¹Department of Physics, Laboratory of Molecular Biophysics and Medical Physics, „Alexandru Ioan Cuza” University, Iasi, Romania
²Interdisciplinary Research Department – Field Science, „Alexandru Ioan Cuza” University , Iasi, Romania

Antimicrobial peptides (AMPs) are known to be the effector molecules of innate immune system and they selectively disrupt the integrity of bacterial membrane by pore formation. The complex phenomena of the interactions between the antimicrobial peptides and different lipid systems are only partially understood. Herein, we employed spectrofluorometry to unravel the effects exerted by phloretin and potasium chloride ionic strength upon adsorption and insertion of mellitin, which is the major toxic component in the venom of the european honey bee Apis mellifera.^[1] As known, phloretin molecules alter the electrical properties and the permeability of membranes as a result of its adsorption to the surface of the lipid monolayer, by causing a decrease in the membrane dipole potential ^[2], whereas potasium chloride interferes with the membrane adsorbtion and insertion of the peptide monomers, via a screening effect which takes place at the water-lipid interface^[3].

Informations about the degree of peptide adsorbtion in the liposome membrane were obtained from the decrease in the tryptophan fluorescence intensity, in the presence of the acrylamide quencher. Insertion and the kinetics of transmembrane pore formation by mellitin were monitored through the calcein release assay from small unilamellar vesicles (SUVs). Our data indicate that the presence of the phloretin enhances the adsorbtion and insertion of mellitin monomers at the membrane interface and that at a high ionic strength, the accessibility of peptides to the lipid membrane interface is dimished.