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MetaCyc Enzyme: acyl-lipid ω-6 desaturase

Gene: FAD2 Accession Number: AT3G12120 (MetaCyc)

Synonyms: At3g12120, oleate desaturase, oleate Δ12 desaturase, ω-6 oleate desaturase, acyl-lipid 12-desaturase, endoplasmic reticulum

Species: Arabidopsis thaliana col

Subunit composition of acyl-lipid ω-6 desaturase = [FAD2]
         ω-6 fatty acid desaturase, endoplasmic reticulum = FAD2

Summary:
The FAD2 desaturase, which is located at the endoplasmic reticulum (ER), introduces a second double bond (Δ12) in oleate incorporated into phosphatidylcholine, an important extra-plastidial membrane lipid, converting it into linoleate [Browse93].

The enzyme is an ω6 desaturase, which means it introduces the double bond at a location 6 carbons away from the methyl end of the fatty acid. The distance from the carboxylic acid end of the molecule does not affect the location of the new double bond.

Like other desaturases located in the endoplasmic reticulum, the enzyme utilizes a cytochrome b5 as the electron donor [Ohlrogge95]. While the FAD2 gene does not include a cytochrome b5 domain, the enzyme uses cytochromes encoded by other genes. Higher plants contain multiple Cb5 genes, and it has been shown that certain Cb5 genes of Arabidopsis thaliana facilitate the accumulation of more desaturation products than others when co-expressed with FAD2 [Kumar12].

The FAD2 gene was identified using T-DNA insertions [Okuley94]. The gene was cloned and expressed in fad2 mutant plants and shown to complement the mutant fatty acid phenotype [Okuley94].

When grown at 22°C, FAD2 mutants of Arabidopsis thaliana are similar in growth and appearance to the wild type. However, they show a dramatic chilling-sensitive phenotype when transferred to 6°C, demonstrating that polyunsaturated membranes are essential for maintaining cellular function and plant viability at low temperatures [Miquel93].

The ER desaturases FAD2 (18:1) and FAD3 (18:2) have been shown to act on fatty acids at both the sn-1 and sn-2 positions of phosphatidylcholine [Miquel92, Browse93]. It is possible that they act on other phospholipids as well, although this hasn't been verified [Ohlrogge95].

Citations: [Covello96]

Locations: endoplasmic reticulum

Molecular Weight of Polypeptide: 44.048 kD (from nucleotide sequence)

Unification Links: ArrayExpress:P46313 , PhylomeDB:P46313 , Pride:P46313 , String:3702.AT3G12120.2-P , TAIR:AT3G12120 , UniProt:P46313

Relationship Links: Entrez-Nucleotide:PART-OF:L26296 , InterPro:IN-FAMILY:IPR005804 , InterPro:IN-FAMILY:IPR021863 , Pfam:IN-FAMILY:PF00487 , Pfam:IN-FAMILY:PF11960

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

GO Terms:

Cellular Component: GO:0005783 - endoplasmic reticulum


Enzymatic reaction of: oleoyl-lipid 12-desaturase (acyl-lipid ω-6 desaturase)

EC Number: 1.14.19.f

a [glycerolipid]-oleate + 2 a ferrocytochrome b5 + oxygen + 2 H+ <=> a [glycerolipid]-linoleate + 2 a ferricytochrome b5 + 2 H2O

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

In Pathways: linoleate biosynthesis I (plants)


Enzymatic reaction of: 1-16:0-2-18:1-phosphatidylcholine 2-12-desaturase (acyl-lipid ω-6 desaturase)

EC Number: 1.14.19.f

1-16:0-2-18:1-phosphatidylcholine + 2 a ferrocytochrome b5 + oxygen + 2 H+ <=> 1-palmitoyl-2-linoleoyl-phosphatidylcholine + 2 a ferricytochrome b5 + 2 H2O

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

In Pathways: phospholipid desaturation


Enzymatic reaction of: 1-18:1-2-18:2-phosphatidylcholine 1-12-desaturase (acyl-lipid ω-6 desaturase)

EC Number: 1.14.19.f

1-18:1-2-18:2-phosphatidylcholine + 2 a ferrocytochrome b5 + oxygen + 2 H+ <=> 1-18:2-2-18:2-sn-glycerol-3-phosphocholine + 2 a ferricytochrome b5 + 2 H2O

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

In Pathways: phospholipid desaturation


Enzymatic reaction of: 1-18:2-2-18:1-phosphatidylcholine 2-12-desaturase (acyl-lipid ω-6 desaturase)

EC Number: 1.14.19.f

1-18:2-2-18:1-phosphatidylcholine + 2 a ferrocytochrome b5 + oxygen + 2 H+ <=> 1-18:2-2-18:2-sn-glycerol-3-phosphocholine + 2 a ferricytochrome b5 + 2 H2O

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

In Pathways: phospholipid desaturation


Enzymatic reaction of: 1-18:1-2-18:3-phosphatidylcholine 1-12-desaturase (acyl-lipid ω-6 desaturase)

EC Number: 1.14.19.f

1-18:1-2-18:3-phosphatidylcholine + 2 a ferrocytochrome b5 + oxygen + 2 H+ <=> 1-18:2-2-18:3-phosphatidylcholine + 2 a ferricytochrome b5 + 2 H2O

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

In Pathways: phospholipid desaturation


Enzymatic reaction of: 1-18:3-2-18:1-phosphatidylcholine 2-12-desaturase (acyl-lipid ω-6 desaturase)

EC Number: 1.14.19.f

1-18:3-2-18:1-phosphatidylcholine + 2 a ferrocytochrome b5 + oxygen + 2 H+ <=> 1-18:3-2-18:2-phosphatidylcholine + 2 a ferricytochrome b5 + 2 H2O

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

In Pathways: phospholipid desaturation


Enzymatic reaction of: 1-18:1-2-18:1-phosphatidylcholine 2-12-desaturase (acyl-lipid ω-6 desaturase)

EC Number: 1.14.19.f

1-18:1-2-18:1-sn-glycerol-3-phosphocholine + 2 a ferrocytochrome b5 + oxygen + 2 H+ <=> 1-18:1-2-18:2-phosphatidylcholine + 2 a ferricytochrome b5 + 2 H2O

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

In Pathways: phospholipid desaturation


Enzymatic reaction of: 1-18:1-2-18:1-sn-glycerol-3-phosphocholine 1-12-desaturase (acyl-lipid ω-6 desaturase)

EC Number: 1.14.19.f

1-18:1-2-18:1-sn-glycerol-3-phosphocholine + 2 a ferrocytochrome b5 + oxygen + 2 H+ <=> 1-18:2-2-18:1-phosphatidylcholine + 2 a ferricytochrome b5 + 2 H2O

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

In Pathways: phospholipid desaturation


References

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

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

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

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


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
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