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Information about Platelet Activating Factor

Platelet-activating factor
Identifiers
PubChem108156
MeSHPlatelet+Activating+Factor
Properties
Molecular formulaC26H54NO7P
Molar mass523.683
Except where noted otherwise, data are given for
materials in their standard state
(at 25 C, 100 kPa)
A platelet-activating factor, also known as a PAF, PAF-acether or AGEPC (acetyl-glyceryl-ether-phosphorylcholine) is a potent phospholipid activator and mediator of many leucocyte functions, including platelet aggregation, inflammation, and anaphylaxis.

It is produced in response to specific stimuli by a variety of cell types, including neutrophils, basophils, platelets, and endothelial cells.

Chemistry

Several molecular species of platelet-activating factor have been identified which vary in the length of the O-alkyl side chain.
  • Its alkyl group is connected by an ether linkage at the C1 carbon to a sixteen carbon chain.
  • The acyl group at the C2 carbon is an acetate unit (as opposed to a fatty acid) whose short length increases the solubility of PAF, allowing it to function as a soluble signal messenger.
  • The C3 has a phosphate group, just like standard glycerophospholipids.

Function

It is an important mediator of bronchoconstriction.

It causes platelets to aggregate and blood vessels to dilate. At a concentration of 10^-12 M, PAF causes life threatening inflammation of the airways to induce asthma like symptoms.

Toxins such as fragments of destroyed bacteria induce the synthesis of PAF, which causes a drop in blood pressure and reduced volume of blood pumped by the heart, which leads to shock and maybe death.

History

It was discovered by French immunologist Jacques Benveniste in the early 1970s.[1][2] Its structure was elucidated by Constantinos A. Demopoulos in 1979.[3]

Biosynthesis and degradation

PAF is biosynthesized from lysophosphatidylcholine (LPC) and acetyl CoA by the enzyme LPC acetyltransferase (LPCAT).

It is degraded (thereby terminating its capacity to act as a signaling molecule) by a group of enzymes called PAF acetylhydrolases (PAFAHs) which are related to phospholipase A2.

See also

References

1. ^ Benveniste J, Henson PM, Cochrane CG (1972). "Leukocyte-dependent histamine release from rabbit platelets. The role of IgE, basophils, and a platelet-activating factor". J. Exp. Med. 136 (6): 1356-77. PMID 4118412. 
2. ^ Benveniste J (1974). "Platelet-activating factor, a new mediator of anaphylaxis and immune complex deposition from rabbit and human basophils". Nature 249 (457): 581-2. DOI:10.1038/249581a0. PMID 4275800. 
3. ^ Demopoulos CA, Pinckard RN, Hanahan DJ (1979). "Platelet-activating factor. Evidence for 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine as the active component (a new class of lipid chemical mediators)". J. Biol. Chem. 254 (19): 9355-8. PMID 489536. 

External links

 •  • [ e]
Lipids: phospholipids
Glycerol backbone (Glycerophospholipids/Phosphoglycerides)Phosphatidylethanolamine/Cephalin - Phosphatidylcholine - Dipalmitoylphosphatidylcholine - Cardiolipin - Phosphatidylserine - Ether lipids (Plasmalogen, Platelet-activating factor) - Phosphatidylinositol - Glycophosphatidylinositol - PIP1 - PIP2 (3,4, 3,5, 4,5) - PIP3
Sphingosine backboneSphingomyelin
OtherPhosphatidate
 •  • [ e]
Autacoids
Angiotensin - Eicosanoid - Histamine - Kinin - Platelet-activating factor - Serotonin
PubChem is a database of chemical molecules. The system is maintained by the National Center for Biotechnology Information (NCBI), a component of the National Library of Medicine, which is part of the United States National Institutes of Health (NIH).
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Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. Created and updated by the United States National Library of Medicine (NLM), it is used by the MEDLINE/PubMed
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A chemical formula is a concise way of expressing information about the atoms that constitute a particular chemical compound. A chemical formula is also a short way of showing how a chemical reaction occurs.
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Molar mass, symbol M,[1] is the mass of one mole of a substance (chemical element or chemical compound).[2] It is a physical property which is characteristic of each pure substance.
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standard state of a material is its state at 1 bar (100 kilopascals exactly). This pressure was changed from 1 atm (101.325 kilopascals) by IUPAC in 1990.[1] The standard state of a material can be defined at any given temperature, most commonly 25 degrees Celsius,
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U indicates the uncharged hydrophobic portion of the molecule, highlighted in blue.]]

