Redetermination of the pressure dependence of the lipid bilayer phase transition

Abstract

The effect of pressure on the phase transition temperature for the dipalmitoyllecithin bilayer was redetermined by following the volume change accompanying the transition. These measurements were carried out isothermally with the transition from the ordered to the disordered phase induced by decreasing the pressure. This contrasts with previous measurements which were carried out at constant pressure and increasing temperature. The transition at every temperature was sharp and confirmed the previous observation that the volume change associated with the transition (0.033 ml g-1) is invariant with pressure. The present measurements, in contrast to the previous results, indicate that dPm/dTm at all pressures is in agreement with the 1 atm value of .DELTA.H/Tm.DELTA.V within experimental error where Tm and Pm are the temperature and pressure of the phase transition, respectively. These results, which are now in agreement with all other known pressure data, indicate that the entropy change associated with the transition is invariant with pressure.