Inositide, inositol lipids

In animal cells there are three major myo-inositol-containing phospholipids (Fig. 1) phosphatidylinositol [l-(3-sn-phosphatidyl)-D-myo-inositol) (Ptdlns)], which usually accounts for over 90% of the total inositol lipid, phosphatidylinositol-4-phosphate (Ptdlns 4-P) and phosphatidylinositol 4,5-bisphosphate (Ptdlns 4,5-P2). The polyphosphorylated inositides generally constitute 1-10% of total inositol lipids, which are themselves 6-10% of total phospholipids. The polyphosphoinositides are considered to be located on the cytoplasmic side of the plasma membrane, which places them in an ideal position to play a role in signal transduction. Ptdlns, on the other hand, is found in all cellular membranes. In some cells there is evidence for separate hormone sensitive and hormone insensitive pools of the inositol lipids [3],... 

One of the most studied examples of signaling with membrane lipids is provided by the phospho-inositide cascade, which is pictured in Fig. 11-9. Six or more phosphate esters of phosphatidylinositol (PI) are generated by the action of kinases.219 220 More than 100 extracellular signaling molecules activate specific isozyme forms of phospholipase C,221-224 releasing 20 or more different inositol phosphates from these... 

HO Phosphatidylinositol (PI) Negatively charged lipid. Inositol is the wyo-isomer. Widespread and usually minor lipid. The higher inositides, diphosphoinositide (l-(3-5 -phos-phatidyl)-L-myoinositol 4-Phosphate) and triphosphoinositide (l-(3-5n-phosphatidyl)-L-myoinositol4,5-bisphos-phate) have only been detected in animals and yeast... 

Phosphatidylinositol is also formed from CDP-diacylglycerol, though in this case only one enzyme step is involved (Figs 11.13 and 11.14). The higher inositides, diphosphoinositide and triphospho-inositide, are formed from phosphatidylinositol by two kinases (Fig. 11.13). These activities are particularly high in nervous tissue (Michell, 1975). Metabolism of other minor inositol-containing lipids has been reviewed (Hawthorne, 1982). 

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