Platelet-activating factor
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| Platelet-activating factor | |
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| Molecular formula | C26H54NO7P |
| Molar mass | 523.683 |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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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 leukocyte 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.
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[edit] 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 phosphocholine head group, just like standard phosphatidylcholine.
[edit] 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.
[edit] 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]
[edit] 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.
[edit] Antagonists
- SM-12502 is a PAF antagonist, which is metabolized in the liver by the enzyme CYP2A6. [4]
[edit] See also
[edit] References
- ^ 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. doi:. PMID 4118412.
- ^ 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:. PMID 4275800.
- ^ 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)" (abstract). J. Biol. Chem. 254 (19): 9355-8. PMID 489536.
- ^ Platelet-Activating Factor Antagonist, SM-12502, Attenuates ...
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