Isotope tagging for relative and

The technique of isobaric tag for relative and absolute quantification (iTRAQ) is based on covalently labeling the amines at N-termini and the side chains of peptides with isotope-coded tags after the proteins have been isolated form biological systems, denatured, and enzymatically digested. Here the isotope labeling is carried out at a much later stage than in both SILAC and ICAT. iTRAQ is an MS/MS technique that uses CID-derived ions for both the identification and quantification of proteins. 

Some popular quantitative methods in proteomics are based on derivatization with agents containing a stable isotope. In this respect, isotope-coded affinity tags (ICAT) have been widely used [121], as have isobaric tags for relative and absolute quantitation (iTRAQ) [122]. 

Labelling the 3-APTHS molecule with "OH groups provides an isotopic tag at the site on the molecule where cross-linking should take place. 3-APTHS hydrolyzed in 97.8 at %, 80 labelled water was spun onto sample substrates in the manner described above and SSIMS spectra were acquired both at room temperature and after heating of the sample to 100°C in vacuum for 1 h. The relative intensity of the oxygen containing ions produced by these samples can be... 

H and an acid-cleavable biotin moiety. Insertion of an acid-labile linker greatly decreases the elution of nonspecifically bound peptides from avidin affinity materials. Isotope-coded protein labels differentially label all of the free amino groups on proteins for relative quantitation (103). This method does not require an affinity tag. 

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