Dynamic properties and membrane activity of ion specific antibiotics

Abstract

Abstract Conformational rearrangements of membrane‐active peptide and depsipeptide antibiotics such as enniatin B, valinomycin, and valine‐gramicidin A have been studied as a function of solvent polarity employing ultrasonic absorption methods. The results provide information about the number of occupied conformational states and their respective rates of interconversion. The interpretation of the results from kinetic measurements was confirmed by spectroscopic studies. The remarkable differences in the stabilities of the various cation complexes of depsipeptide antibiotics bound to lecithin vesicles as well as in homogeneous solution were related to different conformations of the ligands in these complexes as characterized by spectroscopic techniques. Kinetic studies by relaxation methods led to the elucidation of the mechanism of complex formation. Complexation of cations follows a multistep reaction. For valinomycin the rate‐limiting step of cation complexation is a ligand conformational change which occurs during the stepwise substitution of solvent molecules from the cation.