Human Biochemistry, Volume 1 - Murray R. 1993

Bioenergetics and Metabolism of Carbohydrates and Lipids
Metabolism of Acylglycerols and Sphingolipids
Sphingolipid Metabolism

Phosphosphingolipids (Sphingomyelins)

Sphingomyelins are Phospholipids that contain a fatty acid, a phosphate group, Choline, and a complex amino alcohol known as sphingosine. Sphingomyelins do not contain glycerol.

Sphingosine (Fig. 25.6) is synthesized in The Endoplasmic reticulum. Following activation via interaction with Pyridoxal phosphate, The amino acid Serine reacts with palmitoyl-CoA to yield 3-ketosphinganine with the release of CO₂. Sphingosine is formed through two oxidation-reduction reactions: the first utilizes NADPH as a hydrogen donor, while the second is catalyzed by a flavoprotein-containing enzyme similar to the acyl-CoA dehydrogenase involved in ß-Oxidation.

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Fig. 25.6. Biosynthesis of sphingosine. FP — flavoprotein.

Fig. 25.7. Biosynthesis of ceramide and sphingomyelin.

Ceramide (N-acylsphingosine) serves as an intermediate in The biosynthesis of sphingomyelin and is produced through the interaction of sphingosine with acyl-CoA (Fig. 25.7). The acyl group is typically a long-chain saturated or monoenoic fatty acid. Sphingomyelin is generated by the reaction of ceramide with CDP-choline or phosphatidylcholine. In the latter case, the reaction is analogous to one of the pathways in phosphatidylcholine biosynthesis (Fig. 25.1).