ISOMIX® Proteome References

The usage of stable isotope labeling and MS in proteomics facilitates the quantitation of changes in protein levels in biological systems. As such, quantitative proteomics involves the determination of absolute differences in global protein expression of cells, often as a consequence of endogenous or exogenous stimuli. The combined application of stable isotope labeling and MS in proteomics has enabled researchers to make quantitative comparisons in protein levels between multiple biological samples. Incorporation of “heavy” stable isotopes such as 13C, and 15N into proteins for mass spectrometric analysis is accomplished by the attachment of site-specific tags (4), metabolic labeling (5), and enzymatic reactions (6-8). For quantitative methodologies, two separate samples – one produced with “heavy” isotopes used as internal controls and the other with “light” or the natural abundance isotopes – are examined. The samples are combined prior to mass spectrometric analysis and doublet peaks observed in the mass spectrum originating from identical “light”, and “heavy” peptide fragments are compared. The ratio of the “light” and “heavy” isotopic peak intensities for a particular peptide provides relative measurement of protein abundance in a given spectrum. This approach permits the simultaneous evaluation of numerous proteins from defined biological states. Advances in global metabolic labeling methodologies combined with improved instrumentation greatly expand the scope and potential of quantitative proteomics.

We remain committed to advancing scientific study by providing the MS community with high-quality, isotopically labeled human and mouse proteome mixture reference products ISOMIX for use in quantitative proteomics studies. The ISOMIX contains whole proteome with > 99.9% heavy R&K labeling ratio and the complete Mass spectrometry data sets. The heavy isotope labeled ISOMIX references can be used for any quantitative mass spectrometry applications.