EFFECT OF PRESSURE ON THE DIMYRISTOYLPHOSPHATIDYLCHOLINE BILAYER MAINTRANSITION

Deuterium nuclear magnetic resonance was used to study the effect of p ressure on the liquid crystal to gel phase transition in multilamellar vesicles of chain perdeuterated dimyristoylphosphatidylcholine (DMPC- d(54)). The first spectral moment (M-1), which is proportional to the mean orientational order parameter for the DMPC-d(54) acyl chain, was measured as a function of temperature at ambient pressure and at 160 M Pa and as a function of pressure at 25 degrees C, 35 degrees C, and 45 degrees C. Application of hydrostatic pressure was found to increase the magnitude of the jump in M-1 at the transition and to reduce the s ensitivity of M-1 to temperature just above the transition. These obse rvations suggest that the separation between the observed first-order transition and the critical point for phospholipid bilayers increases with increasing pressure.