Stability of sodium and potassium complexes of valinomycin

• Published in: Biochimica et biophysica acta. General subjects Vol. 372; no. 2; pp. 426 - 435
• Main Authors: Rose, Mary Callaghan, Henkens, Robert W.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.1974
• ISSN: 0304-4165; 1872-8006
• DOI: 10.1016/0304-4165(74)90204-9

Stability constants of sodium and potassium complexes of valinomycin in some alcohols and water—organic solvent mixtures have been determined by titration, using circular dichroism to monitor complex formation. Constants range from 10 1 to 10 6 M −1. Stability of the potassium and sodium complexes increases with decreasing dielectric constant, but the ratio of the constants remains about 10 3–10 4. As others have shown, a similar selectivity for K + is observed in a number of other types of measurements involving valinomycin. These include the permeability and conductance ratios which characterize the selectivity of cation transport through membranes and the ratio of salt extraction equilibrium constants. On the basis of data presented here, and elsewhere, it is suggested that conformational constraints within the depsipeptide part of the complexes aid ion selectivity and that differences in cation solvation and carbonyl ligand binding energies make an important, roughly equal, contribution.