Ceramide sphingolipids from

Figure 6-15. Synthesis of sphingolipids. NANA = W-acetylneuraminic acid G/c = glucose Gal = galactose GalNAc = N-acetylgalactosamine PIP = pyridoxal phosphate FA = fatty acyl groups derived from fatty acids = hydrophobic chains of ceramide. The dashed box contains the portion of ceramide derived from serine.

Fig. 33.33. S5mthesis of sphingolipids from ceramide. PhosphochoUne or sugars add to the hydroxymethyl group of ceramide (in blue) to form sphingomyelins, cerebrosides, sulfatides, globosides, and ganghosides. Gal = galactose Glc = gucose GalNAc = iV-acetylgalac-tosamine NANA = A-acetylneuraminic acid.

Ceramide types III and IV were isolated from stratum comeum lipid extracts and separated from cholesterol, free fatty acids, and triglycerides on a silica column (ELSD) in <15min using a 19/1 hexane/ethanol mobile phase [717]. Related compound classes (hydroxy fatty acid ceramide, C2 ceramide, sphingolipid, phyto-sphingosine) were separated on a silica column using a 90/10/1/1 chloroform/ ethanol/triethylamine/formic acid mobile phase. In this case elution was complete in 10 min. 

Because membranes components participate in nearly every cell activity their structures are also dynamic and far from the equilibrium states that are most readily understood in biophysical terms. Newly synthesized bilayer lipids are initially associated with endoplasmic reticulum (Ch.3) whereas phospholipids initially insert into the cytoplasmic leaflet while cholesterol and sphingolipids insert into the luminal endoplasmic reticulum (ER) leaflet. Glycosylation of ceramides occurs as they transit the Golgi compartments, forming cerebrosides and gangliosides in the luminal leaflet. Thus, unlike model systems, the leaflets of ER membranes are asymmetric by virtue of their mode of biosynthesis. 

Sphinganine is acylated, then dehydrogenated to form ceramide. Free sphingosine, also termed sphingenine, salvaged from sphingolipid breakdown can be enzymatically acylated with acyl-CoA to form ceramide. 

Gatt, S., 1963, Enzymatic hydrolysis of sphingolipids. 1. Hydrolysis and synthesis of ceramides by an enzyme from rat brain. J. Biol. Chem. 238 3131-3133. 

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