Fatty acid desaturase

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Fatty acid desaturase, type 1
OPM superfamily431
OPM protein4zyo
Available protein structures:
Pfam  structures / ECOD  
PDBsumstructure summary
Fatty acid desaturase, type 2
Available protein structures:
Pfam  structures / ECOD  
PDBsumstructure summary

A fatty acid desaturase is an enzyme that removes two hydrogen atoms from a fatty acid, creating a carbon/carbon double bond. These desaturases are classified as:

  • Delta - indicating that the double bond is created at a fixed position from the carboxyl end of a fatty acid chain. For example, Δ9 desaturase creates a double bond between the ninth and tenth carbon atom from the carboxyl end.
  • Omega - indicating the double bond is created at a fixed position from the methyl end of a fatty acid chain. For instance, ω3 desaturase creates a double bond between the third and fourth carbon atom from the methyl end. In other words, it creates an omega-3 fatty acid.

For example, Δ6 desaturation introduces a double bond between carbons 6 and 7 of Linoleic acid (LA C18H32O2; 18:2-n6) and α-Linolenic acid (ALA: C18H30O2; 18:3-n3), creating γ-linolenic acid (GLA: C18H30O2,18:3-n6) and stearidonic acid (SDA: C18H28O2; 18:4-n3) respectively.[1]

In humans, Δ17-desaturase is able to turn omega 6 into omega 3 essential fatty acids.

In the biosynthesis of essential fatty acids, an elongase alternates with different desaturases (for example, Δ6desaturase) repeatedly inserting an ethyl group, then forming a double bond.


Maintain structure and function of membranes within cells of the organisms above, by its esterification of highly unsaturated fatty acids (HUFAs) into phospholipids, and cell signaling.[2] This is important when temperatures changes and the membrane is under distress. The enzyme creates the double bond C-Cs which allow the membrane to become more fluid and the temperature is decreased.[3] When temperatures change, a phase transition occurs. In the case of a temperature decrease, the membrane gels and becomes solid which can result in cracks and the imbedded proteins cannot partake in conformational changes, therefore it is important to maintain membrane fluidity.[4]

Role in human metabolism[edit]

Fatty acid desaturase appear in all organisms: for example, bacteria, fungus, plants, animals and humans.[3] Four desaturases occur in humans: Δ9 desaturase, Δ6 desaturase, Δ5 desaturase, and Δ4 desaturase.[5]

Δ9 desaturase, also known as stearoyl-CoA desaturase-1, is used to synthesize oleic acid, a monounsaturated, ubiquitous component of all cells in the human body, and the major fatty acid in mammalian adipose triglycerides, and also used for phospholipid and cholesteryl ester synthesis.[2] Δ9 desaturase produces oleic acid (C18H34O2; 18:1-n9) by desaturating stearic acid (SA: C18H36O2; 18:0), a saturated fatty acid either synthesized in the body from palmitic acid (PA: C16H32O2; 16:0) or ingested directly.

Δ6 and Δ5 desaturases are required for the synthesis of highly unsaturated fatty acids such as eicosopentaenoic and docosahexaenoic acids (synthesized from α-linolenic acid); arachidonic acid and adrenic acid (synthesized from linoleic acid). This is a multi-stage process requiring successive actions by elongase and desaturase enzymes. The genes coding for Δ6 and Δ5 desaturase production have been located on human chromosome 11.[6]

Synthesis of LC-PUFAs in humans and many other eukaryotes starts with:

* Linoleic acid (LA: C18H32O2; 18:2-n6) → Δ6-desaturation → γ-linolenic acid (GLA: C18H30O2; 18:3-n6) → Δ6-specific elongase (introducing two carbons) → Dihomo-gamma-linolenic acid DGLA: C20H34O2; 20:3-n6) → Δ5-desaturase → arachidonic acid (AA: C20H32O2; 20:4-n6) → also endocannabinoids.

