Role of the position of unsaturation on the phase behavior and intrinsic curvature of phosphatidylethanolamines.
The bilayer-to-hexagonal phase transition temperatures (T(H)) of di-18:1(C) phosphatidylethanolamine with double bonds at positions 6, 9, and 11 are 37 degrees C, 8 degrees C, and 28 degrees C, respectively, as measured by differential scanning calorimetry and x-ray diffraction. Thus T(H) exhibits a minimum when the C=C is around position 9, similar to what has been found for the gel-to-liquid crystalline phase transition temperature in other lipids. Factors that may contribute to the dependence of T(H) on double bond position were studied by x-ray diffraction of the hexagonal phases in the presence and absence of added alkane, with or without the osmotic stress of polyethylene glycol, and over a wide temperature range. The lattice dimensions show that the intrinsic radius of lipid monolayer curvature increases as the double bond is moved toward the tail ends. A measure of the bending moduli of these lipid monolayers shows a higher value for the 9 position, and lower values for the other two. Consideration of the bilayer-to-hexagonal transition in terms of bending and interstitial energies provides a rationale for the relative values of T(H).
Department of Biochemistry, McMaster University Health Sciences Centre, Hamilton, Ontario, Canada. epand@fhs.csu.mcmaster.ca
R M
RM
Epand
N
N
Fuller
R P
RP
Rand
D002152:Calorimetry, Differential Scanning; D005782:Gels; D008051:Lipid Bilayers; D008961:Models, Structural; D008968:Molecular Conformation; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014961:X-Ray Diffraction
D005782:Gels; D008051:Lipid Bilayers; D010714:Phosphatidylethanolamines