Proteins are not just static, they get turned-over on a constant basis. Changes in their turnover rate are often central to their regulation in response to perturbations. A famous example: the “guardian of the genome,” p53.
Changes in global protein turnover rates can be crucial in understanding the cellular response to a specific treatment. By contrast, when only the turnover of specific proteins is affected, identifying these can help map the pathways involved.
SILAC labelling is a powerful tool to assess global changes in protein turnover: Cells are grown in L (1 dish) or M (1 dish per time point) SILAC medium (A). The medium of the M SILAC dishes is then changed to H SILAC medium at a different time-point for each dish.
After mass spectrometry analysis, the curve of measured SILAC Ratios (B) vs Time can be modelled (C) to determine half-lives of synthesis and degradation as well as eventual non-turned over fraction.