title: Biosynthesis of long-chain (sphingoid) bases from serine by LM cells. Evidence for introduction of the 4-trans-double bond after de novo biosynthesis of N-acylsphinganine(s).
abstract: The de novo biosynthesis of sphinganine and sphingosine was studied using LM cells incubated with [14C] serine in serum-free media. Most of the radiolabeled long-chain bases were initially found in dihydroceramides (as sphinganine) and the proportion appearing in complex sphingolipids (as sphingosine) increased over time. Since free long-chain bases were not detected (although formation of 3-ketosphinganine, the first condensation product of serine and palmitoyl-CoA, could be demonstrated in vitro), it appears that the first step is rate-limiting for dihydroceramide biosynthesis. The kinetics suggested that after N-acyl-sphinganines were formed they were dehydrogenated to N-acylsphingosines. No evidence was found for the formation in vivo or in vitro of the putative intermediates of the direct biosynthesis of sphingosine from sphinganine (i.e. 3-ketosphingosine and free sphingosine). The conversion of N-acylsphinganines to N-acyl-sphingosines was confirmed by incubating cells with [14C] serine followed by unlabeled serine, which resulted in a rapid increase in the sphingosine-to-sphinganine ratio in amide-linked sphingolipids during the chase. These findings are most consistent with a pathway for long-chain base biosynthesis in which N-acyl-sphinganines are first synthesized by LM cells and the 4-trans-double bond is added to this or subsequent products, as opposed to the most cited pathway wherein sphingosine is made directly from sphinganine.
authors.forename: A H
authors.initials: AH
authors.lastname: Merrill
authors.forename: E
authors.initials: E
authors.lastname: Wang
mesh_terms: D000215:Acylation; D000818:Animals; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D051379:Mice; D012694:Serine / Q000378:metabolism*; D013107:Sphingolipids / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000378:metabolism
chemical_list: D002250:Carbon Radioisotopes; D013107:Sphingolipids; D012694:Serine; D013110:Sphingosine; C005682:safingol