CD and fluorescence were used to study the interaction of the model peptide melittin with dimyristoylphosphatidylcholine (DMPC) bilayer liposomes. Melittin binds tightly to the lipid membrane and undergoes a conformational change from a random to an .apprx.70% a-helical structure in the membrane-bound state. This binding is influenced by the phys. state of the membrane, the binding const. being higher in the fluid than in the ordered membrane phase. Tryptophan-19 of melittin which is positioned in the region of the glycerol backbone of DMPC, has a lower solvent accessibility in the membrane as compared to that in aq. soln. At temps. above the lipid phase transition the tryptophan residue is buried deeper within the membrane and is in a more hydrophobic microenvironment. [on SciFinder (R)]