Stable Isotope Labeling

Stable isotope-labeled compounds containing deuterium, carbon-13, and nitrogen-15 have been successfully used in clinical pharmacology for measuring drug fate and degradation, determining mechanisms of action, the bioavailability of drugs and drug delivery systems, and the metabolism of toxins. Beyond clinical applications, isotope-labeled compounds have been increasingly used to study the fate of contaminants in the environment and trophic pathways (i.e., bioaccumulation, biomagnification, etc.).

SILAC stands for Stable Isotope Labeling with Amino Acids in Cell Culture. It is also called Metabolic Labeling and it uses non-radioactive isotopes such as 13C6,15N2-lysine and 13C6,15N4-arginine in the culture medium with the purpose of incorporating the stable isotopes during protein synthesis. In contrast to radiolabeled compounds, SILAC compounds do not require expensive protective materials, handling facilities, or safety training.

Classical SILAC experiments are popular for quantitative proteomics and use stable isotope-labeled amino acids to label the entire proteome of a cell culture or isotope-labeled proteins to tag only specific pathways in a cell. Coupled with mass spectrometry, classical SILAC measures differential protein abundances between labeled and unlabeled cell lysates. The applications of this method range from the elucidation of metabolic pathways to measuring protein-mediated cell-cell interactions and even detecting important post-translational modifications.