Phosphatidylinositol fatty acid composition

Some of the earlier data tabulated by Morrison (1970) on the fatty acid compositions of milk phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin are shown in Table 4.10. Included are analyses by Boatman et al. (1969) on phosphatidylethanolamine and phosphati-dylserine and by Bracco et al (1972) on phosphatidylinositol. The differences in composition between the samples of phosphatidylethanolamine and -serine can be attributed primarily to differences in metabolism. 

The complex lipids in milk fat are comprised of the phosphoglycerides, phosphatidyl choline, phosphatidyl serine, phosphatidyl ethanolamine, phosphatidylinositol and plasmalogens. Also, the non-glyceride phospholipid, sphingomyelin, occurs in important amounts (Jensen, 2002). Bitman and Wood (1990) described the distribution of phospholipid classes in bovine milk and their fatty acid composition. The phospholipids comprise about 1% and cholesterol 0.4—0.5% of the total milk fat. These occur almost completely in the milk fat globule membrane. 

The fatty acid composition of hazelnut oil is as follows 78-83% oleic acid, 9-10% linoleic acid, 4—5% palmitic acid, and 2-3% stearic acid as well as other minor fatty acids (Table 3) (1, 22). Parcerisa et al. (23) examined lipid class composition of hazelnut oil, showing that triacylglycerols constituted 98.4% of total lipids, glycolipids comprised 1.4% of total hpids, and trace amounts (<0.2%) of phosphatidylcholine and phosphatidylinositol were also present. Hazelnut oil contains 1.2-1.14 g/kg of phytosterols primarily in the form of p-sitosterol and is a very good source of a-tocopherol (382-472 mg/kg) (1, 22). The main odorant in... 

Almost all body cells contain phospholipids. The common animal phospholipids are made of sphingomyelin, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), and other glycerol phospholipids of complex fatty acid composition. PC, formerly referred to as lecithin, PE, formerly referred to as cephalin, and PS are by far the most predominant phospholipids from most animal sources. As constituents of cell walls and active participants in metabolic processes, they appear to be essential to life (8). 

The fatty acid components of phospholipids may vary, and thus cardi-olipin, as well as most other phospholipids, represents a class of molecules rather than a single species. Asa result, a single mammalian cell may contain thousands of distinct phospholipids. Phosphatidylinositol is unusual in tliat it has a nearly fixed fatty acid composition. Stearic acid usucilly occupies the C-1 position and arachidonic acid the C-2 position. 

Helmkamp (1980a) studied the effect of the fatty acid composition of the acceptor lipid on the stimulation of phosphatidylinositol transfer from rat liver microsomes to phosphatidylcholine vesicles by bovine brain exchange protein. Acceptor vesicles containing egg phosphatidylcholine or dioleoyl phosphatidylcholine gave approximately the same transfer activity, whereas dielaidoyl phosphatidylcholine or dimyristoyl phosphatidylcholine vesicles produced lower transfer rates. Zborowski and Demel (1982) used the same protein and measured the rate of transfer of phosphatidylinositol from a monolayer to phosphatidylcholine vesicles. Vesicles of egg, dioleoyl, dielaidoyl, and dipalmitoyl phosphatidylcholine, even below its phase transition temperature, all gave equivalent transfer rates. However, a reduced rate was found when dimyristoyl and dilin-oleoyl phosphatidylcholine, and other phosphatidylcholines with two polyunsaturated fatty acids, were used. Table IV shows a comparison of the transfer activities measured in the two assays. The transfer rates are expressed as a percent of the transfer rate obtained with egg phosphatidylcholine acceptor vesicles. 

Broekman, M.J., Ward, J.W. and Marcus, A.J. (1981). Fatty acid composition of phosphatidylinositol and phosphatidic acid in stimulated platelets. J. Biol Chem., 256, 8271-8274... 

The fact that phosphatidylinositol has a fatty acid composition which is very different from that of the other phospholipids of pancreas was used to test whether the newly-formed phosphatidic acid in the stimulated tissue was derived from phosphatidylinositol (Geison et al., 1976). The structure of phosphatidylinositol from other mammalian tissues has been shown to be 1-stearoyl, 2-arachidon-oyl-sn-glycero-3-phosphorylinositol (Holub Kuksis, 1971 Baker Thompson, 1972), We find that this fatty acid composition is also typical of pancreas phosphatidylinositol. Lipid-soluble products of phosphatidylinositol which retain the diacylglycerol moiety should therefore contain stearic and arachidonic acids in equal proportions. In pancreas tissue incubated with acetylcholine, there is stoichiometry between the amounts of stearic and arachidonic acids which are lost from the phosphatidylinositol fraction and the amounts which appear in the phosphatidic acid fraction. The newly-formed phosphatidic acid appears therefore to have the same fatty acid composition as the phosphatidylinositol which is broken down. It presumably contains the 1-stearoyl, 2-arachidonoyl glycerol moiety which was originally in phosphatidylinositol. I shall use the prefix (18 0,20 4) to denote lipids which contain this moiety. The (18 0,20 4)phosphatidic acid which is formed in stimulated tissue is a novel species there is very little stearic acid and arachidonic acid in the phosphatidic acid from unstimulated pancreas. 

The rate of production of DAG in the cell does not occur linearly with time, but rather it is biphasic. The first peak is rapid and transient and coincides with the formation of IP3 and the release of Ca2+ this DAG is therefore derived from the PI-PLC catalyzed hydrolysis of phosphatidylinositols [1]. There is then an extended period of enhanced DAG production that is now known to be derived from the more abundant phospholipid phosphatidylcholine (PC), which has a different composition of fatty acid side chains [9]. Although DAG may be generated directly from PC through the action of PC-PLC, it can also be formed indirectly from PC. In this pathway, PC is first hydrolyzed by PLD to give choline and phosphatidic acid, which is then converted to DAG by the action of a phos-phatidic acid phosphatase [10,11 ]. 

Phosphatidylcholine and phosphatidylinositol from rat liver were separated into molecular species under exactly the same conditions. Indeed, fractions identical in composition were obtained, although the relative proportions were rather different because of variations in fatty acid profiles, as expected. After modifying the mobile phase to 30 mM choline chloride in methanol-25 mM K2HP04-acetonitrile-acetic acid (90.5 7 2.5 0.8 by volume), molecular... 

Analogous to normal phase HPLC, CE has been successfully used for separation of the various types of phospholipids phosphatidylcholine, phosphatidylethanolamine, phos-phatidylserine, phosphatidylinositol, and phosphatidic acid. The elution order is affected by buffer strength and composition. Analogous to reversed-phase HPLC, some separation according to the nature of the fatty acid substituents is seen with MEKC. 

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