Updated project metadata. MCF7 cells were grown in culture under low pH and physiological pH conditions in order to generate candidate biomarkers for tumor acidosis. SILAC was used to enable comparison of protein expression levels using relative quantification. Two biological replicates were prepared using "label flipping," and each fraction was analyzed in duplicate by LC-MS/MS. Sample nomenclature includes N for "normal" or physiological pH versus L for low pH as the first letter with H for "heavy" and L for "light" as the second letter. Therefore, one experiment is described as NH-LL, while the other is NL-LH. Fifteen IEF fractions were generated and analyzed with LC-MS/MS (RSLC and Orbitrap, Thermo) for each SILAC pair .