Isotopically labeled standards for proteomic measurements can be prepared chemically. This can be achieved at the peptide or protein level by solid phase synthesis or recombinant gene expression, respectively. To aid the synthesis of stable isotope-labeled peptides, CIL offers an array of protected amino acids and preloaded resins. For the expression of stable isotope-labeled proteins, we offer media as well as cell-free protein expression reagents and kits from CellFree Sciences Co., Ltd. CIL also offers select stable isotope-labeled peptides (e.g., oxidized and reduced glutathione) and full-length proteins (e.g., C-reactive protein or CRP) for use in bottom-up LC-MS experiments. The synthesis/expression products are described and referenced on their associated pages.
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.
Protein Expression and Standards
Stable isotope-labeled cellular biomass can be used in both proteomic and metabolomic investigations. In addition, quantitative, proteomic MS-based studies can benefit greatly from the use of purified, labeled intact protein as internal standards.