Peptide Synthesis

Targeted mass spectrometry (MS) isotope analysis (i.e., selected or multiple reaction monitoring, SRM or MRM) is an alternative to antibody-based assays for the verification/validation of putative protein biomarkers, but it also has been employed for discovery-based proteomics (see example references below). One obstacle of this strategy is that every peptide possesses unique biochemical characteristics. Its amino acid composition and possible post-translational modifications defines its elution profile from the liquid chromatography column, ionization, and fragmentation. For developing a clinically relevant MS assay, these peptide properties must be characterized with a synthesized peptide before analyzing the peptide of interest in vivo. The synthesis of labeled peptides is aided by the use of isotope-enriched protected amino acids or preloaded resins in solid phase productions. Absolute quantitation of peptides/proteins in biological samples can then be achieved by application of these heavy peptides.