enzymology 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. ...

, a linoleoyl-CoA desaturase (also Delta 6 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 converts between types of fatty acids, which are essential nutrients in the human body. The

mainly catalyzes the

chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breakin ...

:linoleoyl-CoA + AH₂ + O₂

\rightleftharpoons

gamma-linolenoyl-CoA + A + 2 H₂O The 3 substrates of this enzyme are linoleoyl-CoA, an

electron acceptor An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process. Electron acceptors are sometimes mista ...

AH₂, and O₂, whereas its 3

products Product may refer to: Business * Product (business), an item that serves as a solution to a specific consumer problem. * Product (project management), a deliverable or set of deliverables that contribute to a business solution Mathematics * Prod ...

are gamma-linolenoyl-CoA, the reduction product A, and H₂O. This enzyme belongs to the family of

oxidoreductase In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another, the oxidant, also called the electron acceptor. This group of enzymes usually ut ...

s, specifically those acting on paired donors, with O2 as oxidant and incorporation or reduction of oxygen. The oxygen incorporated need not be derived from O2 with oxidation of a pair of donors resulting in the reduction of O to two molecules of water. The

systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature. A semisystematic name or semitrivial ...

of this enzyme class is linoleoyl-CoA,hydrogen-donor:oxygen oxidoreductase. Other names in common use include Delta6-desaturase (D6D or Δ-6-desaturase), Delta6-fatty acyl-CoA desaturase, Delta6-acyl CoA desaturase, fatty acid Delta6-desaturase, fatty acid 6-desaturase, linoleate desaturase, linoleic desaturase, linoleic acid desaturase, linoleoyl CoA desaturase, linoleoyl-coenzyme A desaturase, and long-chain fatty acid Delta6-desaturase. This enzyme participates in linoleic acid metabolism. It employs one cofactor,

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in fro ...

. The enzyme is molecularly identical across all living things (preserved across

Kingdom (biology) In biology, a kingdom is the second highest taxonomic rank, just below domain. Kingdoms are divided into smaller groups called phyla. Traditionally, some textbooks from the United States and Canada used a system of six kingdoms (Animalia, P ...

) it is present in animals, plants, and

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blue ...

. D6D is one of the 3

fatty acid desaturase 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 ...

s present in humans along with Δ-5 and Δ-9, named so because it was thought to desaturate bond between carbons 6 and 7, counting from

carboxyl group In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxyli ...

(with the carboxyl group carbon numbered one). The number 6 in the name of the enzyme has nothing to do with

omega-6 fatty acids Omega-6 fatty acids (also referred to as ω-6 fatty acids or ''n''-6 fatty acids) are a family of polyunsaturated fatty acids that have in common a final carbon-carbon double bond in the ''n''-6 position, that is, the sixth bond, counting from ...

. In humans, it is encoded by the

FADS2 Fatty acid desaturase 2 (FADS2) is encoded by the ''FADS2'' gene, the associated enzyme is sometimes known as FADS2 as well. Its main associated enzyme is Delta 6 desaturase (D6D) however the human enzyme been shown to also catalyze some delta-8 ...

gene.

Molecular activity

D6D is a desaturase enzyme, i.e. introduces a double bond in a specific position of long-chain fatty acids. Among them, it converts between various forms of Omega-3 and Omega-6 fatty acids: * primarily (in humans): ** cis-

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. ...

to gamma-linolenic acid (GLA) **

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 L ...

to Sapienic acid * less efficiently in humans: ** ALA to Stearidonic acid, along with an elongase to provide EPA. ** Tetracosatetranoic acid to tetracosapentanoic acid, an intermediate step between EPA to DHA synthesis. D6D is obligatory along with various elongases to convert to longer chain omega-3's, such as between ALA to EPA as well as EPA to DHA. GLA deficiencies in animals including humans have shown wide effects down the line -- Dihomogamma-linolenic acid (DGLA) and

Prostaglandin E1 Prostaglandin E1 (PGE1), also known as alprostadil, is a naturally occurring prostaglandin which is used as a medication. In infants with congenital heart defects, it is delivered by slow injection into a vein to open the ductus arteriosus unti ...

deficiency. PGE1 activates T lymphocytes, inhibits smooth muscle proliferation and thrombosis, is important in gonadal function and raises

cyclic AMP Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger important in many biological processes. cAMP is a derivative of adenosine triphosphate (ATP) and used for intracellular signal transd ...

levels in many tissues. It also affects viability of

sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum ...

. and

dermatitis Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can ...

Variability

6D is a long chain PUFA rate limiter, has greater affinity for ALA than for linoleic acid, nevertheless many diets have far more linoleic acid present, resulting in reduced levels of

alpha-Linolenic acid ''alpha''-Linolenic acid (ALA), also known as α-Linolenic acid (from Greek ''alpha'' meaning "first" and ''linon'' meaning flax), is an ''n''−3, or omega-3, essential fatty acid. ALA is found in many seeds and oils, including flaxseed, wal ...

EPA The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it b ...

conversion. Women tend to have higher levels of D6D due to the effects of

estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal ac ...

Inhibiting factors

* alcohol, radiation, diabetes

Agonists

* Moderate food restriction (up to 300%) * Low levels of Omega-3's.

Technical reading

* EctoGEM
1.14.19.3-RXN

''Toxoplasma gondii''

Felines lack D6D activity in their guts and accumulate systemic linoleic acid. This increase in linoleic acid in cats has an influence in causing the sexual cycle of ''T. gondii'' to be restricted to felines, with linoleic acid stimulating ''T. gondii'' sexual reproduction.

References

* EC 1.14.19 Iron enzymes Enzymes of unknown structure {{1.14-enzyme-stub