Post-translational modifications are the chemical modifications of proteins subsequent to their biosynthesis. The modification of certain amino acid residues may result in changes of the protein conformation and/or its capacity to interact with other proteins or ligands, to be active or inactive in the case of an enzyme, to allow or interfere with gene expression and many other biological functions. These modifications have been found by using radioactively labeled compounds, to yield a protein(s) carrying a radioactive tag located in the modifying group and that can be detected by methods such as autoradiography, liquid scintillation, and other methods after resolution of the different compounds by electrophoresis, chromatography and other separation procedures. 
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