The effect of gramicidin A on phospholipid bilayers

The helical polypeptide, gramicidin A has been widely studied as a model for the interactions of hydrophobic proteins with lipid bilayer membranes. Many reports are now available of the physical effects of mixing gramicidin A with phospholipid membranes, however, the interpretation of these data remains unclear. The purpose of this communication is to examine the controversial claim that high concentrations of gramicidin A' cause disorder within the L alpha phase of phosphatidylcholine-water dispersions. Solid-state nuclear magnetic resonance (NMR), density gradient and X-ray diffraction techniques are used to confirm the existence of such an effect and mechanisms are discussed which account for the known effects of gramicidin A on lipid bilayers.