Expression of wild-type hamster LCB1 and its C133Y or C133W mutant in LY-B cells. LY-B cells were transfected with various plasmids and analyzed. As controls, untransfected LY-B and wild-type CHO-K1 cells were also analyzed. Lanes 1 and 2 represent untransfected CHO-K1 and LY-B cells, respectively. Lanes 3, 4, 5, and 6 represent LY-B cells transfected with pSV-OK (empty vector), pSV-cLCB1, pSV-cLCB1C133Y, and pSV-cLCB1C133W, respectively. (a) Western blotting of the LCB1 subunit. Each lane was loaded with 20 μg protein of cell lysate. (b) Metabolic labeling of lipids. After incubation of cells with L-[14C(U)]serine for 2 hours, lipids were extracted from the cells and separated by TLC. The radioactive image of lipids on the TLC plate is shown. PE, phosphatidylethanolamine. (c) SPT activity in cell lysate. Data shown are from triplicate experiments.