Fig. 2. ESI-MS spectra of G41C CaM (A) and (C) and G114C CaM (B) and (D) mutants before ((A) and (B), calculated 17 095 Da) and after ((C) and (D), calculated 17 522.3 Da) modification by FL. The X-ray structure of Ca²⁺-bound CaM (PDB code 1EXR) and the chemical structure of FL are shown as insets to highlight the positions of Gly41 and Gly114 and the chemical modifications.