Fluid phase structure of EPC and DMPC bilayers

X-ray diffraction data taken at high instrumental resolution were obtained for EPC and DMPC under various osmotic pressures, primarily at T = 30 degrees C. The headgroup thickness D-HH was obtained from relative electron density profiles. By using volumetric results and by comparing to gel phase DPPC we obtain areas A(EPC)(F) = 69.4 +/- 1.1 Angstrom(2) and A(DMPC)(F) = 59.7 +/- 0.2 Angstrom(2). The analysis also gives estimates for the areal compressibility K-A. The A(F) results lead to other structural results regarding membrane thickness and associated waters. Using the recently determined absolute electrons density profile of DPPC, the AF results also lead to absolute electron density profiles and absolute continuous transforms \F(q)\ for EPC and DMPC, Limited measurements of temperature dependence show directly that fluctuations increase with increasing temperature and that a small decrease in bending modulus K-c accounts for the increased water spacing reported by Simon et al. (1995) Biophys. J. 69, 1473-1483. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.