Figure 3.

Time course of PC remodeling in live yeast cells at 30°C as recorded by ESI-MS/MS in pulse-chase experiments addressing PC synthesized by methylation of PE. Cells from pct1 pYES2 (empty vector control) (A), pct1 pYES2-SCT1 (B), and pct1plb1 pYES2-SCT1 (C) strains cultured in galactose-containing medium to induce overexpression of SCT1 from the GAL1 promoter (B and C), were pulsed for 10 minutes with (methyl-D₃)-methionine. After rapid removal of the label, cells were chased in the presence of unlabeled methionine for the time intervals indicated. Molecular species profiles of (methyl-D₃)₃-PC and steady-state PC (blue bars) were analyzed by parent ion scanning of total lipid extracts in the positive ion mode at m/z 193 and 184, respectively (molecular species of PC are indicated by the total number of acyl carbon atoms:total number of double bonds). The overexpression of Sct1p slows down growth. The experimental conditions were such that the doubling time of the overexpressing strains was approximately 1.3× that of the empty vector control; deletion of PLB1 did not affect the growth rate. Data were taken from ref. 51.