Figure 1.

A schematic representation of the SILAC (‘stable-isotope labelling in cell culture’) method. A stably labelled amino acid in a cell-culture medium (in this case, ‘heavy’ arginine or lysine) is incorporated fully into the proteome of one cell population (“Cell pop 2”). Relative quantification experiments can easily be carried out using cells that were grown in normal media as the control (Cell pop 1). Cell lysates from two conditions can be combined and purified through many steps. The proteins are then digested and if the two forms of the peptides co-elute, a peptide ratio can be obtained for each mass spectrum, which allows the protein levels in the two populations to be quantified relative to each other.