SILAC: Stable isotope labeling with amino acids in cell culture (SILAC) is a simple and straightforward approach for in vivo incorporation of a label into proteins for mass spectrometry (MS)-based quantitative proteomics.

SILAC relies on metabolic incorporation of a given 'light' or 'heavy' form of the amino acid into the proteins. The method relies on the incorporation of amino acids with substituted stable isotopic nuclei (e.g., deuterium, ¹³C, ¹⁵N). Thus in an experiment, two cell populations are grown in culture media that are identical except that one of them contains a 'light' and the other a 'heavy' form of a particular amino acid (e.g. ¹²C and ¹³C labeled L-arginine, respectively).

When the labeled analog of an amino acid is supplied to cells in culture instead of the natural amino acid, it is incorporated into all newly synthesized proteins. Since there is hardly any chemical difference between the labeled amino acid and the natural amino acid isotopes, the cells behave exactly like the control cell population grown in the presence of normal amino acid.

Sample digestion and analysis as described above (Protein identification) can then yield % incorporation of the 'heavy' amino acid into any observed protein, which in turn is proportional to the biosynthetic rate of that protein during the course of the experiment.

Read more: http://en.wikipedia.org/wiki/SILAC
By appointment only. Contact Norm

SILAC alternative: iTRAQ 

A 'quantitative proteomics' alternative to SILAC, useful in situations when it is not possible to incorporate labeled amino acids, is known as iTRAQ. The iTRAQ™ protocol available at the GSL uses four reporter ions of 114, 115, 116 and 117 Da.

One advantage of iTRAQ over SILAC and metabolic labelling is that upto four samples can be analyzed simultaneously, thereby reducing the amount of mass spectrometry time needed for analysis. In addition, the b- and y- ions derived from peptides labelled with the four iTRAQ tags are indistinguishable, resulting in higher MS/MS intensity and therefore more confident peptide identifications in comparison to SILAC and metabolic labelling, in which the MS/MS spectra for the differentially labelled peptides are acquired independently. Results are reported as relative levels of all identified proteins across the multiplexed samples. Follow the links below to learn more.

We strongly recommend the analysis of a non-labeled sample prior to use of the iTRAQ reagents so that the investigator may gauge protein coverage for their samples. 

iTRAQ Protocol Manual 

Tandem Mass Tags (TMT) technology

We now support Tandem Mass Tag technology as an alternative to iTRAQ.

Further information can be found here.