Bilayer thickness from lipid-chain dynamics: Influece of cholesterol and electric charges. A 2H-NMR approach.

The bilayer hydrophobic thickness l is estimated from the 2H-NMR spectra of acyl chain perdeuteriated membrane phospholipids. Values obtained from individual quadrupolar splittings and those from the first moment of a powder spectrum are in close agreement. In the fluid (La) phase, the thermal variation of dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphatidic acid (DMPA) at pH 4.2 and 8.2, and DMPC: cholesterol (7:3) bilayer thicknesses are compared; 30% cholesterol increases the thickness of dMPC by approximately 4-5 Å, whatever the temperature. DMPC and DMPA (whatever the pH) have the same hydrophobic thickness near their respective Tc, the gel-to-fluid phase transition temperature, and display a very similar l decrease when increasing the temperature. However, at high temperatures (60°C) DMPC is thinner than DMPA by approximately 1 Å. Steric, electrostatic, and temperature constraints are therefore seen to modulate the biomembrane hydrophobic thickness , as easily estimated by 2H-NMR. [ABSTRACT FROM AUTHOR]