Question

Write out the mechanisms (reactant, product structures and electron movement) for each synthetic step to the final product for the synthesis of sphingomyelin.

Answer 1

1. The initiation of the synthesis of the sphingoid bases (sphingosine, dihydrosphingosine, and the various ceramides) takes place via the condensation of palmitoyl-CoA and serine.

This reaction occurs on the cytoplasmic face of the endoplasmic reticulum (ER) and is catalyzed by the pyridoxal phosphate-dependent enzyme, serine palmitoyltransferase (SPT).

2. The product of this reaction is 3-ketosphinganine (3-ketodihydrosphingosine).

SPT is the rate-limiting enzyme of the sphingolipid biosynthesis pathway.