Mass Spectrometry Analysis of Chloroplast Synthesized Human IGF-1. The 7, 14 and 25 kDa protein bands were trypsin-digested and evaluated by mass spectrometry. The top panel is the pure MS without fragmentation. The second panel shows all of the significant MS/MS events derived from the MS scans. The third panel shows the MS/MS events that yielded a fragment with m/z 1421 +/- 1 mu. These were all grouped together in one cluster eluting at 55.32. S. aureus protein A was found in all spots examined and the active portion of IGF-1 was identified. In at least two of the spots analyzed, human IGF-1 and S. aureus Z-tag was detected. Shown are full MS and MS/MS patterns for discovery of peptide 105–116 with an elution time of 55.32 for a single charge mass of 1421.1 and a double charge mass of 711.6.