The binding of cupric, nickel and zinc ions to tryptophan, tyrosine, and various di- and tri-peptides containing these amino acids have been studies by fluorescence quenching. The proton dissociation constants have been determined for the ligands by fluorescence titration. The association constants of the metal ions for the various ligands have been determined by curve fitting to the quenching data in the case of copper and nickel ions. Zinc ion complex association constants were obtained by competition experiments. This relatively novel method for measuring the strength of binding is relevant not only to the interaction of metal ions and peptides, but binding equilibria in general. The strong interaction of melittin with bilayer phospholipid membranes was shown by the release of a fluorescent dye from liposomes. Only a small number of melittin molecules were needed to effect dye release, indicating that the peptide formed channels through the membrane. Calmodulin formed a complex with melittin, thus inhibiting the latter's ability to lyse liposomes. A sensitive assay for calmodulin has been developed based on this phenomenon. The calmodulin-melittin complex is disrupted in the presence of phospholipid. The kinetics of this process are being studied by fluorescence anisotropy and stopped-flow measurements.
