Figure 2: Identification of phosphoprotein integrin beta 4 isoform 3 by LC-MS/MS. Twenty-seven phosphospectra (corresponding to 19 unique phosphopeptides) were matched to integrin beta 4 isoform 3 in CFPAC-1 cells, and 6 (corresponding to 4 unique phosphopeptides) in normal duct cells. (a) Example CID spectrum of the phosphopeptide MDFAFPGS#TNSLHR (2+ ion m/z 830.3493) obtained from normal duct cells; (b) CID spectrum of the phosphopeptide VLS#TSSTLTR (2+ ion m/z 572.7811) obtained from CFPAC-1 cells. The spectrum is labeled to show singly-charged b and y ions, as well as ions corresponding to neutral loss of water and phosphate group.