Rotational diffusion of band 3 in the red cell membrane: measurements using triplet probes

Rotational diffusion of band 3 in the human erythrocyte membrane has been investigated using the technique of flash photolysis. Membranes are labeled with the triplet probe eosin isothiocyanate; most of the label is found to be associated with band 3. Rotation is measured by observing the decay of dichroism of flash-induced absorbance changes arising from the eosin probe. The results indicate that band 3 rotates about an axis normal to the plane of the membrane with a diffusion coefficient in the order of 1,000 sec-1. Removal of spectrin has no observable effect on the rotation of band 3 at pH 7.6. Essentially similar results are obtained with a different probe, iodoacetamidoeosin. Both eosin derivatives are strong inhibitors of anion transport. Illumination of eosin-labeled ghosts causes a rapid loss of acetylcholinesterase activity but this can be prevented by prior displacement of oxygen in the sample by argon.