Transient dichroism measurements of rotational diffusion and interactions of proteins in erythrocyte membranes

Abstract

Flash-induced transient dichroism of triplet probes or extrinsic chromophores has been extensively employed to measure rotational diffusion of proteins embedded in biological membranes. In human erythrocyte membranes the anion transport protein, band 3, may be selectively labelled with eosin-5-maleimide. This has permitted a detailed study to be made of the rotational dynamics of band 3 using the transient dichroism method. In recent experiments the interaction of the bee venom polypeptide, melittin, with erythrocyte membranes was investigated. Melittin causes a dramatic loss of rotational mobility of band 3, probably by electrostatic crosslinking of the protein into large relatively immobile aggregates. The concentration of melittin which produces this effect correlates with the concentration required for cell lysis. This suggests a possible role for melittin-protein interactions in the biological activity of the polypeptide.