The action of a carbonsuboxide dimerized gramicidin A on lipid bilayer membranes

Gramicidin A was dimerized with carbonsuboxide as bifunctional reagent. The effect of the resulting malonyl-bis-desformylgramicidin on lipid bilayer membranes was investigated and compared with the effect of the monomer gramicidin. It was found that the single channel conductance and the ion selectivity are very similar to the behaviour of the monomer molecule, whereas the channel forming kinetics and the life time of the single channel of the malonyl-bis-desformylgramicidin differ strongly from the behaviour of the monomer gramicidin. The electrical relaxations are very small and possibly associated with some structural changes of the membrane after a voltage jump. The single channel lifetime of the malonyl-bis-desformylgramicidin is measured in minutes, whereas for the same lipid system the single channel lifetime in the case of the monomer gramicidin is restricted to 1-2 s. It is concluded that the malonyl-bis-desformylgramicidin-molecule itself (as a single molecule) forms an ionic channel without further association.