ULTRASONIC MEASUREMENT OF LIPID BILAYER TRANSITION IN THE PRESENCE OF MELITTIN

Ultrasonic relaxation was measured for suspensions of sonicated dimyristoyl phosphatidylcholine (DMPC) vesicles in the presence of melittin, the lipid/melittin ratio being 100/1. The results showed that a DMPC/melittin suspension at pH 5 was characterized by much larger relaxation strength and relaxation time than a pure DMPC vesicle suspension. The relaxation phenomenon indicated anomalous enhancement in the vicinity of a gel-to-liquid crystal transition point, which was the characteristic feature of a critical phenomenon. The transition temperature increased by about 1-degrees-C with the addition of melittin.