Phosphatidylethanolamine glycerophospholipid

Our first issue with respect to the lipid bilayer is its composition. This varies from membrane to membrane but generally includes several glycerophospholipids— phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine—as well as... 

Glycerophospholipids differ in the structure of their head group common gycerophospholipids are phosphatidylethanolamine and phosphatidylcholine. The polar heads of the gycerophospholipids carry electric charges at pH near 7. 

The phospholipids in milk are synthesized by the mammary cell via pathways that are common to other mammalian cells. For further information on the synthesis of phospholipids in the mammary cell, see Kinsella and Infante (1978) and Patton and Jensen (1976). The major glycerophospholipids are phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine, and phosphatidylinositol. A more complete composition is given in Table 4.6, Patton and Jensen (1976). The acyl and alkyl compositions will be given later. In milk, the glycerophospholipids are found predominantly in the diacyl form. However, small... 

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... 

The positional distribution of fatty acids in phosphatidylcholine and phosphatidylethanolamine, the major glycerophospholipids, of bovine milk, were investigated by Morrison et al. (1965) and are shown in Table 1.13. Unlike triacylglycerols, phospholipids do not contain short-chain fatty acids (14 0 being the shortest chain fatty acid present at a significant level). This is probably due to differences in the route of synthesis, as most short-chain fatty acids are found at the sn-3 position of triacylglycerols, which in phospholipids is occupied by the phosphate moiety. In phospholipids, the polyunsaturated fatty acids tend to be esterified preferentially at the sn-2 position, while the saturated fatty acids show a preference for the sn-1 position (Table 1.13). For phosphatidylethanolamine, 18 2 and 18 3 are found predominantly at the sn-2 position, while 18 1 is fairly evenly distributed and 16 0 and 18 0 are predominantly at the sn-1 position. In phosphatidylcholine, which is more saturated than phosphatidylethanolamine, the distribution of saturated and unsaturated fatty acids is less distinct between... 

The structure of glycerophospholipids is characterized by a l,2-diacyl-3-phospho-5n-glycerol, or phosphatidyl moiety, and a variable headgroup linked to the phosphate. Major phosphoglycerides found in nature are phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylserine, phosphatidylinositol (PI), and diphospha-... 

The common diacyl glycerophospholipids also include phosphatidylethanolamine, phosphatidyl serine, and phosphatidylinositol. 

Phosphatidylethanolamine is a glycerophospholipid. Its biosynthetic reactions are shown in Figure 19.4 and here. 

The major glycerophospholipid of Gram-negative bacteria is phosphatidylethanolamine. It is also a major component of some Gram-positive species such as Bacillus. In contrast, phosphatidylcholine is seldom a major lipid in bacteria. In a few genera the ethanolamine head-group may be partly methylated (giving the mono- and dimethyl-derivatives). 

As shown in Figs 11.13 and 11.14, phos-phatidycholine (the major plant and animal glycerophospholipid) and phosphatidylethanolamine are both synthesized by a CDP-base pathway. This is the major route of their formation in both plants (Harwood, 1979 Moore, 1982) and animals (Bell and Coleman, 1980 Spanner, 1982). Three enzyme steps are required. Firstly, the base is phosphorylated by a kinase enzyme. Choline kinase (EC 2.7.1.32) and ethanolamine kinase (EC 2.7.1.82) are soluble enzymes and have been purified from several tissues. The activities may reside in the same protein (Ulane et al.y 1977) although separate enzymes have been purified from rat liver (Brophy and Vance, 1976) and soybean seeds (Wharfe and Harwood, 1979). 

The neutral glycerophospholipids, PC and phosphatidylethanolamine (PE), make up the bulk of the complex lipids derived from glycerophosphoric... 

Similarly, you can write the structures of phosphatidylethanolamine PE and phosphatidyl-serine PS (Fig. 1.16). Now you know how to write the structure of the three main membrane glycerophospholipids. At pH 7, both PC and PE are zwitterions (i.e., bear a positive and a negative charge). In contrast, PS has one positive and two negative charges, so that this lipid is globally anionic. ... 

FIGURE 3.23 Biosynthesis of anandamide. Phosphatidylethanolamine (PE) is condensed with an arachido-nate (C20 4ffl6) group given by a glycerophospholipid (not shown) in a reaction catalyzed by N-acyltransferase. This results in the synthesis of N-arachidonoyl PE, the precursor of anandamide. Then, this precursor is cleaved into anandamide and phosphatidic acid (PA) by N-acylphosphatidylethanolamine-hydrolyzing phospholipase D (NAPE-PLD). 

Anandamide is produced through Ca -stimulated hydrolysis of the phosphatidylethanolamine (PE) derivative N-arachidonoyl PE (Fig. 3.23). The N-arachidonoyl PE precursor is S5mthesized in the brain by an N-acyltransferase that catalyzes the transfer of an arachidonate group from a glycerophospholipid to the amino group of The second step of anan-... 

Phosphatidylethanolamine (PE) One of the most abrmdant glycerophospholipids, more abundant in the intracellular than in the extracellular leaflet of the plasma membrane. Formed by the addition of ethanolamine on a phosphatidic acid backbone. 

In 1987 Brozek et al., characterized an enzyme found in membranes of E. coli that catalyzes the transfer of a palmitate moiety from the sm-1 position of glycer-ophospholipids, such as phosphatidylethanolamine or phosphatidylglycerol, to the hydroxyl of the iV-linked acyl chain of lipid X [50], This enzyme is specific for glycerophospholipids as acyl donors. Acyl-ACP and acyl-CoA are not substrates [50]. The reaction is very specific for acyl chain length. No other fatty acyl chain can substitute for palmitate [50]. 

---