Glycerophospholipids phosphatidylinositol

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

There are few commercial fungicides that have glycerophospholipid biosynthesis inhibition as their mode of action. The validated targets are phosphatidylcholine synthesis and phosphatidylinositol synthesis. 

FIGURE 10-15 The specificities of phospholipases. Phospholipases Ai and A2 hydrolyze the ester bonds of intact glycerophospholipids at C-l and C-2 of glycerol, respectively. Phospholipases C and D each split one of the phosphodiester bonds in the head group. Some phospholipases act on only one type of glycerophospholipid, such as phosphatidylinositol 4,5-bisphosphate (shown here) or phosphatidylcholine others are less specific. When one of the fatty acids has been removed by a type A phospholipase, the second fatty acid is cleaved from the molecule by a lysophospholipase (not shown). 

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 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. 

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. 

Phosphatidylinositol is a glycerophospholipid that can be made by the reaction shown below ... 

Phosphatidylinositol is uncommon in bacteria and is found in a few Gram-positive species only. In actinomycetes and a few other bacteria mannosides of phosphatidylinositol may be present. Other glycerophospholipids such as phosphatidic acid and phosphatidylserine have a widespread occurrence in bacteria but only in small amounts. Both of these lipids play an important role as metabolic intermediates (Finnerty, 1978 Raetz, 1978). 

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). 

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