title: Relative calcium-binding strengths of amino acids determined using the kinetic method.
abstract: We have measured the relative calcium-binding energies of amino acids using tandem mass spectrometry of Ca(2+)-bound trimeric amino acids. Although calcium-bound dimeric amino acid complexes coordinated too strongly to allow observation of the two competing dissociation products (calcium-bound monomeric ions) required for analysis of their metal binding affinities using the conventional kinetic method, the Ca(2+)-bound trimeric cluster ions dissociated readily to form dimeric cluster ions through simple ligand losses. The calcium-binding energies were obtained by comparing the ratio of the [Ca(2+)(A(1))(2) - H(+)](+) and [Ca(2+) (A(1))(A(2)) - H(+)](+) ions that dissociated from the [Ca(2+) (A(1))(2)(A(2)) - H(+)](+) ion and the ratio of the [Ca(2+)(A(2))(2) - H(+)](+) and [Ca(2+)(A(1)) (A(2)) - H(+)](+) ions that dissociated from the [Ca(2+)(A(1))(A(2))(2) - H(+)](+) ion, where A(1) and A(2) represent two amino acids. The energies deduced from this analysis represent the relative average binding energies of complexes having the form [Ca(2+)(A(1))(2) - H(+)](+). The relative Ca(2+)-binding strengths of the alpha-amino acid complexes follow the order Cys < Ser < Thr < Ile < Leu < Val < Gly < Ala < Pro < Phe < Met < Tyr < Asn < His < Gln < Trp < Lys < Arg. To our knowledge, this report provides the first example of using kinetic methods to determine the relative binding strengths of divalent metal-amino acid complexes.
authors.affiliation: Department of Chemistry, National Dong Hwa University, Hualien 974, Taiwan.
authors.forename: Yen-Peng
authors.initials: YP
authors.lastname: Ho
authors.forename: Ming-Wei
authors.initials: MW
authors.lastname: Yang
authors.forename: Li-Ting
authors.initials: LT
authors.lastname: Chen
authors.forename: Yu-Chuan
authors.initials: YC
authors.lastname: Yang
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry*; D003198:Computer Simulation; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D000596:Amino Acids; D002118:Calcium