Raman spectroscopic studies of the packing properties of mixed dihexadecyl- and dipalmitoylphosphatidylcholine bilayer dispersions.
X-ray diffraction studies suggest the existence of two separate gel phases for mixed dihexadecylphosphatidylcholine (DHPC)/dipalmitoylphosphatidylcholine (DPPC) bilayers [Kim, J. T., Mattai, J., & Shipley, G. G. (1987) Biochemistry 26, 6599-6603; Lohner, K., Schuster, A., Degovics, G., Müller, K., & Laggner, P. (1987) Chem. Phys. Lipids 44, 61-70]. In one gel phase the lipid chains are interdigitated, while the other gel phase exhibits the conventional bilayer form. We use Raman spectroscopy to provide a detailed molecular analysis of the intermolecular and intramolecular interactions of the DHPC and DPPC molecules within these mixed bilayers. Observation of the methylene chain C-H stretching modes of DHPC and the methylene chain C-D stretching modes of DPPC-d62 for various mixed DHPC/DPPC-d62 bilayers enables the packing characteristics and conformational order of each lipid to be monitored separately. The spectral data indicate that the packing properties of DPPC-d62 in the mixed-lipid bilayers remain relatively unchanged, while the intramolecular and intermolecular properties of DHPC change dramatically as a function of the composition of the DHPC/DPPC-d62 mixed bilayer. This is consistent with a model based upon the existence of three characteristic lipid types for the mixed-lipid system, namely, domains of pure DPPC-d62 and pure DHPC species with interface lipids or boundary regions between the bulk domains.
Devlin
M T
MT
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
Levin
I W
IW
D015060:1,2-Dipalmitoylphosphatidylcholine; D008051:Lipid Bilayers / Q000032:analysis*; D010742:Phospholipid Ethers; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman; D013696:Temperature
C052298:1,2-dihexadecyl-sn-glycero-3-phosphocholine; D008051:Lipid Bilayers; D010742:Phospholipid Ethers; D015060:1,2-Dipalmitoylphosphatidylcholine