Phospholipids, containing inositol

Com oil contains triglycerides plus phospholipids, glycolipids, phosphoinositides (phospholipids containing inositol), many isomers of sitosterol and stigmasterol (plant steroids), several tocopherols (vitamin E), waxes, unsaturated hydrocarbons such as squalene, carotenoids and chlorophyll compounds, as well as many products of decomposition, hydrolysis, oxidation, and polymerization of any of the natural constituents. ... 

Phosphatidylinositol is a phospholipid containing the inositol sugar head group. 

Phospholipids containing phosphatidyl, inositol, lecithin, serine, and ethanolamine (Stevenson 1986) are the second most abundant identifiable form of organic P in the upper layer of the subsurface. These groups contain glycerol, fatty acids, and phosphate (Sims and Pierzjinski 2005). The P in the structure is a diester, which is more susceptible to degradation in soils than monoesters. 

Inositol-containing phospholipids of the plasma membrane are the starting compounds for formation of the signal substances diacylglycerol and inositol trisphophate. The plasma membrane contains the phospholipid phosphatidyl inositol, in which the phosphate group is esterified with a cychc alcohol, myo-D-inositol (Fig. 6.3). 

On hydrolysis of the phosphatides, myo-inositol monophosphate—and, from a brain phosphatide, a diphosphate—is obtained but, these products have, in most cases, not been adequately characterized, and it is not yet known whether all phospholipids contain the same myo-inositol phosphate. It has been shown169-170 that the phosphate obtained by hydrolysis of liver phosphatide171 or soybean phosphatide172 is a mixture of myo-inositol 1- and 2-phosphates. A myo-inositol phosphate, of unknown constitution, was isolated173 from liver without previous hydrolysis apparently it occurs in the free state. 

Some 40 years ago in the halcyon days of study of the then new technique of silicic acid column chromatography of lipids, it was apparent to several investigators that there were nitrogen-free phospholipids in these samples. Also, these unique, acidic phospholipids did not contain inositol. In the usual protocol, lipids were applied to a silicic acid column in a nonpolar solvent such as hexane (or petroleum ether, b.p. 30-60°C), and elution continued with increasing amounts of diethyl ether. These solvent mixtures would elute the... 

The fatty acid components of a phospholipid may vary, and thus phosphatidyl serine, as well as most other phospholipids, represents a class of molecules rather than a single species. As a result, a single mammalian cell may contain thousands of distinct phospholipids. Phosphatidyl inositol is unusual in that it has a nearly fixed fatty acid composition. Stearic acid usually occupies the C-1 position and arachidonic acid (Section 22.6.2) the C-2 position. 

Phospholipids may consist of a backbone of glycerol esterified with two fatty acids and one molecule of choline phosphate in the position. Tn other phospholipids, the 3 position may be occupied by a molecule of ethanolamine phosphate, serine phosphate, or inositol phosphate. A phospholipid containing choline phosphate is called phosphatidylcholine one containing ethanolamine phosphate is called phosphatidylethanolamine. Generally, the fatty acids esterified as triglycerides contain up to one double bond, whereas those esterified as phos-... 

Phosphoglycerides (the major phospholipids) contain glycerol, fatty acids, and phosphate. The phosphate is esterified to choline, serine, ethanolamine, or inositol. 

Cleavage of inositol-containing phospholipids by phospholipase C is of particular regulatory importance. Phospholipase C catalyzes the release of diacyl glycerol and inositol-l,4,5-triphosphate from phosphatidyl inositol-4,5-diphosphate, a phospholipid... 

PH domains bind phosphatidyl inositol derivatives and, due to this property, are able to mediate membrane association of signal proteins. The PH domain of PL-C61 binds to phospholipids such as Ptd(Ins)P2 with high affinity and specificity. The crystal structure of the PH domain of PL-C81 with bound Ptd(Ins)P2 surprisingly has a very similar folding topology to the PTB domain that specifically binds phosphotyrosine-containing peptides (see 8.2.3 review Lemmon et al, 1996). The importance of this similarity is not understood. 

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