Amino acid-coded mass tagging

Gu, S Du, Y Chen, J., Liu, Z Bradbury, E.M., Hu, C.A., Chen, X. (2004). Large-scale quantitative proteomic study of PUMA-induced apoptosis using two-dimensional liquid chromatography—mass spectrometry coupled with amino acid-coded mass tagging. J. Proteome Res. 3, 1191 1200. 

Isotope-Coded Affinity Tagging and Amino Acid-Coded Mass Tagging 111... 

Labeling proteins with heavy and light tags and screening the hit compound versus an inactive control, followed by mass spectrometric comparison of the two samples, is another approach that avoids many of the common pitfalls in affinity methods (3). Techniques such as stable isotope labeling with amino acids in cell culture and isotope-coded affinity tagging (ICAT) exemplify these techniques. 

Certain methodologies used in conjunction to protein profiling by mass spectrometry. There are several methods to label proteins that assist their profiling by mass spectrometry. These methods involve labeling of proteins in vitro or in vivo with an isotope. Some of these techniques include Isotope Coded Affinity Tag (ICAT) and Stable Isotope Labeling with amino acids in Cell culture (SILAC). These are described below. 

Sulfur exists in cysteine and methionine and is one of the most abundant elements in natural proteins. The cumulative abundance of sulfur in proteins is about 5%. The relative amount of proteins can be obtained by the isotopelabeling method with the sulfhydryl group and molecular mass spectrometry measurement, such as the isotope-coded affinity tags (ICAT) method. On the other hand, when the amino acid sequence of a protein has been identified, the absolute amount of a protein can be obtained via the determination of sulfur with ICP-MS. In comparison with other naturally existing elements in proteins, sulfur is preferable as an internal standard for protein quantification due to its high abundance. ... 

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