ICAT-labeled peptides were analyzed by µLC-ESI-MS/MS. Peptides were separated by on-line reversed-phase chromatography using a 75 µm x 10 cm self-packed Magic C18AQ column (Michrom BioResources) at a flow rate of 300 nL/min. Peptide fragmentation by collision-induced dissociation was performed in an automated fashion using the dynamic-exclusion option from the full-range MS spectra or by GPFm/z using an ion trap mass spectrometer (Thermofinnigan; Yi et al., 2002).