BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 14. LIPID METABOLISM

14.7. Sphingolipid Metabolism

The Biosynthesis of Sphingolipids begins with the Synthesis of the aliphatic alcohol sphingosine. Serine and palmitoyl-CoA serve as precursors in its formation, reacting with each other to yield dihydrosphingosine. The latter, with the participation of the Coenzymes NADH and FAD, is first reduced at the carbonyl group, and then dehydrogenated in the aliphatic chain, thus converting into sphingosine. In subsequent biosynthetic reactions, the amino group of sphingosine is acylated to form ceramide, which is the primary intermediate metabolite in sphingolipid synthesis (Fig. 14.10).

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Fig. 14.10. Pathway of sphingolipid biosynthesis

Sphingomyelins are formed through the interaction of ceramide with CDP-Choline. Cerebrosides are produced by the attachment of a glycosyl residue from UDP-galactose or UDP-glucose. In the synthesis of the most complex sphingolipids, the gangliosides, Oligosaccharides containing one or more residues of N-acetylneuraminic or N-glycolylneuraminic acids (sialic acids) are attached to the glycosyl residue of the cerebroside.

The breakdown of sphingolipids during their METABOLISM involves lysosomal hydrolytic Enzymes, which hydrolyze lipid molecules into their constituent structural components.

The degradation of sphingomyelins also involves sphingomyelin phosphodiesterase, which cleaves sphingomyelin into molecules of phosphocholine and ceramide. The latter, in turn, is broken down by the action of ceramidase into sphingosine and a fatty acid: