Structure and thermotropic properties of hydrated 1-eicosyl-2-dodecyl-rac-glycero-3-phosphocholine and 1-dodecyl-2-eicosyl-rac-glycero-3-phosphocholine bilayer membranes
The ether-linked phosphatidylcholines 1-eicosyl-2-dodecyl-rac-glycero-3-phosphocholine (EDPC) and 1-dodecyl-2-eicosyl-rac-glycero-3-phosphocholine (DEPC) have been investigated by differential scanning calorimetry (DSC) and X-ray diffraction. DSC of hydrated EDPC shows a single endothermic transition at 34.8 /sup 0/C after storage at -4 /sup 0/C while DEPC shows three endothermic transitions at 7.7 and approx.9.0/sup 0/ and a 25.2 /sup 0/C. Both the single transition of EDPC and the two higher temperature transitions of DEPC are reversible, while the approx.7.7 /sup 0/C transition of DEPC increases in enthalpy on low-temperature incubation. At 23 /sup 0/C, X-ray diffraction of hydrated EDPC shows a sharp reflection at 4.2 A together with lamellar with reflections corresponding to a bilayer periodicity. Electron density profiles derived from swelling experiments show a phosphate-phosphate intrabilayer distance of 36 A at all hydrations. This, together with calculated lipid thickness and molecular area considerations, suggests an interdigitated, three chains per head group, bilayer gel phase with no hydrocarbon chain tilt. This is structurally analogous to the bilayer gel phase of hydrated 18:0/10:0 ester PC. The ability of both EDPC and DEPC to form triple-chain interdigitated gel-state bilayers suggests that the conformational inequivalence at the sn-1 and sn-2 positions is less pronounced in the ether-linked PCs compared to the ester-linked PCs, where only one of the positional isomers, e.g., 18:0/10:0 but not 10:0/18:0 PC, forms the triple-chain structure. Thus, a different conformation around the glycerol is predicted for ether-linked PC compared to ester-linked PC.
- Research Organization:
- Boston Univ. of School of Medicine, MA
- OSTI ID:
- 6792960
- Journal Information:
- Biochemistry; (United States), Vol. 26:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
PHOSPHOLIPIDS
CALORIMETRY
MOLECULAR STRUCTURE
X-RAY DIFFRACTION
CHOLINE
CONFORMATIONAL CHANGES
MEMBRANES
ALCOHOLS
AMINES
AMMONIUM COMPOUNDS
COHERENT SCATTERING
DIFFRACTION
DRUGS
ESTERS
HYDROXY COMPOUNDS
LIPIDS
LIPOTROPIC FACTORS
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
QUATERNARY COMPOUNDS
SCATTERING
550201* - Biochemistry- Tracer Techniques