Characterization of Clinically-Relevant Stable Isotope Labeled Recombinant Proteins for Use as Internal Standards in Quantitative MS Workflows

Methods for quantification of clinical protein biomarkers by mass spectrometry demand a high level of analytical quality. Procedures must be developed to minimize and control experimental variations in all steps of the workflow including protein extraction, fractionation, enrichment, proteolysis and analysis. To this end, we have characterized stable isotope labeled (SIL) full length proteins for utility as internal standards in quantititative MS workflows. These SIL proteins can be spiked at the initial stage of the analytical workflow to significantly minimize variations. Clinically-relevant SIL proteins expressed in E. coli, such as IGF1, and in mammalian HEK293 cells, such as Thyroglobulin and APOA1, have been characterized in this study.