Stable isotope labeling by amino acids in cell culture

In contrast, the second population is fed with growth medium containing amino acids labeled with stable (non-radioactive) heavy isotopes.

[6] SILAC has emerged as a very powerful method to study cell signaling, post translation modifications such as phosphorylation,[6][7] protein–protein interaction and regulation of gene expression.

[9] It has also been adapted as a 'forward+reverse' SILAC method for simultaneous labeling of host and microbe, which enables the study of host-microbe interactions.

Recently, a new technique called NeuCode (neutron encoding) SILAC, has augmented the level of multiplexing achievable with metabolic labeling (up to 4).

The increased multiplexing capability of NeuCode amino acids is from the use of mass defects from extra neutrons in the stable isotopes.

The principle of SILAC . Cells are differentially labeled by growing them in light medium with normal arginine (Arg-0, blue color) or medium with heavy arginine (Arg-6, red color). Metabolic incorporation of the amino acids into the proteins results in a mass shift of the corresponding peptides. This mass shift can be detected by a mass spectrometer as indicated by the depicted mass spectra. When both samples are combined, the ratio of peak intensities in the mass spectrum reflects the relative protein abundance. In this example, the labeled protein has the same abundance in both samples (ratio 1).