Phosphatidylethanolamine Phosphatidylglycerol

The architecture of the CM bilayer is symmetrical, with an equal distribution of the lipids (exclusively phospholipids, mainly phosphatidylethanolamine, phosphatidylglycerol and cardiolipin) among the inner and the outer leaflet. In principle, this holds true for most bacteria, except for those living at extremely high temperatures. For further information, see also Chapter 1 of this volume. 

In bacteria, phosphatidylserine is formed by the condensation of serine with CDP-diacylglycerol decarboxylation of phosphatidylserine produces phosphatidylethanolamine. Phosphatidylglycerol is formed by condensation of CDP-diacylglycerol with glycerol 3-phosphate, followed by removal of the phosphate in monoester linkage. 

In E. coli, Phospholipid Synthesis Generates Phosphatidylethanolamine, Phosphatidylglycerol, and Diphosphatidylglycerol... 

Phospholipase A1 pldA Outer membrane Phosphatidylethanolamine, phosphatidylglycerol, cardiolipin, and lyso derivatives... 

See also Molecular Structures and Properties of Lipids, Phosphatidic Acid, Cardiolipin, Phosphatidylserine, Phosphatidylethanolamine, Phosphatidylglycerol, Phosphatidylcholine, CDP-Diacylglycerol, Phosphatidylglycerol-3-Phosphate, Phosphatidylinositol, Lung Surfactant, Sphingolipids, Glycosphingolipids,... 

Figure 4.9 Representative ESI-MS analysis of lipid classes resolved by intrasource separation. Lipid extracts from mouse liver samples were prepared by using a modified procedure of Bligh and Dyer [1]. MS analysis was performed with a TSQ Vantage triple-quadrupole mass spectrometer (Thermo Fisher Scientific, San Jose, CA) equipped with an automated nanospray apparatus (i.e., TriVersa, Advion Bioscience Ltd., Ithaca, NY) and Xcalibur system software. Mass spectra were acqnired directly from the diluted hpid extract in the negative-ion mode (a), after addition of 50 nmol LiOH/mg of protein in the diluted lipid extract and analyzed in the negative-ion mode (h), or the identical hpid solution to that in (b) in the positive-ion mode (c). IS denotes internal standard PC, PE, PG, PI, PS, TAG, NEFA, and CL stand for phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidyUnositoL phosphatidylserine, triacylglycerol, nonesterified fatty acid, and doubly charged cardioUpin, respectively.

Dembitsky and coworkers 164-169) found phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylser-ine in Pseudevernia furfuracea and other lichens. 

B, phosphatidylethanolamine C, phosphatidylglycerol D, diphosphatidylglycerol (cardiolipin). Ra.COO and Rb.COO are fatty acid residues. 

Today s mitochondria lack most of the genes involved in phosphohpid metabolism. Therefore, mitochondria have to import most of their hpids. Phospholipids such as phosphatidylcholine, phosphatidylserine, phosphatidylglycerol, and phosphatidylinositol must be synthesized in the endoplasmatic reticulum under the control of nuclear genes and then transferred to mitochondria (Voelker, 2000) (Figure 1). Mitochondria use both nuclear and mitochondrial encoded proteins to further diversify phospholipids (Dowhan, 1997 Kent, 1995 Daum, 1985). Thus, a nuclear phosphatidylserine decarboxylase converts phosphatidylserine into phosphatidylethanolamine, or mitochondrial encoded cardiolipin synthase converts phosphatidylglycerol into cardiolipin which is incorporated exclusively into the inner mitochondrial membrane. 

Figure 1. Control of mitochondrial biogenesis by the nuclear genome. Most mitochondrial proteins, including cytochrome c, are nuclear gene products which are subsequently imported into mitochondria. Similarly, most enzymes involved in synthesis of mitochondrial phosphoplipids are encoded in the nuclear genome. Being located in the endoplasmatic reticulum, they synthesize phosphatidylcholine (PtdCho), phosphatidylserine (PtdSer), phosphatidylglycerol (PG) and phosphatidylinositol (Ptdins). The phospholipids are transferred to the outer membrane. The imported lipids then move into the inner membrane at contact sites. Mitochondria then diversify phospholipids. They decarboxylate phosphatidylserine to phosphatidylethanolamine (PtdEtN), but the main reaction is the conversion of imported phosphatidylglycerol to cardiolipin (CL). Cardiolipins localize mainly in the outer leaflet of the inner membrane.

Phosphatidylserine and phosphatidylglycerol can serve as precursors of other membrane lipids in bacteria (Fig. 21-25). Decarboxylation of the serine moiety in phosphatidylserine, catalyzed by phosphatidylserine decarboxylase, yields phosphatidylethanolamine. In E. coli, condensation of two molecules of phosphatidylglycerol, with elimination of one glycerol, yields... 

