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

D H Haynes,A Kowalsky,B C Pressman

doi:10.1016/s0021-9258(18)94458-3

D H Haynes, A Kowalsky + Show 1 more

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https://doi.org/10.1016/s0021-9258(18)94458-3

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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.

Highlights

The concentration of valinomycin was varied between 110 mu and 13.7 mM in CDC& and no change in the position and fine structure was observed in the NMR spectrum
Additional evidence for the lack of polymerization was the absence of any spectral indication for intermediates during a titration of valinomycin with KCNS in CDC&
Since the channel mechanism of ionophore activity would be most consistent with the valinomycin molecule complexing a hydrated K+ rather than an unhydrated ion when water is available for hydration, NMR experiments were done in which water was deliberately added to CDCl, solutions of the KCNSvalinomycin complex

Summary

Introduction

Since the channel mechanism of ionophore activity would be most consistent with the valinomycin molecule complexing a hydrated K+ rather than an unhydrated ion when water is available for hydration, NMR experiments were done in which water was deliberately added to CDCl, solutions of the KCNSvalinomycin complex. The concentration of valinomycin was varied between 110 mu and 13.7 mM in CDC& and no change in the position and fine structure was observed in the NMR spectrum. Additional evidence for the lack of polymerization was the absence of any spectral indication for intermediates during a titration of valinomycin with KCNS in CDC& (i.e. the spectrum obtained during titration was identical with the one which obtains when the spectra of the complexed and uncomplexed molecule are added, with the appropriate amplitude ratio).

Results

Conclusion