Phosphoglycerides. Phosphate esters

Mono-, di- and triacylglycerols may all be measured by determination of the amount of glycerol released by hydrolysis. The lipid is first extracted into chloroform-methanol (2 1) and saponification is performed under conditions that will not affect any phosphate ester bonds, otherwise glycerol originating from phosphoglycerides would also be measured. Heating at 70°C for 30 min with alcoholic potassium hydroxide (0.5 mol l-1) has been shown to be satisfactory. However, the phospholipids may be removed prior to saponification either by extraction or by adsorption on activated silicic acid. 

Two main types of lipids occur in biological membranes phospholipids and sterols. The predominant phospholipids in most membranes are phosphoglycerides, which are phosphate esters of the three-carbon alcohol, glycerol. A typical structure is that of phosphatidylcholine (lecithin) ... 

Phospholipase D Behavior. While this enzyme shows no stereospecificity in its attack on the ethanolamine phosphoglycerides, its action in releasing free ethanolamine and a phosphatidic acid provides very clear evidence that the ethanolamine was attached to the parent molecule via a phosphate ester bond. Again, the same protocols and enzyme sources illustrated in Chapter 4 for phosphatidylcholine can be applied very easily to the ethanolamine phosphoglycerides. 

Phosphoglycerides such as lecithin and cephalin are closely related to fats. The glycerol backbone in these molecules is esterified to two fatty acids (one saturated and one unsaturated) and to one phosphate ester. Sphingolipids, another major class of phospholipids, have an amino alcohol such as sphingosinc for their backbone. These compounds are important constituents of cell membranes. 

CDP-diacylglycerol and the CDP-alcohols are activated intermediates that allow the formation of phosphate ester bonds in phosphoglycerides, a process that is otherwise highly... 

Phosphoglycerides are hydrolysed by naturally occurring enzymes, the phospholipases, which specifically cleave certain bonds within the molecule to release fatty acids, the phosphate ester, the alcohol and glycerol. The release of choline, when followed by further oxidative breakdown, has been considered to be responsible for the development of fishy taints by the release of the trimethyl amine group or its oxide currently these taints are considered to be the result of fat oxidation and not of lecithin breakdown. 

The phosphoglycerides combine within the same molecule both the hydrophilic (water-loving) phosphate ester groups and the hydrophobic fatty acid chains. They are therefore surface-active and play a role as emulsifying agents in biological systems, for example in the duodenum. Their surface-active nature also explains their function as constituents of various biological membranes. 

The major phosphoglycerides are derived from phosphatidate by the formation of an ester bond between the phosphate group of phosphatidate and the hydroxyl group of one of several alcohols. The common alcohol moieties of phosphoglycerides are the amino acid serine, ethanolamine, choline, glycerol, and the inositol. 

The major phosphoglycerides are derived from phosphatidate by the formation of an ester bond between the phosphate group of... 

Fischer projection formula, 974 3-phosphate, 1003 l-GIyceraldehyde, 974 Glycerol. See also Phosphoglycerides esters, 788, 795,1017-1018, 1022-1023, 1043... 

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