Lysophosphatidyl inositol

A chloroform/methanol/water system is appropriate for the separation of an acidic fraction. If the solvent compositions are not optimized, the phospholipids and glycolipids are eluted at the solvent front or in the column contents. When we chose a suitable solvent, acidic phospholipids (phosphatidic acid, phosphatidylserine, phosphatidylinositol, lysophosphatidyl-inositol, and lysophosphatidylserine) were satisfactorily separated between the solvent front and the column contents (Fig. 2A). Samples (2 mg each) of the acidic fraction of human brain lipids was applied to TC-CCC by using the chloroform/methanol/water (5 4 3) solvent system. Aliquots of each fraction were spotted and developed by HPTLC. 

Like glycolipids, phospholipids are also a elass of polar lipids. Data in Table 3.2 show that phospholipids in natural rubber are normally below 0.6% w/w. A recent study showed that the major components were phosphatidyl choline (PC) and lysophosphatidyl choline (LPC), as shown in Table 3.5. Other minor components were phosphatidyl ethanolamine (PE), phosphatidyl inositol (PI), lysophosphatidyl inositol (LPI), and metal phosphatidates (MP) or phosphatidic acid (PA). Unlike neutral lipids and glycolipids, the acyl components of phospholipids normally contain very low levels of furanoic acid, except for certain rubber clones. The isolated fatty acids are mainly palmitic, stearic, oleic and linoleic acids. ... 

Table 1 shows that lysophosphatidyl inositol can be readily acylated by rat brain microsomes with any of a number of acyl CoA thioesters. There is a general preference for unsaturated over saturated thioesters but, more strikingly, there is a high selectivity for arachidonoyl CoA which under certain condition of incubation is some 4-8 times more active in acylating the lysolipid than the other thioesters. The eicosatrienoic species used in this series is the precursor of arachidonate with the same arrangement of double bonds at positions 8, 11 and 14. The marked difference... 

The 2 vitro data together with other vivo data (1) lead us to conclude that the deacylation and reacylation sequence must be an important means for establishing arachidonoyl-containing species of phosphatidyl inositol. There are, however, still some elements of the picture to be filled in. For example, there is minimal information about phospholipase A activity towards phosphatidyl inositol and, secondly, the presence of lysophosphatidyl inositol has yet to be demonstrated in fresh tissues which, of-course, is a requisite for the proposed deacylation - reacylation reactions. If lysophosphatidyl inositol does occur in tissues it must undoubtedly be present in very low concentrations. 

Keenan and Hokin (1964) showed that lysophosphatidyl inositol occurs in pigeon pancreas and that this compound may be esterified by an acyltransferase reaction analogous to the enzymic acylation of lysolecithin (Reaction 16). 

Although the nuclear membrane s proteins have been fractionated by gel electrophoresis and their amino acid composition has been studied, their function remains unknown. However, it is certain that they are not histones. Although the quantitative content of phospholipids in the nuclear membrane is not certain, it is estimated that 50-60% of the phospholipids found in the nucleus are associated with the membrane. They include cardiolipin, phosphatidyl ethanolamine, phosphatidyl serine, phosphatidyl inositol, phosphatidyl choline, sphingomyelin, and lysophosphatidyl choline. Of course, as in most cellular membranes, their function remains to be determined. 

From the standpoint of practical TLC, this chapter considers the following simple hpids free sterols acyl-, diacyl-, and triacylglycerols free fatty acids methyl esters sterol esters and the following polar lipids phosphatidyl choline, lysophosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl serine, phosphatidyl inositol, sphingoipyelin, cerebrosides, and sulfatides. 

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