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.

Stable Isotope-Labeled Peptides and Protein Reagents/Kits

➤ Stable Isotope Standards for Mass Spectrometry
➤ Preloaded Resins

Application Note
➤ Selection and Synthesis to Analysis: Stable Isotope-Labeled Peptides for Proteomic Applications

Researcher Perspectives
➤ Synthetic Peptides As Internal Standards

Peptide Synthesis Materials view all

❛❛The commercial availability of stable isotope-labeled amino acids with very high isotopic purity has revolutionized quantitative proteomics. From their use in metabolic labeling of cells and rodents for differential discovery proteomics, to their use in synthetic peptides as internal standards for targeted analysis of proteins, isotopically labeled amino acids make it possible to measure, with very high precision, changes in the levels of peptides and the proteins they are derived from in highly complex samples such as cell lysates, tissue, and plasma. Cambridge Isotope Labs has been and continues to be a leader in the commercial production of labeled amino acids and other labeled compounds.❜❜

– Stephen A. Carr, PhD | Senior Director of Proteomics, Broad Institute of MIT and Harvard

Frequently Asked Questions

Does CIL provide catalog and custom-labeled peptides? A few stable isotope-labeled peptides are available off-the-shelf (e.g., oxidized and reduced glutathione). CIL is pleased to supply highly enriched and pure amino acids (both free and protected) to the world’s leading peptide manufacturers for synthesis activities, but does not custom synthesize peptides in-house.

Would 0.8 mM of lysine or arginine preloaded resins provide approximately 8 synthesis at 0.1 mM scale?Yes, theoretically 0.8 mM of resin would provide 8 synthesis at 0.1 mM scale. Final yields are always dependent on actual sequence and the efficiency of the couplings.

Does CIL provide catalog and custom preloaded resins? Yes. Through collaboration with BioSynth, CIL is pleased to offer synthesis-ready preloaded resins. For a list of our catalog offerings, please refer to our Preloaded Resins flyer.

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Yeom, S.; Nam, D.; Bok, K.H.; et al. 2023. Synthesis of S-carbamidomethyl cysteine and its use for quantification of cysteinyl peptides by targeted proteomics. Anal Chem, 95(38), 14413-14420. PMID: 37707799
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Yussif, B.M.; Checco, J.W. 2022. Evaluation of endogenous peptide stereochemistry using liquid chromatography-mass spectrometry-based spiking experiments. Methods Enzymol, 663, 205-234. PMID: 35168790
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