Inositol phosphatides

Lecithin. Lecithin [8002-43-5] (qv) is a mixture of fat-like compounds that includes phosphatidyl choline, phosphatidyl ethanolamines, inositol phosphatides, and other compounds (37). Commercial lecithin was originally obtained from egg yolks, but is now extracted from soybean oil. Lecithin is used in many products, including margarine, chocolate, ice cream, cake batter, and bread. 

Inositol phosphatides have another role in formation of microfilaments of the cytoske-leton. 

The expected incorporation of mi/o-inositol into phospholipids has been observed in two31 126 and in kidney preparations in vitro,138 and some progress has been made toward understanding the enzymic mechanism involved.101 1 138,139 It appears that the inositol is neither phosphorylated nor converted to a coenzyme prior to incorporation. Hokin and Hokin140 have made the interesting observation that the turnover of myo-inositol in the monophosphoinositide of brain and pancreas slices is stimulated by acetylcholine. The effects of various drugs on this turnover have been studied by other workers. It has been postulated that the decomposition and resynthesis of inositol phosphatide is a part of the membrane-transport process.140... 

Folch, J. (1942) Brain cephalin, a mixture of phosphatides. Separation from it of phosphatidyl serine, phosphatidyl ethanolamine and a fraction containing an inositol phosphatide, J. Biol. Chem. 146, 35-44. 

Acid hydrolyses are usually carried out by refluxing in 6 N aqueous hydrochloric acid (constant boiling) or 5 to 10% solutions of HC1 in methanol (to promote solubility) for 4 to 30 hr, depending on the lipid in question. Most glycerophosphatides are hydrolyzed by acid to fatty acids, glycerophosphate, and the free base, just as with alkali. However, inositol phosphatides initially yield inositol phosphate and diglycerides on acid hydrolysis. Hydrochloric acid is easily removed by vacuum, which makes chromatographic examination of the hydrolysis products easier. 

Phosphatidyl choline (lecithin), phosphatidyl serine, phosphatidyl glycerol, phosphatidyl inositol, phosphatidic acid. 

Biosynthesis of phosphatidylinositols and phosphatidylglycerols. Enzymes (1) glycerol kinase (2) acyltransferases (3) phosphatidate cytidyltransferase (4) CDP-diacylglycerol inositol phosphatidate transferase (5) CDP-diacylglycerol in-glycerol-3-phosphate phosphatidate transferase (6) phosphatase (7) phosphatidylglycerol CDP-diacylglycerol phosphatidate transferase. 

Cultivar Phosphatidylcholine (%) Phosphatidyl-ethanolamine (%) Phosphatidyl-inositol (%) Phosphatidic acid (%)... 

Inositol (e.g., 1 or 2% of the diet) lessens the effect of the polyunsaturated fatty acids in encephalomalacia and in exudative diathesis. Whether this has to do with incorporation of the fatty acids into inositol phosphatides has not been investigated. 

Klenk, E., and U. W. Hendricks An inositol phosphatide containing carbohydrate isolated from human brain. Biochim. biophys. Acta (Amst.) 50, 602— 3 (1961). 

Phosphatidyl choline (lecithin). Phosphatidyl serine. Phosphatidyl glycerol. Phosphatidyl inositol, Phosphatidic acid, sphingomyelin, DGDG dihexadecyl phosphate, dialkyl dimethyl ammonium salts... 

It is noteworthy that diglyceride residues can also be linked with CDP. The product is an active derivative capable of reacting with inositol to give an inositol phosphatide. Cardiolipin, a bisphosphatidylglycerol, also might arise by a transfer of phosphatide groups. 

The fatty acid composition of the serine phosphoglycerides was relatively simple (Marcus et al., 1962). The main saturated fatty acid was stearic, which was present in amounts equal to the sum of the unsaturated fatty acids, oleic and arachidonic. There was very little plasmalogen in the serine phosphoglycerides, as was also noted by Speer and Ridgway (1962). The fatty acid and aldehyde composition of inositol phosphatide (PI) was quite similar to that of PS. There were trace amounts of serine phosphoglycerides in the PI fractions, but it was felt that they did not contribute to the overall pattern. In contrast to the cephalin fractions, the lecithins contained large quantities of palmitic and oleic acids. As with platelet PS, the plasmalogen component in the lecithin fractions was small. 

Inositol phosphatides, or phosphoinositides, are found in plants, animals, and micro-organisms and comprise 2 to 9% of the total phosphatides of animal tissues. On hydrolysis they yield wyo-inositol, myo-inositolphosphate, glycerol, fatty acids and, in many cases, various sugars. In the few cases which have been investigated the phosphate group appears to be attached to carbon 3 of wyo-inositol . A more detailed discussion of the phosphoinositides appears in another chapter. 

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