AMPHIPHILIC MODEL PEPTIDES - CIRCULAR-DICHROISM MEASUREMENTS AND INVESTIGATIONS BY A LANGMUIR BALANCE

The capability of amphiphilic oligopeptides carrying a hydrophobic alp ha-helical amino acid sequence to be integrated into the lipid bilayer of phospholipid liposomes was described in the first part of this wor k. Circular dichroism measurements in solution and after incorporation in liposomes showed a dependence on the length of the hydrophobic leu cine chain. The leucine chains preferred to adopt the conformation whi ch corresponds best to the length of the lipid bilayer: the longer pep tides were incorporated in the lipid bilayer as alpha-helices, while t he shorter ones changed to beta-sheet conformation. At the air/water i nterface the amphiphiles are able to orientate themselves in a monolay er adopting a beta-structure if they do not carry an artificial group. On the contrary amphiphiles with polyethyleneoxide headgroups are ori entated as alpha-helices vertically to the water surface. The volumino us polyethyleneoxide groups prevent a more compact packing and the tra nsition of the alpha-helix to an extended beta-sheet conformation. (C) 1996 Academic Press, Inc.