ULTRASONIC STUDY OF MELITTIN EFFECTS ON PHOSPHOLIPID MODEL MEMBRANES

Low dose effects of melittin on dilute suspensions of dipalmitoylphosp hatidylcholine multilamellar vesicles are investigated by studying the acoustic properties of the system. The temperature dependencies of so und velocity and absorption have been measured at 7.2 MHz in the tempe rature range of 20-55-degrees-C, for different peptide/lipid molar rat ios, R. The most pronounced effects were observed at R = 5 x 10(-3), i n the vicinity of the pretransition, with a simultaneous increase in s ound absorption and velocity. This indicates that melittin affects the polar head group region of the bilayer resulting in a decrease in mob ility of the polar head groups. A nonmonotonic dependence of the main transition temperature, with an initial decrease followed by an increa se as melittin is added, is interpreted as a consequence of a destabil izing action of the interfaces between melittin-affected clusters and the unaffected phase.