Acyl phosphatidyl glycerol

Phosphatidate is formed by successive acylations of glycerol 3-phosphate by acyl CoA. Hydrolysis of its phosphoiyl group followed by acyl- ation yields a triacylglycerol. CDP-diacylglycerol, the activated intermediate in the de novo synthesis of several phosphoglycerides, is formed from phosphatidate and CTP. The activated phosphatidyl unit is then transferred to the hydroxyl group of a polar alcohol, such as serine, to form a phospholipid such as phosphatidyl serine. 

After ethanolamine or choline has entered a cell, it is phosphorylated and converted to a CDP derivative. Then phosphatidylethanolamine or phosphatidylcholine is formed when diacylglycerol reacts with the CDP derivative. Triacylglycerol is produced if diacylglycerol reacts with acyl-CoA. CDP-Diacylglycerol, formed from phosphatidic acid and CTP, is a precursor of several phospholipids, for example, phosphatidyl-glycerol and phosphatidylinositol. 

Chloroplasts from photosynthetic tissues of higher plants and algae contain -3-hexadecenoate (8) (Fig. 2.13), an unusual palmitate-derived fatty acid. Desaturation of the 3-position requires light and may occur after the palmitic acid precursor is attached to the acyl moiety. This acid is found almost entirely at the 2-position of phosphatidyl glycerol (9) (Fig. 2.2). 

Only one acyl residue is cleaved by hydrolysis (cf. 3.7.1.2.1) with phospholipase A. This yields the corresponding lyso-compounds from lecithin or phosphatidyl ethanolamine. Some of these lyso-derivatives occur in nature, e. g., in cereals. Phosphatidyl glycerol is invariably found in green plants, particularly in chloroplasts ... 

Phosphatides are derivatives of phosphatidyl residues, which are based on 1,2-diacyl-sn-glycerol, which contains bound phosphoric acid on the C-3 hydroxyl. The basic compound is 3-sn-phosphatidic acid (l,2-diacyl-sn-glycerol3-phosphoricacid) (3-53). If only position C-1 (which is more often than position C-2) is occupied by an acyl, the resulting residue derived from l-acyl-s -glycerol is caUed lysophosphatidyl. The corresponding acid is 3-s -lysophosphatidic acid (l-acyl-s -glycerol3-phosphoric acid) (3-54). 

The other phospholipids can be derived from phosphatidates (residue = phosphatidyl). Their phosphate residues are esterified with the hydroxyl group of an amino alcohol choline, ethanolamine, or serine) or with the cyclohexane derivative myo-inositol. Phosphatidylcholine is shown here as an example of this type of compound. When two phosphatidyl residues are linked with one glycerol, the result is cardiolipin (not shown), a phospholipid that is characteristic of the inner mitochondrial membrane. Lysophospholipids arise from phospholipids by enzymatic cleavage of an acyl residue. The hemolytic effect of bee and snake venoms is due in part to this reaction. 

FIGURE 9.98 Events taking place in the plasma membrane on stimulation of a cell. Phospha tidylinositol (Pi) and more hi ly phosphoiylated versions of this lipid account for 2 to 8% of the lipids of the plasma membrane of eukaryotic cdIs. The inositol 1,4,5 triphosphate (fP3) moiety of phosphatidyl inositol- 4,8-di phosphate may be hydiulyitec from this lipid immediately after the cell is stimulated. For example, the stimulation of platelets by thrombin or the islets of the pancreas by glucose is followed by the release of 1P3 into the cytoplasm. In some cells, arachidonic acid is hydrolyzed from l-acyl-2-arachidonyl-glyceroL which can Support a burst of prostaglandin. synthesis. 

Glycerophospholipids (PL) are abundant lipid components found in Nature [1]. Most vegetable oils, fish oil and egg yolk are particularly rich in mixtures of phospholipids. They are characterized by the presence of a polar head and two fatty acid chains in the apolar part of the molecule. The two acyl chains mainly consist of saturated fatty acid residues in the snl position and mainly (poly)unsaturated fatty acid chains in the sn2 position. Mixtures of phospholipids at low cost are obtained from the degumming process of vegetable oils. Lecithin, the main component of the mixture, has the polar head characterized by the choline residue. It is usually defined as phosphatidyl choline (PC) and it is understood that the composition of the apolar part is composed of mixtures of fatty acid residues dependent to a large extent on the source of the raw material (fatty acid chains composition of PC from soy beans palmitic 11.6%, stearic 3.4%, oleic 4.6%, linoleic 66.4%, linolenic 8.7%). Scheme 1 shows a PC with two defined acyl chains at the glycerol backbone l-palmitoyl-2-linoleoyl-5n-glycero-3-phosphocholine (PLPC). 

You would expect to see reduced rates of synthesis of triacylglycerols, which use diacyl-glycerols as acceptors of activated acyl groups. In addition, phosphatidyl choline synthesis is dependent on the availability of diacylglycerols as acceptors of choline phosphate from CDP-choline. 

Figure 1.2 Example of lipid subclasses, which are classified based on the different hnk-ages at a certain position or a unique structural feature of a lipid class, (a) The subclasses of phosphatidyl-, plasmanyl-, and plasmenyl- are present in GPL as a result of the different linkages (i.e., ester, ether, and vinyl ether) of a fatty acyl chain to the hydroxyl group at sn- position of glycerol, (b) The different core structures of sphingoid bases in the presence or absence of a double bond between C4 and C5 carbon atoms lead to the common subclasses of sphingolipids and dihydrosphingolipids. Other less common subclasses of sphingolipids are also present due to other structures of the sphingoid bases (see Figure 1.6).

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