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Depth of bilayer penetration and effects on lipid mobility conferred by themembrane-active peptidesmagainin, melit-tin, and a hydrophobic helical sequence KKA(LA)7KK (denoted KAL), were investigated by colorimetric and time-resolved fluorescence techniques in biomimetic phos-pholipid/poly(diacetylene)vesicles. The experiments dem-onstrated that the extent of bilayer permeation and peptide localization within the membrane was dependent upon the bilayer composition, and that distinct dynamic modifica-tions were induced by each peptide within the head-group environment of the phospholipids | Eur. J. Biochem. 270 4478-4487 2003 FEBS 2003 doi 10.1046 j.1432-1033.2003.03840.x Bilayer localization of membrane-active peptides studied in biomimetic vesicles by visible and fluorescence spectroscopies Tanya Sheynis1 Jan Sykora2 Ales Benda2 Sofiya Kolusheva1 Martin Hof2 and Raz Jelinek1 1 Department of Chemistry and the Stadler Minerva Center for Mesoscopic Macromolecular Engineering Ben Gurion University of the Negev Beersheva Israel 2J. Heyrovsky Institute of Physical Chemistry Academy of Sciences of the Czech Republic and Center for Complex Molecular Systems and Biomolecules Prague the Czech Republic Depth of bilayer penetration and effects on lipid mobility conferred by the membrane-active peptides magainin melit-tin and a hydrophobic helical sequence KKA LA 7KK denoted KAL were investigated by colorimetric and time-resolved fluorescence techniques in biomimetic phos-pholipid poly diacetylene vesicles. The experiments demonstrated that the eetent of bilayer permeation and peptide localization within the membrane was dependent upon the bilayer composition and that distinct dynamic modifications were induced by each peptide within the head-group environment of the phospholipids. Solvent relaeation fluorescence correlation spectroscopy and fluorescence quenching analyses employing probes at different locations within the bilayer showed that magainin and melittin inserted close to the glycerol residues in bilayers incorporating negatively charged phospholipids but predominant association at the lipid-water interface occurred in bilayers containing zwitterionic phospholipids. The fluorescence and colorimetric analyses also eeposed the different permeation properties and distinct dynamic influence of the peptides magainin eehibited the most pronounced interfacial attachment onto the vesicles melittin penetrated more into the bilayers while the KAL peptide inserted deepest into the hydrophobic core of the lipid assemblies. The solvent relaeation results suggest .