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Phosphatidylcholines (PC) are a class of
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 ...
s that incorporate
choline Choline is an essential nutrient for humans and many other animals. Choline occurs as a cation that forms various salts (X− in the depicted formula is an undefined counteranion). Humans are capable of some ''de novo synthesis'' of choline but ...
as a headgroup. They are a major component of
biological membrane A biological membrane, biomembrane or cell membrane is a selectively permeable membrane that separates the interior of a cell from the external environment or creates intracellular compartments by serving as a boundary between one part of the ...
s and can be easily obtained from a variety of readily available sources, such as
egg yolk Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example be ...
or soybeans, from which they are mechanically or chemically extracted using
hexane Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14. It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relatively ...
. They are also a member of the
lecithin Lecithin (, from the Greek ''lekithos'' "yolk") is a generic term to designate any group of yellow-brownish fatty substances occurring in animal and plant tissues which are amphiphilic – they attract both water and fatty substances (and so ar ...
group of yellow-brownish fatty substances occurring in animal and plant tissues. Dipalmitoyl phosphatidylcholine (a.k.a. lecithin) is a major component of
pulmonary surfactant Pulmonary surfactant is a surface-active complex of phospholipids and proteins formed by type II alveolar cells. The proteins and lipids that make up the surfactant have both hydrophilic and hydrophobic regions. By adsorbing to the air-water inte ...
and is often used in the L/S ratio to calculate fetal lung maturity. While phosphatidylcholines are found in all plant and animal cells, they are absent in the membranes of most bacteria, including ''
Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...
''. Purified phosphatidylcholine is produced commercially. The name ''lecithin'' was derived from
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
λέκιθος, ''lekithos'' 'egg yolk' by
Theodore Nicolas Gobley TheodoreSome earlier Wikipedia versions, e.g. wiki.de, write Nicolas-Theodore; family sources (see wiki.fr article discussion) guarantee Theodore as ordinary given name, plus a publication in March 1848, "Recherches sur la présence de l'arsenic d ...
, a French chemist and pharmacist of the mid-19th century, who applied it to the egg yolk phosphatidylcholine that he identified in 1847. Gobley eventually completely described his lecithin from chemical structural point of view, in 1874. Phosphatidylcholines are such a major component of lecithin that in some contexts the terms are sometimes used as synonyms. However, lecithin extracts consist of a mixture of phosphatidylcholine and other compounds. It is also used along with
sodium taurocholate Taurocholic acid, known also as cholaic acid, cholyltaurine, or acidum cholatauricum, is a deliquescent yellowish crystalline bile acid involved in the emulsification of fats. It occurs as a sodium salt in the bile of mammals. It is a conjugate ...
for simulating fed- and fasted-state biorelevant media in dissolution studies of highly
lipophilic Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipoph ...
drugs. Phosphatidylcholine is a major constituent of cell membranes and pulmonary surfactant, and is more commonly found in the exoplasmic or outer leaflet of a
cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...
. It is thought to be transported between membranes within the cell by phosphatidylcholine transfer protein (PCTP). Phosphatidylcholine also plays a role in membrane-mediated
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 ...
and PCTP activation of other enzymes.


Structure and physical properties

This phospholipid is composed of a choline head group and glycerophosphoric acid, with a variety of fatty acids. Usually, one is a saturated fatty acid (in the given figure, this is
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 ...
(hexadecanoic acid, H3C-(CH2)14-COOH); margaric acid (heptadecanoic acid, H3C-(CH2)15-COOH), identified by Gobley in egg yolk, also belong to that class); and the other is an
unsaturated 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, fr ...
(here oleic acid, or 9Z-octadecenoic acid, as in Gobley's original egg yolk lecithin). However, there are also examples of disaturated species. Animal lung phosphatidylcholine, for example, contains a high proportion of
dipalmitoylphosphatidylcholine Dipalmitoylphosphatidylcholine (DPPC) is a phospholipid (and a lecithin) consisting of two C16 palmitic acid groups attached to a phosphatidylcholine head-group. It is the main constituent of pulmonary surfactants, which reduces the work of breat ...
.
Phospholipase D Phospholipase D (EC 3.1.4.4, lipophosphodiesterase II, lecithinase D, choline phosphatase, PLD; systematic name phosphatidylcholine phosphatidohydrolase) is an enzyme of the phospholipase superfamily that catalyses the following reaction : a p ...
catalyzes the hydrolysis of phosphatidylcholine to form
phosphatidic acid Phosphatidic acids are anionic phospholipids important to cell signaling and direct activation of lipid-gated ion channels. Hydrolysis of phosphatidic acid gives rise to one molecule each of glycerol and phosphoric acid and two molecules of fatty a ...
(PA), releasing the soluble
choline Choline is an essential nutrient for humans and many other animals. Choline occurs as a cation that forms various salts (X− in the depicted formula is an undefined counteranion). Humans are capable of some ''de novo synthesis'' of choline but ...
headgroup into the
cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochond ...
.


