Sphingomyelin structure

The major fatty acids of GD3 and GM3 (the major gangliosides of bovine milk) are 22 0, 23 0, 24 0 and 16 0, with both species of ganglioside having similar fatty acid compositions (Table 1.14). These fatty acids are also a feature of the sphingomyelin structure. Martin et al. (2001), who... 

FIGURE 8.12 A structure and a space-filling model of a choline sphingomyelin formed from stearic acid. 

Sphingomyelin, 1066-1067 Sphingosine, structure of, 1067 Spin density surface, allylic radical, 342... 

Triacylglycerols are the major energy-storing lipids, whereas phosphoglycerols, sphingomyelin, and gly-cosphingolipids are amphipathic and have structural functions in cell membranes as well as other specialized roles. 

FIGURE 9.7 Structure of S-O-acyl-D-er t/iro-sphingomyelin. (From Kramer, J. et al., Bio-chim. Biophys. Acta, 1303, 47-55, 1996. With permission.)... 

Figure I. Displayed are the structures of sphingomyelin and ceramide. Sphingomyelinases function as phospholipases C to hydrolyze sphingomyelin.

The illustration shows a model of a small section of a membrane. The phospholipids are the most important group of membrane lipids. They include phosphatidylcholine (lecithin), phosphatidylethanolamine, phos-phatidylserine, phosphatidylinositol, and sphingomyelin (for their structures, see p. 50). in addition, membranes in animal cells also contain cholesterol (with the exception of inner mitochondrial membranes). Clycoli-pids (a ganglioside is shown here) are mainly found on the outside of the plasma membrane. Together with the glycoproteins, they form the exterior coating of the cell (the gly-cocalyx). 

Apo A-I is the main structural apolipoprotein on HDL particles it is synthesized in hepatic and enteric cells. Bound phosphatidylcholine and sphingomyelin participate in the creation of protein-phospholipid complexes. 

Cholesterol is an important structural component of cellular membranes, where it plays a role in modulating membrane fluidity and phase transitions, and, together with sphingomyelin, forms lipid rafts or caveolae, which are sites where proteins involved in diverse signaling pathways become concentrated. Furthermore, cholesterol is a precursor of oxysterols, steroid hormones, and bile acids. 

FIGURE 10-13 The similarities in shape and in molecular structure of phosphatidylcholine (a glycerophospholipid) and sphingomyelin (a sphingolipid) are clear when their space-filling and structural formulas are drawn as here. 

Hydrophobic and Hydrophilic Components of Membrane Lipids A common structural feature of membrane lipids is their amphipathic nature. For example, in phosphatidylcholine, the two fatty acid chains are hydrophobic and the phosphocholine head group is hydrophilic. For each of the following membrane lipids, name the components that serve as the hydrophobic and hydrophilic units (a) phos-phatidylethanolamine (b) sphingomyelin (c) galactosyl-cerebroside (d) ganglioside (e) cholesterol. 

Structure of sphingomyelin, showing sphinganine (in green box) and ceramide components (in dashed box). 

Structural components and function of sphingomyelin The alcohol sphingosine attached to a long-chain fatty acid produces a ceramide. Addition of a phosphorylcholine produces the phospholipid sphingomyelin, which is the only significant sphingophospholipid in humans. It is an important constituent of myelin. 

In addition to phosphoglycerides, membranes from animal cells usually contain a second group of phospholipids, the sphingolipids. Sphingomyelin, which is representative of this group, has the structure... 

McIntosh, T.J., Simon, S.A., Needham, D., and Huang, C.H. 1992. Structure and cohesive properties of sphingomyelin/cholesterol bilayers. Biochemistry (Mosc.) 31, 2012-2020. 

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