A fatty acid desaturase is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

that removes two

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

atoms from a

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, f ...

, creating a

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...

/carbon

double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betwee ...

. These desaturases are classified as: * Delta - indicating that the double bond is created at a fixed position from the carboxyl end of a

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 In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in ...

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 Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond, three atoms away from the terminal methyl group in their chem ...

. For example, Δ6 desaturation introduces a double bond between carbons 6 and 7 of

Linoleic acid Linoleic acid (LA) is an organic compound with the formula COOH(CH2)7CH=CHCH2CH=CH(CH2)4CH3. Both alkene groups are ''cis''. It is a fatty acid sometimes denoted 18:2 (n-6) or 18:2 ''cis''-9,12. A linoleate is a salt or ester of this 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. In humans, Δ17- desaturase is able to turn omega 6 into omega 3 essential fatty acids. In the

biosynthesis Biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecul ...

of essential fatty acids, an elongase alternates with different desaturases (for example, Δ⁶desaturase) repeatedly inserting an

ethyl group In organic chemistry, an ethyl group (abbr. Et) is an alkyl substituent with the formula , derived from ethane (). ''Ethyl'' is used in the International Union of Pure and Applied Chemistry's nomenclature of organic chemistry for a saturated ...

, then forming a double bond.

Function

Maintain structure and function of

membranes A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Bi ...

within cells of the organisms above, by its

esterification In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...

of highly

unsaturated fatty acids In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food. The term often refers specifically to triglycerides (triple est ...

( HUFAs) into

phospholipids Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids ...

, and

cell signaling In biology, cell signaling (cell signalling in British English) or cell communication is the ability of a cell to receive, process, and transmit signals with its environment and with itself. Cell signaling is a fundamental property of all cellula ...

. 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. 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.

Role in human metabolism

Fatty acid desaturase appear in all organisms: for example, bacteria, fungus, plants, animals and humans. Four desaturases occur in humans: Δ⁹ desaturase, Δ⁶ desaturase, Δ⁵ desaturase, and Δ⁴ desaturase. Δ⁹ desaturase, also known as stearoyl-CoA desaturase-1, is used to synthesize

oleic acid Oleic acid is a fatty acid that occurs naturally in various animal and vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish. In chemical terms, oleic acid is classified as a monounsaturated o ...

, a monounsaturated, ubiquitous component of all cells in the human body, and the major fatty acid in

mammalian Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...

adipose triglycerides, and also used for

phospholipid Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...

and

cholesteryl ester 300px, Cholesterol oleate, a member of the cholesteryl ester family Cholesteryl ester, a dietary lipid, is an ester of cholesterol. The ester bond is formed between the carboxylate group of a fatty acid and the hydroxyl group of cholesterol. Chol ...

synthesis. Δ⁹ desaturase produces oleic acid (C₁₈H₃₄O₂; 18:1-n9) by desaturating

stearic acid Stearic acid ( , ) is a saturated fatty acid with an 18-carbon chain. The IUPAC name is octadecanoic acid. It is a waxy solid and its chemical formula is C17H35CO2H. Its name comes from the Greek word στέαρ "''stéar''", which means ta ...

(SA: C₁₈H₃₆O₂; 18:0), a saturated fatty acid either synthesized in the body from

palmitic acid Palmitic acid (hexadecanoic acid in IUPAC nomenclature) is a fatty acid with a 16-carbon chain. It is the most common saturated fatty acid found in animals, plants and microorganisms.Gunstone, F. D., John L. Harwood, and Albert J. Dijkstra. The ...

(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 acid Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is a primary structural component of the human brain, cerebral cortex, skin, and retina. In physiological literature, it is given the name 22:6(n-3). It can be synthesized from alpha-lin ...

s (synthesized from α-linolenic acid);

arachidonic acid Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6), or 20:4(5,8,11,14). It is structurally related to the saturated arachidic acid found in cupuaçu butter. Its name derives from the New Latin word ''ara ...

and adrenic acid (synthesized from

linoleic acid Linoleic acid (LA) is an organic compound with the formula COOH(CH2)7CH=CHCH2CH=CH(CH2)4CH3. Both alkene groups are ''cis''. It is a fatty acid sometimes denoted 18:2 (n-6) or 18:2 ''cis''-9,12. A linoleate is a salt or ester of this 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.

