Intrinsic specificity of Ca2+–protein binding sites

The gas-phase chemistry of anionic M + Cat²⁺ – 3H]^? complexes between Ca²⁺-specific peptides and the alkaline earth metal ions Mg²⁺, Ca²⁺ and Ba²⁺ is reported. The metal ion complexes were studied using fast atom bombardment, collision-induced decomposition (CID) and molecular mechanical calculations. The CID reactions and molecular mechanical calculations revealed that the Ca²⁺–peptide complexes are bound differently to the Mg²⁺– and Ba²⁺–peptide complexes and that the intrinsic (gas-phase) chemistry is reflected by known aqueousphase chemistry.