(A) The scheme depicts the intracellular oxidation of dihydro-ceramidoid C12-dhCCPS to the corresponding ceramidoid C12-CCPS by the enzyme dihydroceramide desaturase (B) SMS-KCNR and MCF-7 cells were treated with 0.5 μM C12-dhCCPS for 15 min, 2 h, 6 h and 24 h. Cells were harvested at these time points, and pyridinium conjugated ceramidoids (Pyr-Cers) were measured by LC/MS as described in the “Experimental Procedures.” The percentage of the total detected Pyr-Cers that was converted to C12-dhCCPS are depicted here. The data presented are representative of the mean of at least three independent experiments ± S.D. The error bars represent the standard deviations, and when not seen, they are smaller than the thickness of the lines on the graphs.