Strategy for affinity purification using GST- CPE
as "bait". For affinity purification, one cell population is grown in medium containing [12C]arginine and [12C]lysine, whereas the other is grown in medium supplemented with [13C]arginine and [13C]lysine. Bound proteins of both pull-down fractions are combined and separated by SDS-PAGE. After tryptic in-gel digestion, proteins are identified by LC-MS/MS, and the ratios of their abundance are quantified from MS peak intensities.