Sphinganines

Sphingolipids are biosynthesized by adding head groups to the ceramide moiety. Sphinganine, also termed dihy-drosphingosine, is biosynthesized by a decarboxylating condensation of serine with palmitoyl-CoA to form a keto intermediate, which is then reduced by NADPH (Fig. 3-9). 

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 11.24 A summary of the reactions involved in synthesis of sphingomyelin. Reaction between serine and palmitoyl-CoA produces 3-oxosphinganine, which is converted to sphingamine. Attachment of a Long-chain fatty acid to the amino group of sphinganine produces dihydroxyceramide. Ceramide reacts with phosphatidylcholine the phosphocholine component forms an ester bond with the hydroxyl group at position one of ceramide.

This enzyme [EC 1.1.1.102] catalyzes the reversible reaction of sphinganine with NADP+ to produce 3-dehydro-sphinganine and NADPH. 

Compounds similar to glycerol, called sphingoids, are derivatives of sphinganine (o-erj t/iro-2-aminooctadecane-l,3-diol). The trivial name sphinganine implies the stereochemistry the use of the stereodescriptor D-erythro in the systematic name is to be noted. 

Add to each tube 5 pi internal standard (25 pM D-erythro-C20-sphinganine). 

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. 

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

In contrast to the striking divergences in the carbohydrate parts, respective ceramide moieties resemble those of other cestode glycosphingolipids in so far as sphinganine (d18 0) and 4-hydroxy-sphingoid bases (tl 8 0, t20 0) as well as, in part hydroxylated, fatty acids with 16 to 28 carbon atoms, in particular C26 0 and C28 0, represent predominant ceramide constituents, which might be an indication of similar biosynthetic routes. 

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