A fatty acid desaturase is an enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 that removes two hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 atoms from a fatty acid

Fatty acid

In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

, creating a carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

/carbon double bond

Covalent bond

A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....

. These desaturases are classified as

• delta - indicating that the double bond is created at a fixed position from the carboxyl group of a fatty acid
  Fatty acid
  In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
  
   (for example, Δ⁹desaturase
  Stearoyl-CoA desaturase-1
  Stearoyl-CoA desaturase is a protein that in humans is encoded by the SCD gene.Stearoyl-CoA desaturase-1is a key enzyme in fatty acid metabolism. It is responsible for forming a double bond in Stearoyl-CoA...
  
   creates a double bond at the 9th position from the carboxyl end).
• omega (e.g. ω³desaturase) - indicating the double bond is created between the third and fourth carbon from the methyl end of the fatty acid.

In the biosynthesis

Fatty acid synthesis

Fatty acid synthesis is the creation of fatty acids from acetyl-CoA and malonyl-CoA precursors through action of enzymes called fatty acid synthases...

 of essential fatty acid

Essential fatty acid

Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them...

s, an elongase alternates with different desaturases (for example, Δ⁶desaturase) repeatedly inserting an ethyl group

Ethyl group

In chemistry, an ethyl group is an alkyl substituent derived from ethane . It has the formula -C2H5 and is very often abbreviated -Et.Ethylation is the formation of a compound by introduction of the ethyl functional group, C2H5....

, then forming a double bond.

Role in human metabolism

Four desaturases occur in humans: Δ⁹desaturase, Δ⁶desaturase, Δ⁵ desaturase, and Δ⁴ desaturase.

Δ⁹desaturase, also known as Stearoyl-CoA desaturase-1

Stearoyl-CoA desaturase-1

Stearoyl-CoA desaturase is a protein that in humans is encoded by the SCD gene.Stearoyl-CoA desaturase-1is a key enzyme in fatty acid metabolism. It is responsible for forming a double bond in Stearoyl-CoA...

, is used to synthesize oleic acid

Oleic acid

Oleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable fats. It has the formula CH37CH=CH7COOH. It is an odorless, colourless oil, although commercial samples may be yellowish. The trans isomer of oleic acid is called elaidic acid...

, a monounsaturated, ubiquitous component of all cells in the human body. Δ⁹desaturase produces oleic acid by desaturating stearic acid

Stearic acid

Stearic acid is the saturated fatty acid with an 18 carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is CH316CO2H. Its name comes from the Greek word στέαρ "stéatos", which means tallow. The salts and esters of stearic acid are called stearates...

, a saturated fatty acid either synthesized in the body from palmitic acid

Palmitic acid

Palmitic acid, or hexadecanoic acid in IUPAC nomenclature, is one of the most common saturated fatty acids found in animals and plants. Its molecular formula is CH314CO2H. As its name indicates, it is a major component of the oil from palm trees . Palmitate is a term for the salts and esters of...

 or ingested directly.

Δ⁶ and Δ⁵ desaturases are required for the synthesis of highly unsaturated fatty acids such as eicosopentaenoic

Eicosapentaenoic acid

Eicosapentaenoic acid is an omega-3 fatty acid. In physiological literature, it is given the name 20:5. It also has the trivial name timnodonic acid...

 and docosahexaenoic acid

Docosahexaenoic acid

Docosahexaenoic acid is an omega-3 fatty acid that is a primary structural component of the human brain and retina. In chemical structure, DHA is a carboxylic acid with a 22-carbon chain and six cis double bonds; the first double bond is located at the third carbon from the omega end...

s (synthesized from a-linolenic acid), and arachidonic acid

Arachidonic acid

Arachidonic acid is a polyunsaturated omega-6 fatty acid 20:4.It is the counterpart to the saturated arachidic acid found in peanut oil, Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6).It is the counterpart to the saturated arachidic acid found in peanut oil,...

 (synthesized from linoleic acid

Linoleic acid

Linoleic acid is an unsaturated n-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2...

). 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.

• Human fatty acid desaturases:

DEGS1; DEGS2; FADS1

FADS1

Fatty acid desaturase 1 is an enzyme that in humans is encoded by the FADS1 gene.- Function :The protein encoded by this gene is a member of the fatty acid desaturase gene family. Desaturase enzymes regulate unsaturation of fatty acids through the introduction of double bonds between defined...

; FADS2

FADS2

Fatty acid desaturase 2 also known as delta fatty acid desaturase is an enzyme that in humans is encoded by the FADS2 gene.- Function :Fatty acid desaturase 2 is a member of the fatty acid desaturase gene family...

; FADS3; FADS6; SCD4; SCD5;

Classification

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

Family 1 includes Stearoyl-CoA desaturase-1

Stearoyl-CoA desaturase-1

Stearoyl-CoA desaturase is a protein that in humans is encoded by the SCD gene.Stearoyl-CoA desaturase-1is a key enzyme in fatty acid metabolism. It is responsible for forming a double bond in Stearoyl-CoA...

(SCD) .

Family 2 is composed of:

• - Bacterial fatty acid desaturases.
• - Plant stearoyl-acyl-carrier-protein desaturase , this enzyme 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 membranes glycerolipids. DesA 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.