Identification and quantitation of ribosomal protein S6 kinase in NPM/ALK-transfected cells by ICAT-MS/MS. Data-dependent MS full scan and MS/MS sequencing scans for one ICAT pair identified ribosomal protein S6 kinase as 1.7-fold overexpressed (inset) in the NPM/ALK-positive cell lysate in comparison with NPM/ALK-negative cells. The b ion series (blue) and the y ion series (red) match the tryptic peptide AYSFCGTVEYMAPEVVNR. The b ion series represent peptide fragment ions wherein the positive charge is maintained on the N-terminus (blue m/z peaks and numbers). The y ion series represent the fragment ions where the positive charge is retained on C-terminus (red m/z peaks and numbers). The differences between successive b or y ions in a series indicate the m/z of the individual amino acid residues. In the bottom panel, column 1 (AA) represents amino acid residue. Column 2 represents the position of the amino acid residue in the peptide identified read in the N-to-C-terminal direction. Column 3 represents the m/z of the peptide at a specific amino acid position in the identified peptide read from an N-to-C-terminal direction. Column 4 represents the m/z of the peptide at a specific amino acid position C-to-N-terminal direction. Column 5 represents the position of the amino acid residue in the peptide read from the C-to-N-terminal direction.