can be incorporated into a 1,2-diacyl-sn-glycerol 3-phosphate and a diglyceride within the chloroplast. In this case, the desaturation to a lipid linoleoyl group occurs by a plastidic desaturase, 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)
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
Malhotra99: Malhotra KT, Malhotra K, Lubin BH, Kuypers FA (1999). "Identification and molecular characterization of acyl-CoA synthetase in human erythrocytes and erythroid precursors." Biochem J 344 Pt 1;135-43. PMID: 10548543
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
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
Rubio06: Rubio S, Larson TR, Gonzalez-Guzman M, Alejandro S, Graham IA, Serrano R, Rodriguez PL (2006). "An Arabidopsis mutant impaired in coenzyme A biosynthesis is sugar dependent for seedling establishment." Plant Physiol 140(3);830-43. PMID: 16415216
Schnurr02: Schnurr JA, Shockey JM, de Boer GJ, Browse JA (2002). "Fatty acid export from the chloroplast. Molecular characterization of a major plastidial acyl-coenzyme A synthetase from Arabidopsis." Plant Physiol 129(4);1700-9. PMID: 12177483
Shockey02: Shockey JM, Fulda MS, Browse JA (2002). "Arabidopsis contains nine long-chain acyl-coenzyme a synthetase genes that participate in fatty acid and glycerolipid metabolism." Plant Physiol 129(4);1710-22. PMID: 12177484
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