Dmitri P. Kharakoz
Inst. of Theoret. and Exp. Biophys., Russian Acad. Sci., 142292 Pushchino, Moscow, Russia
This paper reviews phase transitions in the lipid membranes and protein molecules studied by means of ultrasonic (sound velocity and absorption) and related methods (calorimetric, volumetric, and others). Peculiarities of phase transitions in small-dimension systems in an aqueous environment (a finite width of the transition zone, probability of critical nuclei formation, hysteresis, hydration changes, etc.) are discussed. A comparison of ultrasonic and calorimetric methods showing their complementarity in the studies of kinetics of phase transitions is presented. Ultrasonic data on the melting of lipid vesicles in aqueous dispersions are reviewed. Recent achievements in the ultrasonic study of the kinetic mechanism of creation and growth of gel nuclei within the parent liquid-crystalline phase are reported. Ultrasonic studies of the protein/lipid interactions are reviewed and perspectives are outlined. Native to molten globule state transition in globular proteins is considered (volume and compressibility changes, acoustic relaxation, protein interior hydration). The differences in the behavior of the phase transitions in membranes and in protein molecules are discussed. New questions for further ultrasonic studies of the phase transitions are formulated.