Possible health benefits


Senescence

A 2009
systematic review A systematic review is a scholarly synthesis of the evidence on a clearly presented topic using critical methods to identify, define and assess research on the topic. A systematic review extracts and interprets data from published studies on t ...
of
clinical trials Clinical trials are prospective biomedical or behavioral research studies on human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel vaccines, drugs, dietar ...
in humans found that there was not enough evidence to support supplementation of lecithin or phosphatidylcholine in dementia. The study found that a moderate benefit could not be ruled out until further large scale studies were performed.


Lipolysis

Though phosphatidylcholine has been studied as an alternative to liposuction, there are no peer-reviewed studies that have shown it to have comparable effects. Injection of phosphatidylcholine in lipomas has been studied, though results have been mixed.


Ulcerative colitis

Treatment of ulcerative colitis with oral intake of phosphatidylcholine has been shown to result in decreased disease activity.


Possible health risks

A 2011 report linked the microbial catabolites of phosphatidylcholine with increased
atherosclerosis Atherosclerosis is a pattern of the disease arteriosclerosis in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. At onset there are usually no ...
in mice through the production of
choline Choline is an essential nutrient for humans and many other animals. Choline occurs as a cation that forms various salts (X− in the depicted formula is an undefined counteranion). Humans are capable of some ''de novo synthesis'' of choline but ...
, trimethylamine oxide, and
betaine A betaine () in chemistry is any neutral chemical compound with a positively charged cationic functional group, such as a quaternary ammonium or phosphonium cation (generally: onium ions) that bears no hydrogen atom and with a negatively charged ...
.


Biosynthesis

Although multiple pathways exist for the biosynthesis of phosphatidylcholine, the predominant route in
eukaryote 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. Bact ...
s involves condensation between
diacylglycerol A diglyceride, or diacylglycerol (DAG), is a glyceride consisting of two fatty acid chains covalently bonded to a glycerol molecule through ester linkages. Two possible forms exist, 1,2-diacylglycerols and 1,3-diacylglycerols. DAGs can act as s ...
(DAG) and cytidine 5'-diphosphocholine (CDP-choline or citicoline). The conversion is mediated by the enzyme diacylglycerol cholinephosphotransferase. Another pathway, mainly operative in the
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...
involves
methylation In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These t ...
of
phosphatidylethanolamine Phosphatidylethanolamine (PE) is a class of phospholipids found in biological membranes. They are synthesized by the addition of cytidine diphosphate-ethanolamine to diglycerides, releasing cytidine monophosphate. ''S''-Adenosyl methionine can ...
with ''S''-adenosyl methionine (SAM) being the methyl group donor.


See also

* CDP choline *
Lysophosphatidylcholine Lysophosphatidylcholines (LPC, lysoPC), also called lysolecithins, are a class of chemical compounds which are derived from phosphatidylcholines. Overview Lysophosphatidylcholines are produced within cells mainly by the enzyme phospholipase ...
*
Phosphatidylserine Phosphatidylserine (abbreviated Ptd-L-Ser or PS) is a phospholipid and is a component of the cell membrane. It plays a key role in cell cycle signaling, specifically in relation to apoptosis. It is a key pathway for viruses to enter cells via ap ...
* Saturated fatty acid *
Unsaturated 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, fr ...


Additional images

Image:Phosphatidylcholine.jpg, General structural formula of phosphatidylcholines Image:Membrane_Lipids.svg,
Membrane lipids Membrane lipids are a group of compounds (structurally similar to fats and oils) which form the double-layered surface of all cells (lipid bilayer). The three major classes of membrane lipids are phospholipids, glycolipids, and cholesterol. Lipid ...
Image:Choline metabolism-en.svg, Choline metabolism Image:Phosphatidate_skeletal.svg,
Phosphatidate Phosphatidic acids are anionic phospholipids important to cell signaling and direct activation of lipid-gated ion channels. Hydrolysis of phosphatidic acid gives rise to one molecule each of glycerol and phosphoric acid and two molecules of fatty ac ...
Image:Choline-skeletal.svg,
Choline Choline is an essential nutrient for humans and many other animals. Choline occurs as a cation that forms various salts (X− in the depicted formula is an undefined counteranion). Humans are capable of some ''de novo synthesis'' of choline but ...


References


External links

*

{{PAF signaling Phosphatidylcholines Cholinergics Phospholipids de:Phosphatidylcholin