Glycerophospholipids phosphatidylglycerol

FIGURE 8.6 Structures of several glycerophospholipids and space-filling models of phosphatidylcholine, phosphatidylglycerol, and phosphatidylinositol. 

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 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-... 

FIGURE 21-26 Synthesis of cardiolipin and phosphatidylinositol in eukaryotes. These glycerophospholipids are synthesized using strategy 1 in Figure 21-24. Phosphatidylglycerol is synthesized as in bacteria (see Fig. 21-25). PI represents phosphatidylinositol. 

Cardiolipin is a glycerophospholipid made by combining two molecules of phosphatidylglycerol and splitting out one of the glycerol molecules (Figure 19.4). Cardiolipin is present in heart muscle membranes and in the membranes of spirochetes, such as the organism that causes syphilis. 

See also Glycerophospholipid Pathway, Glycerophospholipids, Glycerol, Phosphatidylglycerol. Initiation of DNA Replication... 

See also Glycerophospholipid Pathway, Phosphatidylglycerol-3-Phosphate, Glycerophospholipid Biosynthesis in Bacteria, Glycerophospholipids, Glycerophospholipid Pathway,... 

On the other hand, glycerophospholipids are usually the major constituents of bacterial membranes. These lipids are usually enriched with saturated fatty acids at the sn-l position and with unsaturated acids at the sn-2 position. In cyanobacteria, the distribution is governed by chain length rather than unsaturation with sn-l-Cis and sn-2-Cte being the rule (Zepke et al., 1978). The cyanobacteria are also exceptional in that they synthesize (and accumulate) only one phospholipid, phosphatidylglycerol. 

The unique R1/R2 (saturated/imsaturated) acyl chains combination is a key feature that you should keep in mind when studying membrane structure and function (see Chapter 2). Apart from PC, PE, and PS, a few other glycerophospholipids are biologically important and their structures can be easily deduced from the condensation of PA with an organic alcohol (e.g., glycerol or inositol) phosphatidylglycerol (PC), which is present in mitochondrial membranes, and phosphatidylinositol (PI), a minor component of plasma membrane that plays a key role in signal transduction (see Chapter 3). 

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]. 

---