GroEL analyzed by MALDI TOF-TOF. (A) Total protein coverage of GroEL was 46 percent. YVASGMNPMDLK was observed by MALDI MSMS without methionine oxidation. (B and C) CID MSMS spectra of YVASGMNPMDLK with a mass of 1325.6 m/z. Fragment b and y ions that matched predicted b and y ions are highlighted in blue and red respectively.