Vertical Fluctuations of Phospholipid Acyl Chains in Bilayers

The possibility of vertical displacement of acyl chains in lipid bilayers has been examined by quenching the fluorescence of 2-(9-anthroyloxy)palmitic acid with 5- and 16-doxylstearates in dipalmitoylphosphatidylcholine unilamellar vesicles. Measurement of lifetime and steady-state quenching showed that the dynamic component of quenching was independent of the transverse position of the quencher indicating that a quencher at the 16-position could interact with a fluorophore at the 2-position with high frequency. The differences in steady-state quenching could be accounted for by the differences in the static component of quenching. The results provide further evidence for rapid vertical displacements of acyl chains in phospholipid bilayers.