Lipids glycerophosphatides

Typical thin-layer chromatogram of lipids. The solvent system, hexane-diethyl ether-acetic acid (90 10 1). (1) cholesterol, (2) fatty acid, (3) triacylglycerol, (4) fatty acid methyl ester, (5) cholesterol ester, (6) glycerophosphatide, (7) sphingolipid, (8) 1,3- or 1,2-diacylglycerol, (9) 1 - or 2-monoacylglycerol. The Rf for (5), cholesterol ester, is calculated as follows ... 

Lipid standards (2°/o solutions in chloroform) a triacylglycerol (triolein), cholesterol ester (cholesterol linoleate), fatty acid (palmitoleic, oleic, etc.), fatty acid methyl ester (linolenic acid, methyl ester), a glycerophosphatide (phosphatidylcholine, phosphatidylethano-lamine, etc.), a diacylglycerol (diolein), and a monoacylglycerol (monoolein). 

An important class of lipids consists of phosphoglycerides (glycerophosphatides). These compounds may be regarded as triglycerides in which one of the acids bonded to glycerol is ortho-... 

Glycerophosphatides. These lipids are mainly acyl derivatives of a-glycerophosphoric acid and often are called phospholipids. The simplest glycerophosphatides are the phosphatidic acids, which contain a-glycerophosphoric acid esterified with two fatty acids (Fig. III-37). Small quantities of phosphatidic acids have been isolated from a wide variety of plant and animal tissues. It is doubtful that these compounds exist in large amounts in tissues, because more complex glycerophosphatides are readily hydrolyzed by enzymes that are widely distributed in such tissues, yielding phosphatidic acids. Phosphatidic acid is a crucial intermediate in the biosynthesis of phospholipids. 

The glycerophosphatides usually contain substantial amounts of highly unsaturated fatty acids that undergo rapid autoxidation catalyzed by Cu2+ or Fe3+ salts. These salts tend to be carried along by lipids into the organic phase. Thus, lipid extractions may have to be made in a nitrogen atmosphere in the cold and may require the use of peroxide-free solvents or antioxidants. 

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. 

Recent isotope incorporation studies by a number of workers have indicated increased turnover of muscle membrane lipids following denervation. These include increased incorporation of labeled phosphate and glycerol into glycerophosphatides (B17), increased turnover of... 

Lipids may be polar or nonpolar (amphipathic). Polar lipids have limited solubility in water because they are amphipathic, i.e., they possess hydrophilic and hydro-phobic regions in the same molecule. Major polar lipids include fatty acids, cholesterol, glycerophosphatides, and glycosphingolipids. Very short chain fatty acids and ketone bodies are readily soluble in water. Nonpolar lipids serve principally as storage and transport forms of lipid and include triacylglycerols (also called triglycerides) and cholesteryl esters. 

O Brien JS, Eillerup DL, Mead JF. Quantification and fatty acid and fatty aldehyde composition of ethanolamine, choline, and serine glycerophosphatides in human cerebral gray and white matter. J Lipid Res 1964 5 329-338. 

The parent compound of the glycerophosphatides is L-a-phosphatidic acid (I), a substance now known to be an important intermediate in the biosynthesis of most of these lipids. 

The degradation of the glycerophosphatides may be brought about by a variety of enzymes with a wide distribution in nature. The activity of many of these enzymes is altered considerably (1) by the addition of substances, such as ethyl ether, that can penetrate into the lipid micelle and alter the spacing of the molecules oriented at the lipid-water interface and (2) by the presence in the water phase of polyvalent cations or anions that can modify the surface charge in the... 

The behaviour of other organ lipids is variable. A slight increase in glycerophosphatide and triglyceride content is frequent but insignificant when compared with the other fractions. It probably represents a non-specific, secondary change. 

Study of lipid fractions from liver, kidney and brain showed liver cholesterol ester fatty acids to contain the highest proportion of phytanic acid with over 60% significant amounts of the acid were also found in liver and kidney triglycerides. Phytanic acid in brain was present only in the aceton soluble fraction, and, in small concentration, in fatty acids of glycerophosphatides (see table 5). 

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