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.