ABSTRACT
The diffusion of phospholipids across the membrane has a very low probability because of the large free energy change required to move the head group through the hydrophobic region. Many fundamental processes in cells require motions of membrane components. A principal stimulus for the interest in lateral motion of membrane components came from the work of L. D. Frye and M. Edidin in 1970, who inferred lateral processes from cell fusion data. Diffusion of lipids was found to be the same on the “smooth” regions as on the microvillous regions of mouse egg surfaces. Spectral analysis, especially of line widths and line shapes, provides information not only on lateral diffusion but on other dynamics, especially rotation. Studies of lipid lateral diffusion are rapidly evolving from a stance in which the rates themselves were of interest to a stance in which the measurements are being used to solve other questions regarding the cell membrane.
