Glycerophospholipids, also known as phosphoglycerides, are a major class of phospholipids and the primary lipids found in membranes. These lipids all contain or are derived from phosphatidic acid (PA), which is a form of DAG with a phosphate group on carbon 3. PA serves as the simplest phosphoglyceride and acts as the precursor for other members within this category.

One method of synthesizing glycerophospholipids involves esterifying the phosphate group on PA with a compound containing an alcohol group. For example, two molecules of PA can be esterified through their phosphate groups to an additional molecule of glycerol, resulting in the formation of cardiolipin or diphosphatidylglycerol. Cardiolipin is present in both bacterial and eukaryotic membranes. In eukaryotes, it is primarily found in the inner mitochondrial membrane, where it plays a crucial role in maintaining the structure and function of specific respiratory complexes within the electron transport chain. It is important to note that cardiolipin is antigenic and can be recognized by antibodies.

Another type of glycerophospholipid is the plasmalogen, which is formed when the fatty acid at carbon 1 of a glycerophospholipid is replaced by an unsaturated alkyl group attached to the core glycerol molecule via an ether linkage. An example of a plasmalogen is phosphatidylethanolamine, which is abundant in nerve tissue. It shares structural similarities with the antibody raised against Treponema pallidum, the bacterium responsible for causing syphilis. The Wasserman test for syphilis detects the presence of these antibodies. Additionally, plasmalogen phosphatidylcholine, abundant in heart muscle, is another quantitatively significant ether lipid found in mammals. It is worth noting that the names of plasmalogens contain "al" instead of "yl."

Platelet-activating factor (PAF) is an example of another ether glycerophospholipid. PAF contains a saturated alkyl group attached to carbon 1 via an ether link and an acetyl residue at carbon 2 of the glycerol backbone. PAF is synthesized and released by various cell types and binds to surface receptors, triggering potent thrombotic and acute inflammatory events. It activates inflammatory cells, mediates hypersensitivity, acute inflammatory, and anaphylactic reactions. PAF also causes platelet aggregation and activation, stimulates neutrophils and alveolar macrophages to produce superoxide radicals for bacterial killing, and lowers blood pressure. Notably, PAF is one of the most potent bioactive molecules known, exerting its effects at extremely low concentrations of 10^-11 mol/l.

Moving on to another class of phospholipids, sphingomyelin falls under the category of sphingophospholipids.
Phospholipids that contain glycerol are called glycerophospholipids (or phosphoglycerides). Glycerophospholipids constitute the major class of phospholipids and are the predominant lipids in membranes. All contain (or are derivatives of) phosphatidic acid (PA), which is DAG with a phosphate group on carbon 3 (Fig. 17.1B). PA is the simplest phosphoglyceride and is the precursor of the other members of this group.
1.
From phosphatidic acid and an alcohol: The phosphate group on PA can be esterified to a compound containing an alcohol group (see Fig. 17.1). For example: 2.
Cardiolipin: Two molecules of PA esterified through their phosphate groups to an additional molecule of glycerol form cardiolipin, or diphosphatidylglycerol (Fig. 17.2). Cardiolipin is found in membranes in bacteria and eukaryotes. In eukaryotes, cardiolipin is virtually exclusive to the inner mitochondrial membrane, where it maintains the structure and function of certain respiratory complexes of the electron transport chain. [Note: Cardiolipin is antigenic and is recognized by antibodies 3.
Plasmalogens: When the FA at carbon 1 of a glycerophospholipid is replaced by an unsaturated alkyl group attached by an ether (rather than by an ester) linkage to the core glycerol molecule, an ether phosphoglyceride known as a plasmalogen is produced. For example, phosphatidalethanolamine, which is abundant in nerve tissue (Fig. 17.3A), is the plasmalogen that is similar in structure to (Ab) raised against Treponema pallidum, the bacterium that causes syphilis. The Wasserman test for syphilis detects these Ab.] phosphatidylethanolamine. Phosphatidalcholine (abundant in heart muscle) is the other quantitatively significant ether lipid in mammals. [Note: Plasmalogens have “al” rather than “yl” in their names.] plasmalogen phosphatidalethanolamine. B. Platelet-activating factor. ( is a long, hydrophobic hydrocarbon chain.) 4. Platelet-activating factor: A second example of an ether glycerophospholipid is platelet-activating factor (PAF), which has a saturated alkyl group in an ether link to carbon 1 and an acetyl residue (rather than a FA) at carbon 2 of the glycerol backbone (Fig. 17.3B). PAF is synthesized and released by a variety of cell types. It binds to surface receptors, triggering potent thrombotic and acute inflammatory events. For example, PAF activates inflammatory cells and mediates hypersensitivity, acute inflammatory, and anaphylactic reactions. It causes platelets to aggregate and activate and neutrophils and alveolar macrophages to generate superoxide radicals to kill bacteria (see p. 150). It also lowers blood pressure. [Note: PAF is one of the most potent bioactive molecules known, causing effects at concentrations as low as 10−11 mol/l.]
B. Sphingophospholipids: Sphingomyelin