Rotational diffusion of membrane proteins: measurements with bacteriorhodopsin, band-3 proteins and erythrocyte oligosaccharides.

Rotational diffusion of membrane proteins may be measured by detecting flash-induced transient dichroism of triplet probes or intrinsic chromophores. The method is illustrated by the following applications. 1. Anisotropy decay curves have been measured for bacteriorhodopsin incorporated into lipid vesicles. The data are used to critically test a theoretical model in which it is assumed that protein rotation occurs only around the membrane normal. 2. Rotational diffusion of eosin-labelled band-3 proteins in the human erythrocyte membrane has been investigated. The measurements illustrate the value of protein rotation measurements for studying protein-protein associations in membranes. In particular, it is shown that up to 40% of band-3 protein has a restricted mobility at 37 degrees C due to interaction with the erythrocyte cytoskeleton. 3. Oligosaccharide chains on the surface of human erythrocytes have been labelled with eosin-TSC. The motion of these chains has been investigated by combining transient dichroism studies in the microsecond time range with picosecond fluorescent depolarization measurements.