Phosphatidylinositol: Difference between revisions

Phosphatidylinositol
Names
	Other names PI, PtdIns
Identifiers
Properties
Chemical formula	C47H83O13P
Molar mass	886.56 g/mol, neutral with fatty acid composition - 18:0, 20:4
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

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Revision as of 19:13, 8 November 2012

Phosphatidylinositol (abbreviated PtdIns, or PI) is a negatively charged phospholipid and a minor component in the cytosolic side of eukaryotic cell membranes.

The phosphatidylinositol can be phosphorylated to form phosphatidylinositol phosphate (PIP), phosphatidylinositol bisphosphate (PIP₂) and phosphatidylinositol trisphosphate (PIP₃). PIP, PIP₂ and PIP₃ are collectively called phosphoinositides.

Biosynthesis

The synthesis of phosphatidylinositol is catalyzed by phosphatidylinositol synthase and involves CDP-diacylglycerol and L-myo-inositol.^[1]

Chemistry

PI has a polar and non-polar region, making the lipid an amphiphile. Phosphatidylinositol is classified as a glycerophospholipid that contains a glycerol backbone, two non-polar fatty acid tails, a phosphate group substituted with an inositol polar head group.

The most common fatty acids of phosphoinositides are stearic acid in the SN₁ position and arachidonic acid, in the SN₂ position. Hydrolysis of phosphoinositides yield one mole of glycerol, two moles of fatty acids, one mole of inositol and one, two, or three moles of phosphoric acids, depending on the number of phosphates on the inositol rings. Phosphoinositides are regarded as the most acidic phospholipid.

Phosphoinositides

Phosphorylated forms of phosphatidylinositol are called phosphoinositides and play important roles in lipid signaling, cell signaling and membrane trafficking. The inositol ring can be phosphorylated by a variety of kinases on the three, four and five hydroxyl groups in seven different combinations. However, the two and six hydroxyl group is typically not phosphorylated due to steric hindrance.

All seven variations of the following phosphoinositides have been found in animals:

Phosphatidylinositol monophosphates:

Phosphatidylinositol 3-phosphate, also known as PtdIns3P or PI(3)P
Phosphatidylinositol 4-phosphate, also known as PtdIns4P or PI(4)P
Phosphatidylinositol 5-phosphate, also known as PtdIns5P or PI(5)P

Phosphatidylinositol bisphophosphates:

Phosphatidylinositol 3,4-bisphosphate, also known as PtdIns(3,4)P or PI(3,4)P₂
Phosphatidylinositol 3,5-bisphosphate, also known as PtdIns(3,5)P or PI(3,5)P₂
Phosphatidylinositol 4,5-bisphosphate, also known as PtdIns(4,5)P, PI(4,5)P₂ or often simply referred to as PIP₂

Phosphatidylinositol trisphophosphate:

Phosphatidylinositol 3,4,5-trisphosphate, also known as PtdIns(3,4,5)P or PI(3,4,5)P₃

These phosphoinositides are also found in plant cells, with the exception of PIP₃.^[2]

References

^ ^a ^b Mathews, Chrisotphe K. (2005). Biochemistry Third Edition. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: extra punctuation (link)
^ Muller-Roeber B, Pical C (2002). Inositol Phospholipid Metabolism in Arabidopsis. Characterized and Putative Isoforms of Inositol Phospholipid Kinase and Phosphoinositide-Specific Phospholipase C. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: extra punctuation (link)

Additional images

Membrane lipids
Phosphatidyl-inositol
Inositol
Glycerol

External links

Phosphatidylinositols at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
Phosphatidylinositol at Lipid Library

[Mathews-1] Mathews, Chrisotphe K. (2005). Biochemistry Third Edition. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: extra punctuation (link)

[Muller-Roeber_B-2] Muller-Roeber B, Pical C (2002). Inositol Phospholipid Metabolism in Arabidopsis. Characterized and Putative Isoforms of Inositol Phospholipid Kinase and Phosphoinositide-Specific Phospholipase C. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: extra punctuation (link)

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 ==Chemistry==
-PI has a polar and non-polar region, making the lipid an [[amphiphile]]. Amphiphatic lipids  demonstrate [[lipid polymorphism|polymorphic]] behavior, a current academic research topic. Phosphatidylinositol is classified as a [[glycerophospholipid]] that contains a [[glycerol]] backbone, two non-polar [[fatty acid]] tails, a [[phosphate]] group substituted with an [[inositol]] polar head group.
+PI has a polar and non-polar region, making the lipid an [[amphiphile]]. Phosphatidylinositol is classified as a [[glycerophospholipid]] that contains a [[glycerol]] backbone, two non-polar [[fatty acid]] tails, a [[phosphate]] group substituted with an [[inositol]] polar head group.
 The most common fatty acids of phosphoinositides are [[stearic acid]] in the SN<sub>1</sub> position and [[arachidonic acid]], in the SN<sub>2</sub> position. Hydrolysis of phosphoinositides yield one mole of glycerol, two moles of fatty acids, one mole of inositol and one, two, or three moles of [[phosphoric acid]]s, depending on the number of phosphates on the inositol rings. Phosphoinositides are regarded as the most acidic phospholipid.