Isotope Labeled Aqua Internal Standard Peptide

While isotope methods establish only relative quantification of expressed proteins, the absolute quantification (AQUA) strategy can provide information for the precise determination of protein expression and post-translational modification levels. The AQUA method relies on the use of a synthetic internal standard peptide that is introduced at a known concentration to cell lysates during digestion. Analysis of the proteolyzed sample by a selected reaction monitoring (SRM) experiment in a tandem mass spectrometer results in the direct detection and quantification of both the native peptide and isotope labeled AQUA internal standard peptide.