* α-Linolenic acid (ALA: C18H30O2; 18:3-n3) → Δ6-desaturation → stearidonic acid (SDA: C18H28O2; 18:4-n3) and/or → Δ6-specific elongase → eicosatetraenoic acid (ETA: C20H32O2; 20:4-n3) → Δ5-desaturase → eicosapentaenoic acid (EPA: C20H30O2; 20:5-n3).

By a Δ17-desaturase, gamma-Linolenic acid (GLA: C18H30O2; 18:3-n6) can be further converted to Stearidonic acid (SDA: C18H28O2; 18:4-n3), dihomo-gamma-linolenic acid (DHGLA/DGLA: C20H34O2; 20:3-n6) to eicosatetraenoic acid (ETA: C20H32O2; 20:4-n3; omega-3 Arachidonic acid)[7] and arachidonic acid (AA: C20H32O2; 20:4-n6) to eicosapentaenoic acid (EPA: C20H30O2; 20:5-n3), respectively.[1]

* Anandamide (AEA: C22H37NO2; 20:4,n-6) is an N-acylethanolamine resulting from the formal condensation of the carboxy group of arachidonic acid (AA: C20H32O2; 20:4-n6) with the amino group of ethanolamine (C2H7NO), bind preferably to CB1 receptors.[9]

* 2-arachidonoylglycerol (2-AG: C23H38O4; 20:4-n6) is an endogenous agonist of the cannabinoid receptors (CB1 and CB2), and the physiological ligand for the cannabinoid CB2 receptor.[10] It is an ester formed from omega-6-arachidonic acid (AA: C20H32O2; 20:4-n6) and glycerol (C3H8O3).[11]

Vertebrates are unable to synthesize polyunsaturated fatty acids because they do not have the necessary fatty acid desaturases to "convert oleic acid (18:1n-9) into linoleic acid (18:2n-6) and α-linolenic acid (18:3n-3)".[6] Linoleic acid (LA) and α-linolenic acid (ALA) are essential for human health and development, and should therefore be consumed by diets, like 15 ml of hemp seed oil, or/and 33 gram of hemp seed protein a day,[12] can provide all the protein, essential fatty acids, and dietary fiber necessary for human survival for one day,[13] as their absence has been found responsible for the development of a wide range of diseases such as metabolic disorders,[14] cardiovascular disorders, inflammatory processes, viral infections, certain types of cancer and autoimmune disorders.[15]

Human fatty acid desaturases include: DEGS1; DEGS2; FADS1; FADS2; FADS3; FADS6; SCD4; SCD5


Δ-desaturases are represented by two distinct families which do not seem to be evolutionarily related.

Family 1 includes Stearoyl-CoA desaturase-1 (SCD) (EC[16]

Family 2 is composed of:

  • Bacterial fatty acid desaturases.
  • Plant stearoyl-acyl-carrier-protein desaturase (EC,[17] an enzyme that catalyzes the introduction of a double bond at the delta-9 position of steraoyl-ACP to produce oleoyl-ACP. This enzyme is responsible for the conversion of saturated fatty acids to unsaturated fatty acids in the synthesis of vegetable oils.
  • Cyanobacterial DesA,[18] an enzyme that can introduce a second cis double bond at the delta-12 position of fatty acid bound to membrane glycerolipids. This enzyme is involved in chilling tolerance; the phase transition temperature of lipids of cellular membranes being dependent on the degree of unsaturation of fatty acids of the membrane lipids.

Acyl-CoA dehydrogenases[edit]

Acyl-CoA dehydrogenases are enzymes that catalyze formation of a double bond between C2 (α) and C3 (β) of the acyl-CoA thioester substrates.[19] Flavin adenine dinucleotide (FAD) is a required co-factor.


See also[edit]

N-acylethanolamine (NAE)


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This article incorporates text from the public domain Pfam and InterPro: IPR005067