Phosphatides

Phospholipids were first identified by Hammerschlag and Kresling. Long and Campbell concluded that the waxy substance present in M. tuberculosis was a difficultly hydrolyzable ester of an alcohol of high molecular weight. A systematic and thorough examination of the lipids of the bacilli has been undertaken by Anderson and coworkers. He was able to differentiate between four main lipid fractions (1) phosphatides (2) acetone-soluble fats (3) waxes (4) firmly bound lipids. 

This fraction was obtained by precipitation with acetone from an ethereal extract of the cells. It formed acidic colloidal solutions with water and contained 0.37% nitrogen and 2.16% phosphorus. On hydrolysis with 5% sulfuric acid, 33.6% of water-soluble components and 65% of fatty acids were obtained. The hydrolysate contained glycerophos-phoric acid, inositol, D-mannose, and an unidentified hexose, which 

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Lipoproteins. The lipid moiety of lipoproteins is quite variable both qualitatively and quantitatively. The a-lipoprotein of serum contains glyceride, phosphatide and cholesterol to about 30 -40% of the total complex. The -lipoprotein of serum contains some glyceride but the phosphatide and cholesterol account for nearly 75% of the total. 

Triacylglycerols arise not by acylation of glycerol itself but by a sequence of steps m which the first stage is acyl transfer to l glycerol 3 phosphate (from reduction of dihy droxyacetone 3 phosphate formed as described m Section 25 21) The product of this stage IS called a phosphatidic acid... 

Hydrolysis of the phosphate ester function of the phosphatidic acid gives a diacylglycerol which then reacts with a third acyl coenzyme A molecule to produce a triacylglycerol... 

Phospholipids. Glycerides esterified by fatty acids at the 1,2 positions and a phosphoric acid residue at the 3 position constitute the class called phosphoHpids (3). In older Hterature and in commercial practice, these materials are described as phosphatides. 

Cmde oils from these processes are often of insufficient quaUty to be used directly, particularly for edible products. Impurities such as pigments, phosphatides, volatile odorous compounds, and certain metals must be removed by further processing. 

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. 

Fig. 1. Chemical stmcture of phosphatidylcholine (PC) (1) and other related phosphohpids. R C O represents fatty acid residues. The choline fragment may be replaced by other moieties such as ethanolamine (2) to give phosphatidylethanolamine (PE), inositol (3) to give phosphatidylinositol (PI), serine (4), or glycerol (5). IfH replaces choline, the compound is phosphatidic acid (6). The corresponding lUPAC-lUB names ate (1), l,2-diacyl-t -glyceto(3)phosphocholine (2), l,2-diacyl-t -glyceto(3)phosphoethanolamine (3), 1,2-diacyl-t -glyceto(3)phosphoinositol (4), 1,2-diacyl-t -glyceto(3)phospho-L-serine and (5), l,2-diacyl-t -glyceto(3)phospho(3)-t -glycetol.

The quaHty, ie, level of impurities, of the fats and oils used in the manufacture of soap is important in the production of commercial products. Fats and oils are isolated from various animal and vegetable sources and contain different intrinsic impurities. These impurities may include hydrolysis products of the triglyceride, eg, fatty acid and mono/diglycerides proteinaceous materials and particulate dirt, eg, bone meal and various vitamins, pigments, phosphatides, and sterols, ie, cholesterol and tocopherol as weU as less descript odor and color bodies. These impurities affect the physical properties such as odor and color of the fats and oils and can cause additional degradation of the fats and oils upon storage. For commercial soaps, it is desirable to keep these impurities at the absolute minimum for both storage stabiHty and finished product quaHty considerations. 

In addition to the triglycerides, the four oilseeds also contain phosphatides. For example, soybean oil containing 1.47% phosphatides consists of 48.9% phosphatidylcholine, 27.0% phosphatidylethanolamine, 21.9% phosphatidjlinositol and 2.2% phosphatidic acid (24). Total phosphatides of cottonseed and peanut kernels are estimated to be 1.5—1.9 and 0.8%, respectively (25). 

Apply bands of sample solution, overspray with [35] 12% hydrochlonc acid, leave in an atmosphere of nitrogen for 2 imn and then dry in a stream of nitrogen, then chromatograph The vinyl ether linkages in the phosphatides are hydrolyzed... 

Phosphatidic acids not only are intennediates in the biosynthesis of triacylglycerols but also are biosynthetic precursors of other members of a group of compounds called phosphoglycerides or glycerol phosphatides. Phosphorus-containing derivatives of lipids are known as phospholipids, and phosphoglycerides are one type of phospholipid. 

FIGURE 8.4 Phosphatidic acid, the parent compound for glycerophospholipids. 

Phosphatidic acid, the parent compound for the glycerol-based phospholipids (Figure 8.4), consists of 5w-glycerol-3-phosphate, with fatty acids esterified at the T and 2-positions. Phosphatidic acid is found in small amounts in most natural systems and is an important intermediate in the biosynthesis of the more common glycerophospholipids (Figure 8.6). In these compounds, a... 

Plasmalogens are ether glycerophospholipids in which the alkyl moiety is d5-a,/3-unsaturated (Figure 8.10). Common plasmalogen head groups include choline, ethanolamine, and serine. These lipids are referred to as phosphati-dal choline, phosphatidal ethanolamine, and phosphatidal serine. 

FIGURE 25.18 Synthesis of glycerolipids in eukaryotes begins with the formation of phosphatidic acid, which may be formed from dihydroxyace-tone phosphate or glycerol as shown. 

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