Phospholipids are a class of lipids, and a major component of all biological membranes, along with glycolipids, cholesterol and proteins.
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Platelets, or thrombocytes, are the cell fragments circulating in the blood that are involved in the cellular mechanisms of primary hemostasis leading to the formation of blood clots.
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Inflammation (Latin, inflammatio, to set on fire) is the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants.
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MeSH D000707 Anaphylaxis is an acute systemic (multi-system) and severe Type I Hypersensitivity allergic reaction in humans and other mammals. The term comes from the Greek words ana (against) and phylaxis (protection).
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Neutrophil granulocytes, generally referred to as neutrophils, are the most abundant type of white blood cells and form an integral part of the immune system. Their name arrives from staining characteristics on hematoxylin and eosin (H&E) histological preparations.
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Basophils are the least common of the granulocytes, representing about 0.01% to 0.3% of circulating leukocytes (white blood cells). They contain large cytoplasmic granules which obscure the cell nucleus under the microscope.
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Platelets, or thrombocytes, are the cell fragments circulating in the blood that are involved in the cellular mechanisms of primary hemostasis leading to the formation of blood clots.
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endothelium is the thin layer of cells that line the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. Endothelial cells line the entire circulatory system, from the heart to the smallest capillary.
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side chain in organic chemistry and biochemistry is a part of a molecule that is attached to a core structure. An R group is a generic label for a side chain which can be anything; however, it is typically stable and covalently linked to the adjoining atom.
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An alkyl is a univalent (or free) radical containing only carbon and hydrogen atoms arranged in a chain. The alkyls form a homologous series with the general formula CnH2n+1.
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Ether is the general name for a class of chemical compounds which contain an ether group — an oxygen atom connected to two (substituted) alkyl or aryl groups — of general formula R–O–R'.
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An acetate, or ethanoate, is a salt or ester of acetic acid.

Acetate anion

The acetate anion, [C2H3O2]−, is a carboxylate and is the conjugate base of acetic acid.
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Types of Fats in Food
  • Unsaturated fat
  • Monounsaturated fat
  • Polyunsaturated fat
  • Trans fat
  • Omega: 3, 6, 9

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Glycerophospholipids or phosphoglycerides are glycerol-based phospholipids. They are the main component of biological membranes.

Structures

The term glycerophospholipid signifies any derivative of sn-glycero-3-phosphoric acid that contains at least one O-acyl, or
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Bronchoconstriction is the constriction of the airways in the lungs due to the tighting of surrounding smooth muscle, with consequent coughing, wheezing, and shortness of breath. Bronchoconstriction can also be due to an accumulation of thick mucus.
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Asthma
Classification & external resources

ICD-10 J 45.
ICD-9 493

OMIM 600807
DiseasesDB 1006
MedlinePlus 000141
eMedicine med/177   emerg/43

MeSH C08.127.
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toxin (Greek: τοξικόν, toxikon, lit. (poison) for use on arrows) is a poisonous substance produced by living cells or organisms.
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Blood pressure (strictly speaking: vascular pressure) refers to the force exerted by circulating blood on the walls of blood vessels, and constitutes one of the principal vital signs.
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Shock
Classification & external resources

ICD-10 many incl. R 57.
ICD-9 785

DiseasesDB 12013
MedlinePlus 000039
eMedicine emerg/531   med/285 emerg/533

MeSH D012769

For other uses, see Shock.

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Jacques Benveniste was a French immunologist (March 12, 1935 - October 3, 2004). In 1979 he published in the French Compte rendus de l'Académie des Sciences a well-known paper where he contributes to the description of the structure of the platelet-activating factor and
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Phosphatidylcholine or Polyenylphosphatidylcholine [1] is a phospholipid which is the major component of a phosphatide fraction which may be isolated from either egg yolk (in Greek lekithos - λεκιθος) or soy beans from which it is mechanically
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Acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main use is to convey the carbon atoms within the acetyl group to Krebs Cycle to be oxidized for energy production.
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Acyltransferase like 2 (or lysophospatidylcholine acyltransferase) is an enzyme which converts lysophospatidylcholine and phosphatidylcholine.

See also

  • platelet-activating factor


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PAF acetylhydrolase is an enzyme which catabolizes platelet-activating factor.

Genes

  • PAFAH1B1 , PAFAH1B2 , PAFAH1B3 , PAFAH2

External links

  • MeSH PAF+acetylhydrolase
  • EC 3.1.1.

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Phospholipases A2 (PLA2s) EC 3.1.1.4 are enzymes that specifically hydrolyze the sn-2 fatty acid acyl bond of phospholipids, producing a free fatty acid and a lyso-phospholipid.
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