Membrane curvature, lipid segregation, and structural transitions for phospholipids under dual-solvent stress

Journal Article · Tue Jan 09 04:00:00 EST 1990 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00453a010· OSTI ID:7008608

Rand, R P; Fuller, N L ^[1]; Gruner, S M ^[2]; Parsegian, V A ^[3]

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1. Brock Univ., St. Catharines, Ontario (Canada)
2. Princeton Univ., NJ (USA)
3. National Institutes of Health, Bethesda, MD (USA)

Amphiphiles respond both to polar and to nonpolar solvents. In this paper X-ray diffraction and osmotic stress have been used to examine the phase behavior, the structural dimensions, and the work of deforming the monolayer-lined aqueous cavities formed by mixtures of dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC) as a function of the concentration of two solvents, water and tetradecane (td). In the absence of td, most PE/PC mixtures show only lamellar phases in excess water; all of these become single reverse hexagonal (H{sub II}) phases with addition of excess td. The spontaneous radius of curvature R{sub 0} of lipid monolayers, as expressed in these H{sub II} phases, is allowed by the relief of hydrocarbon chain stress by td; R{sub 0} increases with the ratio DOPC/DOPE. Single H{sub II} phases stressed by limited water or td show several responses. (a) the molecular area is compressed at the polar end of the molecule and expanded at the hydrocarbon ends. (b) For circularly symmetrical water cylinders, the degrees of hydrocarbon chain splaying and polar group compression are different for molecules aligned in different directions around the water cylinder. (c) A pivotal position exists along the length of the phospholipid molecule where little area change occurs as the monolayer is bent to increasing curvatures. (d) By defining R{sub 0} at the pivotal position, the authors find that measured energies are well fit by a quadratic bending energy. (e) For lipid mixtures, enforced deviation of the H{sub II} monolayer from R{sub 0} is sufficiently powerful to cause demixing of the phospholipids in a way suggesting that the DOPE/DOPC ratio self-adjusts so that its R{sub 0} matches the amount of td or water available, i.e., that curvature energy is minimized.

• OSTI ID: 7008608
• Journal Information: Biochemistry; (USA), Journal Name: Biochemistry; (USA) Vol. 29:1; ISSN 0006-2960; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550602* -- Medicine-- External Radiation in Diagnostics-- (1980-)
62 RADIOLOGY AND NUCLEAR MEDICINE
COHERENT SCATTERING
DIFFRACTION
DIFFUSION
ESTERS
LIPIDS
MEMBRANES
MOLECULAR STRUCTURE
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
OSMOSIS
PHOSPHOLIPIDS
SCATTERING
STRUCTURAL CHEMICAL ANALYSIS
X-RAY DIFFRACTION