Biochemistry - The Chemical Reactions of Living Cells, Volume 2 - D. Metzler 1980

Biosynthesis: how new molecules are formed
Metabolism of triglycerides, phospholipids, and glycolipids
Sphingolipids

Sphingolipids include phospho- and Glycolipids, which are derivatives of sphingosine and other long-chain bases. To date, at least 60 compounds of this type have been identified [70]. Their molecules consist of a carbon chain containing 14–22 carbon atoms and, occasionally, 1–2 double bonds. Both iso- and anteiso-series compounds are found among sphingolipids. Sphingosine is a C₁₈ compound formed by the Condensation of palmityl-CoA with Serine [Equation (12-24)]. During the condensation reaction, Carbon dioxide is cleaved from serine [Equation (12-24), reaction a; Chapter 8, Section D, 3, c], and the resulting ketone is reduced with the participation of NADPH [Equation (12-24), reaction b] to sphinganine, a widespread component of animal sphingolipids. Sphinganine is oxidized by a flavoprotein to sphingosine [Equation (12-24), reaction c] or hydroxylated to form phytosphingosine [Equation (12-24), reaction d]. The pathways for The conversion of sphingosine bases into sphingomyelins and cerebrosides are summarized in Fig. 12-5. The breakdown of sphingosine in Cells is presumed to proceed via chain Cleavage to palmitaldehyde through a PLP-mediated process [71]. While the pathways of complex lipid synthesis have been studied in considerable detail, very little is known about the dynamics of synthesis and turnover of the membranes formed from them.

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Of particular interest is the established fact of phospholipid transfer from one Membrane Structure to another. For example, isolated Cell/35.html">Mitochondria and microsomes are capable of exchanging phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol. It has been shown that The transfer of phosphatidylcholine is catalyzed by a specific exchange protein [72] [Equation (12-24)].