Enzymatic Labeling

The incorporation of ¹⁸O atoms into a C-terminus of peptides has emerged as one of the labeling strategies used in comparative quantitative proteomics. The success of this enzymatic labeling technique is due in part to the relative low cost of ¹⁸O water, the resulting mass increase in molecular weight for a “heavy” peptide, and the co-elution of ¹⁸O/¹⁶O peptide pairs in a liquid chromatography (LC)-based mass spectrometry (MS) experiment.