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Peptides labeled with stable, non-radioactive isotopes are increasingly used for convenient detection in research. Isotope–labeled, or ‘heavy’ amino acids, are derived from natural amino acids by substitution of certain atoms (N, C, H) with their ‘heavy isotope’ variant. The most frequently substitutions are 12C by 13C (carbon-13), 14N by 15N (nitrogen-15), and 1H by 2H (deuterium).
Stable-isotope-labeled (SIL) peptides display identical physiochemical properties and chemical reactivity as their non-labeled counterparts (apart from a few exceptions). However, under certain conditions the minute mass difference make labeled and unlabeled peptides behave differently. This constitutes the basis for using SIL-peptides in a variety of absolute quantification applications such as quantitative proteomics, the quantification of complex protein mixture at very low concentration, or NMR studies.
At company we have produced thousands of such custom ‘heavy’ peptides. These SIL-peptides are synthesized using only the highly enriched stable amino acids from premium supplier Cambridge Isotope Laboratories (CIL) for the Fmoc-based solid-phase peptide-synthesis in our laboratory. These uniformly labeled amino acids all have over 99% isotopic purity.
These important attributes have enabled us to successfully respond to the ever changing demand for high quality SIL-compounds. All stable isotope labeled peptides undergo mass spectrometric analysis and stringent analytical HPLC to establish the final purity, and to assure that our customers receive only the highest quality peptides for absolute quantitation.
The table below lists the most common SIL amino acids
|Amino Acid||Code||Mass Difference||Isotope||Isotopic Enrichment|
|Alanine||A||+4Da||U- 13C3, 15N||>99%|
|Arginine||R||+10Da||U- 13C6, 15N4||>99%|
|Isoleucine||I||+7Da||U- 13C6, 15N||>99%|
|Leucine||L||+8Da||U- 13C6, 15N||>99%|
|Lysine||K||+8Da||U- 13C6, 15N2||>99%|
|Phenylalanine||F||+10Da||U- 13C9, 15N||>99%|
|Proline||P||+6Da||U- 13C5, 15N||>99%|
|Valine||V||+6Da||U- 13C5, 15N||>99%|