Yeast pathways for the synthesis of phosphatidylserine, phosphatidylethanolamine, and phosphatidylglycerol are similar to those in bacteria phosphatidylcholine is formed by methylation of phosphatidylethanolamine. 

Five kinds of phospholipid predominate phosphatidylcholine, phosphatidylethanolamine, phosphatidyl-serine, phosphatidylglycerols, and sphingomyelin. Usually there are also small amounts of phosphatidyli-nositol. The major phospholipid in animal cells is phosphatidylcholine, but in bacteria it is phosphatidylethanolamine. The phospholipids of E. coli consist of 80% phosphatidylethanolamine, 15% phosphati-dylglycerol, and 5% diphosphatidylglycerol (cardio-lipin). Significant amounts of cardiolipin are found only in bacteria and in the inner membrane of mitochondria. Sphingomyelin is almost absent from mitochondria, endoplasmic reticulum, or nuclear membranes. 

Figure 21-3 Major pathways of synthesis of fatty acids and glycerolipids in the green plant Arabidopsis. The major site of fatty acid synthesis is chloroplasts. Most is exported to the cytosol as oleic acid (18 1). After conversion to its coenzyme A derivative it is converted to phosphatidic acid (PA), diacylglycerol (DAG), and the phospholipids phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE). Desaturation also occurs, and some linoleic and linolenic acids are returned to the chloroplasts. See text also. From Sommerville and Browse.106 See also Figs. 21-4 and 21-5. Other abbreviations monogalactosyldiacylglycerol (MGD), digalactosyldiacylglycerol (DGD), sulfolipid (SL), glycerol 3-phosphate (G3P), lysophosphatidic acid (LPA), acyl carrier protein (ACP), cytidine diphosphate-DAG (CDP-DAG).

Glycerophospholipids contain a glycerol skeleton to which two fatty acids are esterified saturated fatty acids occupy mostly sn-position 1, whereas unsaturated fatty acids are mainly present on sn-position 2. The third hydroxyl is linked to a phosphate group to which an organic base is mostly esterified (Fig. 1). The most important components of soybean lecithin are phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). Phosphatidic acid (PA) may become important due to the presence of phospholipase D this enzyme slowly converts PC into PA in vegetable lecithins. Phosphatidylserine (PS), phosphatidylglycerol (PG), and lyso-phosphatidylcholine (LPC) are known as minor components lysophospholipids contain only one acyl group per molecule. Besides, ether phospholipids occur in which one or both fatty acyl... 

Escherichia coli contains three important classes of phospholipids phosphatidylethanolamine (75%-85%), phosphatidylglycerol (10%-20%), and diphosphatidylglycerol (5%-15%). All three of these phospholipids share the same biosynthetic pathway up to the formation of CDP-diacyl-glycerol (fig. 19.2), after which the pathways branch (fig. 19.3). 

The final reactions for the biosynthesis of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol all occur on the cytosolic surface of the endoplasmic reticulum and Golgi apparatus (fig. 19.9). By contrast, phosphatidylglycerol and diphosphatidylglycerol are synthesized on the mitochondrial membrane where they remain for the most part. 

Fig. B.4.1. Schematic representation of membrane phospholipids such as phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylglycerol, and phosphatidylinositol.

Bilayer composition can be almost infinitely varied by choice of the constituent lipids. Phosphatidylcholine (PC), a neutral phospholipid, has emerged as the major lipid component used in the preparation of pharmaceutical liposomes. Phosphatidylglycerol and phosphatidylethanolamine are also widely used. Liposomal bilayers may also accommodate sterols, glycolipids, organic acids and bases, hydrophilic polymers, antibodies and other agents, depending on the type of vesicle required. 

Phosphodiesterase (Hydrolysis) Activity. A rather broad substrate specificity is exhibited by the purified phospholipase D (phosphodiesterase activity). It can attack phosphatidylcholine, phosphatidylethanolamine, phospha-tidylserine, and phosphatidylglycerol. In most cases, Ca2+ was an activator, but variable results were obtained on the positive influence of diethyl ether on the catalytic activity of different sources of this enzyme. Usually the optimum pH was in the range from 5.0 to 7.0. Mammalian phospholipase D, containing both the phosphodiesterase and transphosphatidylase activities, exhibited a broad-range substrate specificity similar to that of the plant enzyme. However, the mammalian enzyme showed a dependency for the presence of oleic acid in the reaction system (Kobayashi and Kanfer, 1991). 

Figure 9.26 Asymmetry of phospholipids in the human erythrocyte and B. megaterium plasma membranes. "Total lipid" indicates 50% of lipid on each of the two sides of the bilayer. SM, PC, PE, PS, and PG are sphingomyelin, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylglycerol, respectively. (Reproduced by permission from Vance DE, Vance JE. Biochemistry of Lipids and Membranes. Menlo Park Benjamin/Cummings, 1985, p. 477.)...

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