Rotational and translational diffusion in membranes measured by fluorescence and phosphorescence methods.

A lipid bilayer provides a compartmentalized matrix within which embedded proteins and other macromolecules are in constant states of motion and redistribution—the processes that are essential to cellular mechanisms, such as metabolism, endocytosis and secretion, differentiation, locomotion, and signal transduction. A lipid bilayer in natural and reconstituted membranes imposes constraints that restrict the larger segmental and global motions of constituent molecules to the microsecond to millisecond time domains. This chapter discusses methods for analyzing such rotational and translation displacements based on the time-resolved emission of light in the form of fluorescence and phosphorescence. These techniques offer the sensitivity and selectivity required for the studies of relatively sparse cell-surface receptors or other membrane components in preparations examined in a microscope and in a suspension