Application of Nuclear Magnetic Resonance to the Conformational Changes in Valinomycin during Complexation

Abstract

Alkali ion complex formation by the cyclic depsipeptide, valinomycin, has been studied by means of nuclear magnetic resonance spectroscopy. Characteristic perturbations of the positions and fine structures of the resonances of the protons of specific groups were observed upon complextion of the valinomycin with KCNS and CsCNS in CDCI3. Small amounts of water did not affect the structure of the complexes as judged by nuclear magnetic resonance spectral criteria. Preliminary studies were carried out on the rates of complexation and decomplexation using the broadening of the lactate methyl proton resonances. A measurable rate of transfer of the complexed cation between valinomycin molecules in 80% CH3OH, 20% CDCl3, was observed while no measurable exchange rate was observed in pure CDCl3. These results are consistent with valinomycin functioning as a mobile ion carrier in biological membrane systems.