19F-Nuclear magnetic resonance of fluorine-labeled fatty acids in phospholipid bilayer vesicles

Abstract

19F-labeled fatty acids, labeled at the 4, 6, 9, 12 and terminal positions, and intercalated into dimyristoylphosphatidylcholine (DMPC) small unilamellar vesicles were studied using 19F-NMR as a function of temperature and perturbant incorporation. The perturbants studied were cholesterol, gramicidin A and polylysine. It was found that the fluorines give rise to a single resonance whose line width decreases substantially with increasing temperature and increases as the fluorine is positioned from the chain terminus toward the polar head group, peaking at the 6 position. When cholesterol is incorporated into the phospholipid vesicles, the fluorine resonance line widths increase dramatically and uniformly along the chain at all temperatures. Gramicidin A incorporation leads to a similar though smaller increase in line widths which, in contrast, diminish with increasing temperatures. On the other hand polylysine interactions lead to little change in the line width of the fluorine-substituted fatty acids. Incorporation of cholesterol increases the size of the phospholipid vesicles but the other perturbants do not, as determined by gel-permeation chromatography. These results are consistent with what is known about the changes in phospholipid bilayer structure brought about by the incorporation of these substances and indicate that 19F-NMR of fluorine-substituted fatty acids intercalated in lipid bilayers can extend our knowledge of model membrane systems.