isotope labeled residue A protein modification that effectively substitutes atoms of particular common isotopes with atoms or groups containing isotopes that are not the most common. In SILAC (stable isotope labelling of amino acids in cell culture), the label may be introduced either through labeling of an incorporated residue or labeling of the substrates in a metabolic modification. For isotope labeling introduced through a modification reagent see MOD:01426. IsoTagRes MOD:00702 PSI-MOD SILAC protein modification categorized by chemical process