Evaluation of a cleavable stable isotope labeled synthetic peptide for absolute protein quantification using LC-MS/MS.

Protein cleavage coupled with isotope dilution mass spectrometry (PC-IDMS) has the potential to provide the absolute concentration of a specific protein, or multiple proteins, in complex mixtures. However, PC-IDMS differs from standard IDMS since the internal standard is a different molecule than the analyte at the start of the experiment, more specifically, the internal standard is a peptide and the analyte is a protein prior to cleavage. It is not until after the cleavage process that the stable isotope labeled synthetic peptide has the same physicochemical behavior as the peptide cleaved from the protein. The work presented here evaluates the use of tryptic cleavage sites incorporated into the internal standard synthetic peptide in an attempt to create an internal standard that has cleavage characteristics more similar to the protein being quantified. Results presented here suggest that an internal standard synthetic peptide incorporating internal cleavage sites does not improve the accuracy and precision of the values obtained when performing PC-IDMS.