Figure 1. Quantification of Endogenous EGFR in HCC827 NSCLC Cells using SIS and SCAR Peptides.

LC-MRM total ion chromatograms for the endogenous peptide (A), SIS peptide (B), and SCAR peptide (C). MS/MS data averaged over one minute of acquisition time for the endogenous peptide (D), SIS peptide (E), and SCAR peptide (F). The distribution of charge retention is plotted using b vs. y-ion signal for the three peptides (G), then y-ion data were further analyzed to compare individual transitions. All transitions were similar except for y₇ in which the SIS peptide showed higher peak intensity, and y₉ in which the SCAR peptide showed higher intensity (H). A dilution series of the peptide set shows similar peak areas for all three peptides, resulting in accurate absolute quantification by each internal standard (I). EGFR expression in lysate from the HCC827 lung cancer cell line was analyzed by both internal standards; no significant difference was found between the two calculations (J).