Comparison of de novo sphingolipid biosynthesis in LY-B and LY-B/cLCB1 cells. LY-B and LY-B/cLCB1 cells were incubated with 0.1 mM [13C]-palmitic acid for 0, 3 and 6 h and the sphingolipids labeled in the sphingoid base alone (BASE) plus the sphingoid base and fatty acid (DUAL) were measured by LC ESI-MS/MS. The black bars represent the sphingolipids in LY-B/cLCB1 cells while the white bars indicate the LY-B cells. (A) [13C]-labeled long-chain bases (LCB) sphingosine, So; sphinganine, Sa; sphingosine 1-phosphate, SoP; and sphinganine 1-phosphate, SaP. (B-D) provide the sum of the label in the BASE and DUAL subspecies of ceramide, Cer, monohexosylceramides, HexCer, and sphingomyelins, SM, based on variation in the chain length of the amide-linked fatty acid (shown by chain length:number of double bonds).