Gramicidin conducting dimers in lipid bilayers are stabilized by single-file ionic flux along them.
Gramicidin D was incorporated in a biomimetic membrane consisting of a lipid bilayer tethered to a mercury electrode via a hydrophilic spacer, and its behavior was investigated in aqueous 0.1 M KCl by potential-step chronocoulometry and electrochemical impedance spectroscopy. The impedance spectra, recorded from 0.1 to 1 x 10(5) Hz over a potential range of 0.7 V, were fitted to a series of RC meshes, which were related to the different substructural elements of the biomimetic membrane. These impedance spectra were compared with those obtained by incorporating valinomycin, under otherwise identical conditions. The potential dependence of the stationary currents reported on bilayer lipid membranes by Bamberg and Läuger (Bamberg, E.; Läuger, P. J. Membrane Biol. 1973, 11, 177-194) as well as those extracted from potential-step chronocoulometric measurements was interpreted by relating the increase in gramicidin dimerization to a progressive increase in single-file K+ flux along the dimeric channels. An analogous approach was adopted in explaining the difference between the impedance spectra obtained with gramicidin D and those obtained with valinomycin. It is concluded that gramicidin has a low tendency to form dimers in the absence of ionic flux.
Department of Chemistry, Florence University, via della Lastruccia 3, 50019 Sesto Fiorentino (Firenze), Italy.
Lucia
L
Becucci
Alessandra
A
Santucci
Rolando
R
Guidelli
D000465:Algorithms; D032701:Biomimetics; D004563:Electrochemistry; D006096:Gramicidin / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008670:Metals / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry; D011189:Potassium Chloride / Q000737:chemistry; D013057:Spectrum Analysis; D014634:Valinomycin / Q000737:chemistry
D008051:Lipid Bilayers; D008670:Metals; D010713:Phosphatidylcholines; D006096:Gramicidin; D014634:Valinomycin; C021016:1,2-diphytanoylphosphatidylcholine; D011189:Potassium Chloride