Cellular proteins are far from static entities; and are constantly undergoing synthesis and degradation. Changes in the rates that proteins are 'turned over' are central to understanding protein regulation in response to perturbations or stimuli.
Alterations in global protein turnover rates are key to understanding how a cell responds to a specific treatment. Conversely, identifying changes in the turnover of specific proteins can aid in determining which pathways are involved in a particular process.
Pulse labelling with SILAC is a powerful tool to assess global changes in protein turnover. Cells are grown in light (L) (1 dish) or medium (M) (1 dish per time point) SILAC media (A). The media in the dishes containing the cells grown in the medium (M) media is then changed to heavy (H) media at a different time point for each dish.
Following analysis of the samples by LC-MSMS, a curve of the measured SILAC ratios (B) vs. time can be modelled (C). The half lives of both the newly-synthesised and degraded proteins can thus be determined. In addition, information on the proteins that are not turned over is provided.