PACKING CHARACTERISTICS OF 2-COMPONENT BILAYERS COMPOSED OF ESTER-LINKED AND ETHER-LINKED PHOSPHOLIPIDS

The miscibility properties of ether- and ester-linked phospholipids in two-component, fully hydrated bilayers have been studied by different ial scanning calorimetry (DSC) and Raman spectroscopy, Mixtures of 1,2 -di-O-hexadecyl-rac-glycero-3-phosphocholine (DHPC) with 1,2-dipalmito yl-sn-glycero-3-phosphoethanolamine (DPPE) and of 1,2-dipalmitoyl-sn-g lycero-3-phosphocholine (DPPC) with ,2-di-O-hexadecyl-sn-glycero-3-pho sphoethanolamine (DHPE) have been investigated. The phase diagram for the DPPC/DHPE mixtures indicates that these two phospholipids are misc ible in all proportions in the nonrippled bilayer gel phase. In contra st, the DHPC/DPPE mixtures display two regions of gel phase immiscibil ity between 10 and 30 mol% DPPE, Raman spectroscopic measurements of D HPC/DPPE mixtures in the C-H stretching mode region suggest that this immiscibility arises from the formation of DHPC-rich interdigitated ge l phase domains with strong lateral chain packing interactions at temp eratures below 27 degrees C, However, in the absence of interdigitatio n, our findings, and those of others, lead to the conclusion that the miscibility properties of mixtures of ether- and ester-linked phosphol ipids are determined by the nature of the phospholipid headgroups and are independent of the character of the hydrocarbon chain linkages. Th us it seems unlikely that the ether linkage has any significant effect on the miscibility properties of phospholipids in biological membrane s.