EVIDENCE FOR A 2-DIMENSIONAL MOLECULAR LATTICE IN SUBGEL PHASE DPPC BILAYERS

Using a combination of X-ray diffraction data from oriented films and multilamellar liposomes of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylch oline (DPPC) in the subgel phase, we have established the presence of a 2D molecular lattice containing two lipid molecules. The proposed 2D lattice is consistent with all the X-ray diffraction data on the subg el phase of DPPC available in the literature. In this phase, the DPPC molecules are ordered in the plane of the bilayer and are also found t o be positionally correlated across a single bilayer but not with thos e in adjacent bilayers. We also present the possible molecular arrange ments for the proposed lattice.