Phosphatidyl compounds membranes

Sphingomyelins are phosphorus-containing members of the second large class of membrane lipids known as sphingolipids (10.50b). The head group X is most commonly choline or ethanolamine, and these compounds resemble the corresponding phosphatidyl compounds (10.47) in their general... 

The other phospholipids can be derived from phosphatidates (residue = phosphatidyl). Their phosphate residues are esterified with the hydroxyl group of an amino alcohol choline, ethanolamine, or serine) or with the cyclohexane derivative myo-inositol. Phosphatidylcholine is shown here as an example of this type of compound. When two phosphatidyl residues are linked with one glycerol, the result is cardiolipin (not shown), a phospholipid that is characteristic of the inner mitochondrial membrane. Lysophospholipids arise from phospholipids by enzymatic cleavage of an acyl residue. The hemolytic effect of bee and snake venoms is due in part to this reaction. 

The anandamide precursor, phosphatidylethanol amine, is present in membranes almost always accompanied by phophatidylserine. It seemed reasonable to expect the formation of anandamide from its precursor will be paralleled by formation of N-arachidinoylserine from phosphatidyl serine. Indeed, A -arachidonoyl-L-serine (ARA-S) was found to be formed alongside anandamide (Fig. 4). This compound was isolated from bovine brain and its structure was elucidated by comparison with synthetic ARA-S. Contrary to anandamide, ARA-S binds very weakly to the known cannabinoid CBi and CB2 or vanilloid TRPVl receptors. However, it produces endothelium-dependent vasodilation of rat isolated mesenteric... 

Inositol-containing phospholipids of the plasma membrane are the starting compounds for formation of the signal substances diacylglycerol and inositol trisphophate. The plasma membrane contains the phospholipid phosphatidyl inositol, in which the phosphate group is esterified with a cychc alcohol, myo-D-inositol (Fig. 6.3). 

Fig. 6.9. A) Metabolism of phosphatidyl inositol lipids. The figure shows different membrane-associated phosphatidyl inositol phosphate compounds and their mutual conversion. PI3-kinase (PI3K) is responsible, in particular, for the formation of PtdIns(3,4,5)P3 from PtdIns(3,4)P2. For the reactions marked with a question mark, involvement of PI(3) kinase is not certain.

Arachidonic acid, a 20-carbon fatty acid, is the primary precursor of the prostaglandins and related compounds (see Figure 39.3). Arachidonic acid is present as a component of the phospholipids of cell membranes, primarily phosphatidyl inositol and other complex lipids.1 Free arachidonic acid is released from tissue phospholipids by the action of phospholipase A2 and other acyl hydrolases, via a process controlled by hormones and other stimuli (see Figure 39.3). There are two major pathways in the synthesis of the eicosanoids from arachidonic acid (see Figure 39.3). 

Phospholipids, or phosphoglycerides, are amphipathic compounds that are used to make cell membranes, generate second messengers, and store fatty acids for use in the generation of prostaglandins. They can be synthesized from phosphatidate, an intermediate in triglyceride synthesis. Two common phospholipids, phosphatidyl choline and phosphatidyl inositol, are shown below (4). 

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