title: Evidence that divalent cations bind to diphtheria toxin: an ESR approach.
abstract: We have used electron spin resonance (ESR) techniques to study the binding of divalent cations to diphtheria toxin (DT). Addition of DT to Mn(II) solution at a stoichiometry of 2:1 (DT:Mn) induces a 79% loss in the intensity of the ESR spectrum of Mn(II) suggesting a strong binding of Mn(II) to DT. Inclusion of Ca(II) at a ratio of 1:2:1 (Ca:DT:Mn) in the reaction mixture restores the intensity of the Mn(II) signal to 64%. This indicates that Ca(II) and Mn(II) share same binding site(s) in DT. The results presented in this communication suggest that DT is a Ca(II) binding protein.
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D004167:Diphtheria Toxin / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D008345:Manganese / Q000378:metabolism*
chemical_list: D004167:Diphtheria Toxin; D008345:Manganese; D002118:Calcium