Surface curvature and mobility in phospholipid bilayers. NMR studies of lecithin-deoxycholate mixed micelles

In mixed micelles of phospholipids and bile salts, the phospholipids are arranged as a flat bilayer with bile salts distributed along the hydrophobic edges. The linewidths of signals in the proton magnetic resonance spectra of such mixed micelles depend strongly on the size of the micelles, which is a function of the molar ratio of the components. The signals in the spectra of such mixed micelles are much broader than the corresponding signals in the much larger, curved bilayers of lecithin vesicles obtained by ultrasonic irradiation. This result strongly supports the idea that curvature is a prime factor in determining proton NMR linewidths, probably through a disruptive effect of curvature on the molecular packing in phospholipid bilayers.