By using amino acids where one or more carbon or nitrogen atoms are replaced with stable isotopes, your peptide is thought to retain all its physiochemical properties except for a shift in its mass. The desired mass shift is typically in the order of 5-10 Da, but could be any number you like, provided that cost is not an issue. As an example, we have the Apelin 13 peptide, where a mass shift of 12 Da is obtained by labelling two Prolines with the stable isotopes 13C and 15N.
It should be noted that, when it comes to cost, it makes a difference which amino acid is labelled. For example, Arg 13C615N4 which adds 10 Da to the molecular mass will cost in excess of 10 times more than Phe 13C915N1, which gives the same shift in mass. When you turn to us for making these isotope labelled peptides, we will come up with more cost effective alternatives if they should exist.
A point of consideration is the quality of the reagents used. When producing high quality peptides, this is always important, but for peptides with stable isotopes this becomes pivotal. Since the labelled and un-labelled peptide have identical physiochemical properties, except for the mass shift, it is not possible to purify the material by HPLC in order to separate the two. You need the 98-99% isotopic purity of the reagents or you simply will not be able to obtain the high quality peptide that you require for your MS experiments.
Stable isotope labelled peptides are often used as standards and it may be desirable to know how much target peptide is present in a given amount of lyophilized peptide powder. Since the powder contains counter ions and bound water as well as peptide material, the net peptide content is not known beforehand. An elemental analysis or amino acid analysis could be made in order to determine the ratio.
Innovagen has serviced the research community since 1992. Over the years we have seen the importance of thinking quality in every step of the production of synthetic peptides. You will particularly benefit from our experience when it comes to isotope labelled peptides. Please take a few moments to read about our view on production of high quality peptides.
Examples of references of customers using our custom synthesis service for peptides containing stable isotopes, include;
Seip, Knut F., et al.
"Bradykinin analysis revived–A validated method for determination of its stable metabolite in whole blood by LC–MS/MS."
Journal of Chromatography B 947 (2014): 139-144.
Dahlfors, Gunilla, et al.
"Validation of a competitive ELISA assay for the quantification of human serum hepcidin."
Scandinavian journal of clinical and laboratory investigation (2015): 1-7.
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