In this article we will discuss about the metabolism of sphingolipids, explained with the help of a suitable diagram.
Sphingosine results from the condensation of palmityl-coenzyme A with serine. The next step consists in the binding of a fatty acid which gives a ceramide. This ceramide can react either with CDP-choline to form a sphingomyelin, or with UDP-galactose to give a cerebroside, or with other UDP- monosaccharides to yield the other sphingoglycolipids (the monosaccharides are transferred one after the other by a specific enzyme).
The sialic acid of gangliosides is transferred by reaction of a glycolipid with CMP-sialic acid (CMP-NeuAc). These reactions are diagrammatically represented in figure 5-25. The catabolism of these compounds takes place by reverse reactions catalyzed by specific osidases at each step.
The glycosyltransferases and glycosidases involved in this metabolism are different from those involved in the metabolism of glycoproteins. In the case of glycolipids, the substrates being insoluble in aqueous medium, the enzymes require protein activators in order to act.
Let us note that the synthesis and catabolism of glycosyldiglycerides take place according to a similar diagram, the primary acceptor being a diglyceride and not a ceramide.