Interaction of Gramicidin Derivatives with Phospholipid Monolayers

Abstract

A study of the interaction of gramicidin A (gA), tert-butyloxycarbonyl-gramicidin (g-BOC), and desformyl gramicidin (g-des) with dioleoyl phosphatidylcholine (DOPC) and DOPC/phosphatidylserine (PS) mixed monolayers on a mercury electrode is reported in this paper. Experiments were carried out in electrolytes KCl (0.1 mol dm(-3)) and Mg(NO3)2 (0.05 mol dm(-3)). The channel-forming properties of the gramicidins were studied by following the reduction of Tl(I) to Tl(Hg). The frequency dependence of the complex impedance of coated electrode surfaces in the presence and absence of the gramicidins was estimated between 65,000 and 0.1 Hz at potentials of -0.4 V versus Ag/AgCl with 3.5 mol dm(-3) KCl. Epifluorescence microscopy was used to qualitatively correlate the interaction of the gramicidin peptides with dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylglycerol (DPPG) at the air-water interface. gA was shown to form Tl+ conducting channels in a DOPC monolayer, while g-BOC and g-des did not. In DOPC-30% PS (DOPC-0.3PS) layers, there is a marked increase in channel activity of all three gramicidin derivatives. None of the peptides facilitate the permeability of the DOPC-0.3PS layer to Cd2+. All three peptides interact with the layer as shown by capacitance-potential curves and impedance spectroscopy indicated by penetration of the peptide into the dielectric, an increase in surface "roughness", and an increased significance of low-frequency relaxations. The order of interaction is gA> g-des > g-BOC. The epifluorescence study of DPPC and DPPG layers at the air-water interface shows a selective action of the different gramicidins.

Interaction of Bispyridinium Compounds with Phospholipid Layers in Presence and Absence of Electric Field

“…This is shown by a lower value of a which is very low at 0.54 where the DOPC is completely or partially replaced by MB408. In this case the b value which may relate to surface roughness is also significantly decreased [20,21,26,28]. The time constant (t) of the I À interaction is also increased when the compound is associated with the layer.…”

“…This was done using the EXCEL (Microsoft) spreadsheet. Curve fitting of the Im Y w À1 vs. w data was carried out using IGOR (Wavemetrics) as before [20,21] and the coefficients were used to generate the Re Y w À1 vs. w plots so that the fitted plots in the complex capacitance plane could be constructed. Due to the absence of any electroactive component, the simplest equivalent circuit model is the uncompensated solution resistance (R u ) of the cell and the capacitance (C) of the working electrode in series [24].…”

“…All potentials in this paper are quoted versus the potential of the above Ag/AgCl reference electrode. In the impedance-frequency measurements, a solution resistance of around 280 -300 ohms was recorded for the cell [20,21]. Diagnostic plots of the impedance data showed it to be that of an RC series circuit as before [20,21].…”

“…In the impedance-frequency measurements, a solution resistance of around 280 -300 ohms was recorded for the cell [20,21]. Diagnostic plots of the impedance data showed it to be that of an RC series circuit as before [20,21]. There was a distinct absence of instability at high frequencies and for this reason, the use of a fourth pseudoreference electrode was not considered necessary at this stage.…”

Fluorinated vs hydrogenated surfactants in mixtures with valinomycin—The Langmuir monolayer study

“…Contrary to other peptide antibiotics, like gramicidin A or alamethicin, which form conducting channels both in artificial and natural membranes [1][2][3], valinomycin is mainly known for its ionoforic activity, i.e. it complexes specifically potassium ions and carries them through biomembranes [4,5].…”