Fig. 44

Schematic outlines showing typical workflows for quantitative proteomics from cells or tissues (from protein extraction, trypsin digestion and/or isotope labeling to MS analysis). Label-free quantitation individually analyzes samples and compares the data using multiple approaches like spectral counting and peak intensities. As unlabeled samples are individually analyzed in label-free workflows, the steps must be tightly controlled to avoid biasness. Conversely, labeled protein quantification is characterized by the isotopic labeling of proteins either after protein extraction or in live cell condition. Then, the labeled samples are combined and processed for quantitative analysis. The red and the green colors represent heavy and light isotopes, respectively, for differential labeling and comparison