Inositol triphosphate

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CASNo = 85166-31-0
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PubChem = 55310
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Formula = C6H15O15P3
MolarMass = 420.096
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Inositol trisphosphate or inositol 1,4,5-trisphosphate (also commonly known as triphosphoinositol; abbreviated InsP₃ or IP₃), together with diacylglycerol, is a secondary messenger molecule used in signal transduction in biological cells. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP₂), a phospholipid that is located in the plasma membrane, by phospholipase C.

Mechanism

IP₃ binds to and activates the InsP₃ receptor on the membrane of the endoplasmic reticulum (ER), and sarcoplasmic reticulum (SR) opens a calcium channel, resulting in the release of Ca²⁺ into the cytoplasm, and sarcoplasm respectively. [Ferris CD, Snyder SH. IP3 receptors. Ligand-activated calcium channels in multiple forms. Adv Second Messenger Phosphoprotein Res. 1992;26:95-107. PMID 1329896] This increase in Ca²⁺ activates the ryanodine receptor-operated channel on the SR, leading to a further increase in the Ca²⁺.

Function

Human

Its main functions are to mobilize Ca²⁺ from storage organelles and to regulate cell proliferation and other cellular reactions.

In smooth muscle cells, for example, the increase in concentration of cytoplasmic calcium results in the contraction of the muscle cell. [Somlyo AP, Somlyo AV. Signal transduction and regulation in smooth muscle. Nature. 1994 Nov 17;372(6503):231-6. PMID 7969467] . "For further reading of Ca²⁺-mediated functions, see functions of calcium in humans."

Fruit fly

For example, in the fruit fly "Drosophila", InsP₃ is used for intracellular transduction of light recognition in eye cells.

Sea urchin eggs

The slow block to polyspermy in the sea urchin is mediated by the phosphatidyl inositol diphosphate (PIP₂) secondery messenger system. Activation of the binding receptors activates phospholipase C, witch cleaves PIP₂ in the egg plasma membrane, releasing inositol triphosphate (IP₃ into the egg cell cytoplasm. IP₃ diffuses to the endoplasmic reticulum, where it opens calcium channels.

ee also

* inositol
* inositol phosphate
* myo-inositol
* inositol pentakisphosphate
* inositol hexaphosphate
* inositol triphosphate receptor
* ITPR1
* ITPKC

External links

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References