The description of membrane lipid conformation, order and dynamics by 2H-NMR

Free radical recycling and intramembrane mobility in the antioxidant properties of alpha-tocopherol and alpha-tocotrienol.

Vitamin E (α-tocopherol) is essential for the prevention of photo-oxidative deterioration of biomembranes. The occurrence, relative biological activity and distribution of tocopherols in photosynthetic membranes is considered together with the possible biochemical and biophysical mechanisms by which tocopherols confer protection upon illuminated membranes. The common protective effects of Vitamin E in photo-synthetic membranes and in medically important light-induced diseases and conditions of the skin and eye in animal cell membranes are discussed. The importance of the Vitamin E-Vitamin C thylakoid antioxidant system is also examined, in terms of susceptibility to photo-oxidative damage under stress conditions including chilling, ageing and senescence, drought, atmospheric pollutants, herbicides and photosensitizing fungal toxins.

The antioxidant effects of thylakoid Vitamin E (α-tocopherol)

Lipid droplets (LDs) are ubiquitous dynamic organelles that store and supply lipids in all eukaryotic and some prokaryotic cells for energy metabolism, membrane synthesis, and production of essential lipid-derived molecules. Interest in the organelle's cell biology has exponentially increased over the last decade due to the link between LDs and prevalent human diseases and the discovery of new and unexpected functions of LDs. As a result, there has been significant recent progress toward understanding where and how LDs are formed, and the specific lipid pathways that coordinate LD biogenesis.

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Biogenesis of the multifunctional lipid droplet: lipids, proteins, and sites

The effect of sterols from mammals, plants, fungi, and bacteria on model and natural membrane dynamics are reviewed, in the frame of ordering-disordering properties of membranes. It is shown that all sterols share a common property: the ability to regulate dynamics in order to maintain membranes in a microfluid state where it can convey important biological processes. Depending on the sterol class, this property is modulated by molecular modifications that have occurred during evolution. The role of sterols in rafts, antibiotic complexes, and in protecting membranes from the destructive action of amphipathic toxins is also discussed.

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Sterols and membrane dynamics

The effects of 5, 10, and 20 mol % incorporation of alpha-tocopherol (vitamin E) on 50 wt % aqueous multilamellar dispersions of sn-2-substituted [2H31]palmitoylphosphatidylcholine (PC-d31), a saturated, deuterated phospholipid prepared from egg lysophosphatidylcholine, have been studied by deuterium nuclear magnetic resonance (2H NMR) and differential scanning calorimetry (DSC). Moment analysis of the 2H NMR spectra as a function of temperature and DSC heating curves demonstrate that the main gel to liquid-crystalline phase transition is progressively broadened and its onset temperature lowered by increasing concentrations of alpha-tocopherol. Below the transition temperature (40 degrees C) for PC-d31 bilayers, the 2H NMR spectra indicate that acyl chain motion is increased by addition of alpha-tocopherol and that this effect extends to lower temperatures with higher alpha-tocopherol content. Above the transition, average carbon-deuterium bond order parameters calculated from the first spectral moment establish that alpha-tocopherol increases acyl chain ordering within the PC-d31 bilayer by as much as 17% at 20 mol % incorporation. Profiles of order parameter vs. chain position, constructed from 2H NMR spectra following application of the depaking technique, show that despite higher order the general form of the profile is not significantly altered by alpha-tocopherol.

Deuterium NMR study of the interaction of alpha-tocopherol with a phospholipid model membrane.

Deuterium nuclear magnetic resonance (2H NMR) experiments have been performed on selectively deuterated cholesteryl palmitate (CP) and cholesteryl stearate (CS) in egg phosphatidylcholine (PC) unilamellar vesicles Egg PC vesicles were found to incorporate up to 5 mol % ester and to have a mean diameter of 22 nm Addition of 20 mol % cholesterol decreased the solubility of cholesteryl ester in the bilayer to approximately 2-3 mol %, but the vesicle size remained unchanged The 2H MNR results reveal that the acyl chains of CP and CS are highly disordered (SCD less than 010) both in the presence and in the absence of cholesterol T1 measurements for selectively deuterated CP and CS in egg PC vesicles indicate that the high degree of disorder of the ester molecule is not associated with an increase in the rate of gauche-trans chain isomerization Possible explanations for the low order parameters in terms of molecular motions and orientations are offered

Deuterium magnetic resonance of selectively deuterated cholesteryl esters in phosphatidylcholine vesicles.

The ternary systems EYL:H2O (50:50 wt %) containing 1 and 5 mol % cholesteryl palmitate-d31 or 1 and 5 mol % cholesteryl palmitate-16,16,16,16-d3 have been studied. Cholesteryl palmitate-d31 gave a unique deuterium magnetic resonance spectrum corresponding to a homogeneous (delta vQ = 3 and 12 kHz) and a solid phase (deltaVQ = 38 and 118 kHz). From the characteristic spectra and spin-lattice relaxation times, a procedure for calculating the amount of each phase present in the ternary mixture is given resulting in a maximum value of homogeneously dissolved cholesteryl palmitate of 0.2 +/- 0.1 mol % and a solid fraction above 0.2 mol %. The most probable order parameter for the (-CD2)n portion of the homogeneous fraction of cholesteryl palmitate-d31 was determined from the quadrupolar splittings to be S = 0.1 which is less than one-half that of the order parameter found for the lecithin chains. Possible explanations for the diminution of the order parameter for cholesteryl ester in bilayers are discussed.

Heiner Gorrissen

Papers

Deuterium NMR study of the interaction of alpha-tocopherol with a phospholipid model membrane.

Deuterium magnetic resonance of selectively deuterated cholesteryl esters in phosphatidylcholine vesicles.

Deuterium magnetic resonance study of cholesteryl esters in membranes.

Deuterium NMR study of the effect of n-alkanol anesthetics on a model membrane system.

Deuterium magnetic resonance of selectively deuterated cholesteryl esters in dipalmitoyl phosphatidylcholine dispersions