Inositol

I**nositol** or **cyclohexane-1,2,3,4,5,6-hexol** is a chemical compound with formula C6H12O6 or (-CHOH-)6, a sixfold alcohol (polyol) of cyclohexane. It exists in nine possible stereoisomers, of which the most prominent form, widely occurring in nature, is **//cis//-1,2,3,5-//trans//-4,6-cyclohexanehexol**, or **//myo//-inositol** (former name **meso**-inositol Inositol is a carbohydrate, though not a classical sugar. It has a taste that is said to be half the sweetness of table sugar (sucrose). M//yo//-Inositol plays an important role as the structural basis for a number of secondary messengers in eukaryotic cells, including [|inositol phosphates], [|phosphatidylinositol] (PI) and [|phosphatidylinositol phosphate] (PIP) lipids.

Isomers and structure
The isomer //myo//-inositol is a [|meso compound] possessing an optically inactive plane of symmetry through the molecule, and //meso//-inositol is an obsolete name that refers to //myo//-inositol. Besides //myo//-inositol, the other naturally occurring stereoisomers (though in minimal quantities) are ** [|//scyllo//] -**, ** [|//muco//] -**, ** [| D -//chiro//] -**, and ** [|//neo//-inositol] **. The other possible isomers are ** [|//allo//] -**, ** [|//epi//] -**, and ** [|//cis//-inositol] **. As their name denotes, the two //chiro// inositols are the only pair of inositol [|enantiomers], but they are enantiomers of each other, not of //myo//-inositol. In its most stable conformational geometry, the //myo//-inositol isomer assumes the [|chair conformation], which puts the maximum number of hydroxyls to the equatorial position, where they are farthest apart from each other. In this conformation the natural //myo// isomer has a structure in which five of the six [|hydroxyls] (the 1st, 3rd, 4th, 5th, and 6th) are [|equatorial], whereas the 2nd hydroxyl group is [|axial]. [|[8]]
 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/0/0b/Myo-inositol.svg/120px-Myo-inositol.svg.png width="120" height="120" caption="Myo-inositol.svg" link="http://en.wikipedia.org/wiki/File:Myo-inositol.svg"]] || [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/5/50/Scyllo-inositol.svg/120px-Scyllo-inositol.svg.png width="120" height="120" caption="Scyllo-inositol.svg" link="http://en.wikipedia.org/wiki/File:Scyllo-inositol.svg"]] || [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Muco-inositol.svg/120px-Muco-inositol.svg.png width="120" height="120" caption="Muco-inositol.svg" link="http://en.wikipedia.org/wiki/File:Muco-inositol.svg"]] || [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/5/5f/Chiro-inositol.svg/250px-Chiro-inositol.svg.png width="250" height="125" caption="Chiro-inositol.svg" link="http://en.wikipedia.org/wiki/File:Chiro-inositol.svg"]] ||
 * //myo//- || //scyllo//- || //muco//- || //chiro//- ||
 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Neo-inositol.svg/120px-Neo-inositol.svg.png width="120" height="120" caption="Neo-inositol.svg" link="http://en.wikipedia.org/wiki/File:Neo-inositol.svg"]] || [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/7/74/Allo-inositol.svg/120px-Allo-inositol.svg.png width="120" height="120" caption="Allo-inositol.svg" link="http://en.wikipedia.org/wiki/File:Allo-inositol.svg"]] || [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Epi-inositol.svg/120px-Epi-inositol.svg.png width="120" height="121" caption="Epi-inositol.svg" link="http://en.wikipedia.org/wiki/File:Epi-inositol.svg"]] || [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/7/73/Cis-inositol.svg/120px-Cis-inositol.svg.png width="120" height="120" align="center" caption="Cis-inositol.svg" link="http://en.wikipedia.org/wiki/File:Cis-inositol.svg"]] ||
 * //neo//- || //allo//- || //epi//- || //cis//- ||

Synthesis
//myo//-Inositol is synthesized from [|glucose-6-phosphate] (G-6-P) in two steps. First, G-6-P is [|isomerised] by an [|inositol-3-phosphate synthase] enzyme (called ISYNA1) to //myo//-inositol 1-phosphate, which is then dephosphorylated by an [|inositol monophosphatase] enzyme (called IMPase 1) to give free //myo//-inositol. In humans most inositol is synthesized in the kidneys, in typical amounts of a few grams per day

Function
Inositol and some of its mono and polyphosphates function as the basis for a number of signaling and secondary messenger molecules. They are involved in a number of biological processes, including:
 * [|Insulin] [|signal transduction][|[9]]
 * [|Cytoskeleton] assembly
 * Nerve guidance ( [|Epsin] )
 * [|Intracellular] [|calcium] (Ca2+) concentration control [|[10]]
 * Cell [|membrane potential] maintenance [|[11]]
 * [|Serotonin] activity modulation
 * Breakdown of [|fats] and reducing blood [|cholesterol][|[12]]
 * [|Gene expression][|[13]][|[14]]