Peptide Labeling with Improved 18O Incorporation Method

To optimize the 18O-labeling method, two key aspects, peptide dispersion and trypsin deactivation, were discussed. The addition of RapiGest™ SF in H218O and microwave heating enhanced labeling efficiency of α-casein digested peptides (18O/16O ratio > 99%). Chemical modification with tris (2-carboxyethyl) phosphine and iodoacetamide resulted in trypsin deactivation completely. No significant back-exchange from 18O to 16O was observed after labeled in 6 days. The experiment result with peptide mixture from thyroglobulin showed that the improved method could be effectively used to label protein and peptide.