Sphinganine, acylation

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. 

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. 

When the amino group of sphingosine or sphinganine is acylated with a fatty acid, the product... 

The synthesis of the ceramide lipid moiety of GSLs is initiated in the endoplasmic reticulum (ER) (6) via the condensation of serine and palmitoylCoA. This enzyme has been cloned (7). The product is 3-keto-sphinganine that then is reduced to sphinga-nine and acylated by ceramide synthase with a long-chain fatty acid to form dihydroceramide, which is converted to ceramide by ceramide desaturase, which inserts the 4,5-trans double bond. 

Sphingolipid biosynthesis is catalyzed by membrane-bound enzymes of the endoplasmic reticulum. Sphingo-sine, an acylaminoalcohol, is synthesized from palmitoyl-CoA and serine in a reaction that requires pyridoxal phosphate, NADPH, and Mn + (Figure 19-7). The exact pathway of ceramide synthesis is not known. The acyl group may be added to the 2-amino group of sphinganine,... 

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