MALDI-TOF MS profile of crude peptide extracts from O. affinis leaves. The calculated (Calc) and observed (Obsv) monoisotopic masses for the cyclotides kalata B1, B2 and B3 are included and serve as internal controls. Peaks for kalata B6 (kB6) and kalata B7 (kB7) are marked without mass data. The calculated mass for kalata B19 (3092.34) is close to a mass in this profile (3091.47), but when its error (represented as ppm) is compared to the errors of other cyclotides in the same profile, the difference between calculated and observed is too great for this mass to be B19.
Qin et al. BMC Genomics 2010 11:111 doi:10.1186/1471-2164-11-111