Figure 2. Sphingolipids containing sphingosine are formed in the sur2Δ or sur2Δ scs7Δ yeast mutant strains expressing human DES1.

(a,b) The released sphingoid bases from strong alkaline hydrolysis-treated cells were converted into their DNP derivatives and analyzed by TLC (a) and HPLC (b) as described in Online Methods. For identification of lipids, the following standards were used: PHS, DHS, and sphingosine (S). (c) The lipids were extracted from cells, hydrolyzed by HCl, and separated by TLC with solvent system II. Sphingoid bases were visualized by spraying with 0.5% ninhydrin and heating at 100 °C. (d,e) Cells were labeled with [³H]DHS overnight at 25 °C. The labeled lipids were extracted, subjected to mild alkaline hydrolysis and separated by TLC with solvent system I (d). Fractions containing sphingoid bases (DHS, sphingosine) and IPCs in (d) were collected from the silica. The fraction containing IPCs but not sphingoid bases was subjected to strong HCl hydrolysis. Samples were separated by TLC with solvent system II (e).