Phosphatidylethanolamine phosphatidylserine

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... 

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.

Glycolipids, gangliosides, phosphatidylinositol Phosphatidylethanolamine Phosphatidylserine Phosphatidylcholine, sphingomyelin Lysolecithin... 

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.)...

Lecithin, an edible by-product of oil processing possessing a variety of useful functionalities, is primarily a mixture of phospholipids such as phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, and phospha-tidic acid and contains minor quantities of other water-soluble or hydratable components such as glycolipids and oligosaccharides (78). The degumming of oil with... 

Liver cells (Cholesterol Phosphatidylcholine Phosphatidylethanolamine Phosphatidylserine SrhinKomvelioe 50% 50%... 

The outer layer of the membrane is made up of phosphatidylcholine whereas the inner layer is made up of phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol. 

A characteristic of all membranes is an asymmetry in lipid composition across the bilayer. Although most phospholipids are present in both membrane leaflets, they are commonly more abundant in one or the other leaflet. For instance, in plasma membranes from human erythrocytes and certain canine kidney cells grown in culture, almost all the sphingomyelin and phosphatidylcholine, both of which form less fluid bilayers, are found in the exoplasmic leaflet. In contrast, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol, which form more fluid bilayers, are preferentially located in the cytosolic leaflet. This segregation of lipids across the bilayer may influence membrane curvature (see Figure 5-8c). Unlike phospholipids, cholesterol is relatively evenly distributed in both leaflets of cellular membranes. 

In addition to phosphatidylcholine, smaller amounts of other phospholipids such as phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, and sphingomyelin... 

Erythrocytes Cholesterol Phosphatidylcholine Phosphatidylethanolamine Phosphatidylserine Phosphatidyl nositol Sphingomyeline 40% 00%... 

Phosphatidylcholine Phosphatidylethanolamine Phosphatidylserine Phosphatidylinositol bisphosphate (PIP2) Phosphatidylglycerol Cardiolipin... 

Phosphatidylcholine Phosphatidylethanolamine Phosphatidylserine Phosphatidylinositol Phosphatidic acid... 

Figure 35.11 Phosphatidic acid. This is the parent molecule of the phospholipids. Like triacylglycerol, it has a glycerol backbone but instead comprises two fatty acyl groups and one phosphate group. When this phosphate reacts with OH groups of compounds such as choline, ethanolamine, serine or inositol, phospholipids are formed known as phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol (Chapter 36).

Phospholipids can form salts, for example with metal ions, due to the presence of one free hydroxyl group of the bound phosphoric acid in phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol and two free hydroxyl groups in phosphatidic acid. Mostly, calcium and magnesium ions are involved in these reactions, but the resulting complexes have hydrophobic character, as in metal soaps. Cations of heavy metals (copper, manganese and iron) bound in phospholipids catalyse autoxidation significantly less than free metal ions, phospholipids can thus become synergists of antioxidants. 

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