Research Resource: Identification of Novel Growth Hormone-Regulated Phosphorylation Sites by Quantitative Phosphoproteomics

Ray, Bridgette N.; Kweon, Hye Kyong; Argetsinger, Lawrence S.; Fingar, Diane C.; Andrews, Philip C.; Carter-Su, Christin

In the first and second 5-min trials, 65 and 148 GHregulated phosphorylation sites were observed, respectively, and 14 sites were present in both 5-min trials (Supplemental Tables 1 and 2 ). With the highly complex peptide mixtures obtained from cell lysates, a mass spectrometer obtains sequence from only a small fraction of the phosphopeptides present in the sample (47) . For studies in which similar numbers of phosphosites are identified in the various individual trials, the fraction of the phosphosites identified in the replicate trials gives an indication of the extent to which the study has sampled the phosphoproteome of the cell type. Because only a small fraction of the phosphoproteome of the cell is normally sampled, the detection of a phosphorylated residue in even a single trial is noteworthy.