Glycerophosphatides

Enzymes capable of degrading glycerophosphatides are found in snake venoms, plants and bacteria. It is only recently, however, that the presence of many of these enzymes has been established beyond question in animal tissues, for in much of the earlier work bacterial contamination was not adequately controlled. 

The enzymes that hydrolyse the glycerophosphatides have been referred to variously as lecithinases, lecithases, lecitholipases, phosphatidolipases, phosphat-idases, or phosphohpases. Following the Enzyme Commission these enzymes will be referred to as phospholipases. 

A review summarizing the classical work on phosphoHpases is that of Ercoli (1940). More recent reviews have been prepared by Rossiter (1960), Kates (1960) and An SELL and Hawthorne (1964). 

---

Acid glycerophosphatides Phosphatidyl ethanolamine Lecithin Sphingomyelin Lysolecithin... 

Curstedt T, Casarett-Bruce M, Camner P. 1984. Changes in glycerophosphatides and their ether analogs in lung lavage of rabbits exposed to nickel dust. Exp Mol Pathol 41 26-34. 

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 major glycerophosphatides are esters of phosphatidic acid that have the general formula shown in Figure III-38, in which R represents a long-chain alkyl group and R an amino alcohol or inositol. Additional phosphoryl groups are esteri-... 

The plasmalogens represent an unusual type of glycerophosphatide that has been isolated from animal and plant tissues. Acid hydrolysis of these materials yields long-chain aldehydes and mono-acylated a-glycerophosphate. The long-chain aldehydes originate from vinyl ether structures. The vinyl ether group appears usually (if not always) in... 

Figure 111-38 Structures of various glycerophosphatides. The generic structure is shown at the top of the figure, and the classes differ in the structure of the R group as shown.

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. 

Fig. 2.2. Glycerophosphatids and glycolipids from plants. [Reprinted in modified form from Stumpf (1976).]...

This enzyme catalyses the reaction which synthesises an important class of phospholipids, the choline containing glycerophosphatides. 

This enzyme catalyses the synthesis of ethanolamine containing glycerophosphatides. It can be assayed radiochemically using C labelled CDP-thanolamine and solvent extraction of the reaction mixture [366]. 

This enzyme can also catalyse a reaction with 1,2-propanediol phosphate. It catalyses the reaction whereby triose phosphate is incorporated into the reactions leading to the synthesis of glycerides and glycerophosphatides. It can be assayed by u.v. spectroscopy... 

Normally, biological macromolecules which lack unpaired electrons can not be studied by e.s.r. because they do not resonate. These macromolecules can however be spin labelled (spin labelling involves the attachment of a stable and unreactive free radical to the macromolecule) and studied. Thus, lateral diffusion of glycerophosphatides in plasma membranes has been studied by labelling glycerophosphatides with a stable nitroxide free radical. 

In the pure state, cephalins are soluble in methanol, ethanol, ether, petroleum ether, chloroform, glacial acetic acid, and insoluble in acetone, but when mixed with other glycerophosphatides (phosphatidylserine, plasmalogens, etc.) they are insoluble in alcohol. It is likely that the natural cephalins are of the a t5rpe, but this has not yet been completely proved. 

---