Synthesis Synthesis or synthesize may refer to: Science Chemistry and biochemistry * Chemical synthesis, the execution of chemical reactions to form a more complex molecule from chemical precursors **Organic synthesis, the chemical synthesis of organ ...

of LC-PUFAs in

humans" \n\n\n\n\nThe robots exclusion standard, also known as the robots exclusion protocol or simply robots.txt, is a standard used by websites to indicate to visiting web crawlers and other web robots which portions of the site they are allowed to visi ...

and many other

eukaryotes Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacter ...

starts with: *

(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 →

(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) and

(AA: C₂₀H₃₂O₂; 20:4-n6) to eicosapentaenoic acid (EPA: C₂₀H₃₀O₂; 20:5-n3), respectively. *

Fatty acids In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an B ...

with at least 20 carbons (C₂₀) and three double bonds (20:3) bind to CB1 receptors. *

Arachidonic acid Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6), or 20:4(5,8,11,14). It is structurally related to the saturated arachidic acid found in cupuaçu butter. Its name derives from the New Latin word ''ara ...

(AA) is also the catalyst to the formation of the two main endocannabinoids,

Anandamide Anandamide (ANA), also known as ''N''-arachidonoylethanolamine (AEA), is a fatty acid neurotransmitter. Anandamide was the first endocannabinoid to be discovered: it participates in the body's endocannabinoid system by binding to cannabinoid r ...

(AEA) and 2-arachidonoylglycerol (2-AG). *

(AEA: C₂₂H₃₇ NO₂; 20:4,n-6) is an ''N''-acylethanolamine resulting from the formal

condensation Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapo ...

of the carboxy group of arachidonic acid (AA: C₂₀H₃₂O₂; 20:4-n6) with the amino group of ethanolamine (C₂H₇ NO), bind preferably to CB1 receptors. * 2-arachidonoylglycerol (2-AG: C₂₃H₃₈O₄; 20:4-n6) is an endogenous

agonist An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the ag ...

of the cannabinoid receptors (CB1 and CB2), and the physiological

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elect ...

for the cannabinoid

CB2 receptor The cannabinoid receptor type 2, abbreviated as CB2, is a G protein-coupled receptor from the cannabinoid receptor family that in humans is encoded by the ''CNR2'' gene. It is closely related to the cannabinoid receptor type 1 (CB1), which is l ...

. It is an

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...

formed from omega-6-arachidonic acid (AA: C₂₀H₃₂O₂; 20:4-n6) and

glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...

(C₃H₈O₃). Vertebrates are unable to synthesize polyunsaturated fatty acids because they do not have the necessary fatty acid desaturases to "convert oleic acid (18:1''n''-9) into linoleic acid (18:2''n''-6) and α-linolenic acid (18:3''n''-3)". 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, can provide all the

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

, essential fatty acids, and

dietary fiber Dietary fiber (in British English fibre) or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes. Dietary fibers are diverse in chemical composition, and can be grouped generally by t ...

necessary for human survival for one day, as their absence has been found responsible for the development of a wide range of diseases such as

metabolic disorder A metabolic disorder is a disorder that negatively alters the body's processing and distribution of macronutrients, such as proteins, fats, and carbohydrates. Metabolic disorders can happen when abnormal chemical reactions in the body alter t ...

cardiovascular disorders Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, hea ...

, inflammatory processes, viral infections, certain types of

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

and autoimmune disorders. Human fatty acid desaturases include: DEGS1; DEGS2; FADS1; FADS2; FADS3; FADS6; SCD4; SCD5

Classification

Δ-desaturases are represented by two distinct families which do not seem to be evolutionarily related. Family 1 includes Stearoyl-CoA desaturase-1 (SCD) (). Family 2 is composed of: * Bacterial fatty acid desaturases. * Plant stearoyl- acyl-carrier-protein desaturase (), 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, 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

Acyl-CoA dehydrogenases are

enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. ...

that catalyze formation of a double bond between C2 (α) and C3 (β) of the acyl-CoA thioester substrates.

Flavin adenine dinucleotide Flavin may refer to: Placename * Flavin, Aveyron, a commune in southern France Surname * Adrian Flavin (born 1979), a professional rugby player * Christopher Flavin, president of the Worldwatch Institute * Dan Flavin (1933–1996), a minimalis ...

(FAD) is a required co-factor.

References

{{InterPro content, IPR005067 Enzymes

Function

Role in human metabolism

Classification

Acyl-CoA dehydrogenases

See also

References