Ceramides head group addition

Fig. 8. Head-group additions to ceramide in a schematic representation. Starting with a given molecular subspecies of ceramide (Fig. 7), head groups can be added to make sphingomyelin by addition of a phospho-choline moiety (by transesterification from phosphatidylcholine), phosphate (from ATP), glucose (from UDP-Glc), galactose (from UDP-Gal), or a fatty acid (by transacylation from phosphatidylcholine or phosphatidylethanolamine). Subsequent metabolites are formed by sequential carbohydrate addition (from UDP-sugars except for GDP-fucose, GDP-mannose and CMP-sialic acid) or addition of sulfate.

FIGURE 21-31 Biosynthesis of sphingolipids. Condensation of palmitoyl-CoA and serine followed by reduction with NADPH yields sphinganine, which is then acylated to N-acylsphinganine (a ceramide). In animals, a double bond (shaded pink) is created by a mixed-function oxidase, before the final addition of a head group phosphatidylcholine, to form sphingomyelin glucose, to form a cerebroside. 

Head groups of ceramides contain multiple hydroxyl groups with a well-defined stereochemistry, so that stereospecific interactions between ceramides and enantiomers of a chiral drug may cause enantioselective permeation. In addition, differential binding of enantiomers of chiral drugs... 

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