Figure 2.

Schematic outline of the ceramide/sphingosine-1-phosphate rheostat. Single arrows indicate irreversible processes, i.e. no enzymatic activities have been detected that reverses the metabolic pathway depicted by the arrows. Of particular interest is the degradation of sphingosine-1-phosphate to hexadcanal and phophoethanolamine which is a sink for sphingosine-1-phosphate irreversibly terminating its signalling activity.