Fluorescence energy transfer on erythrocyte membranes

Stationary and time-dependent fluorescence were measured for a donor/ acceptor (DA) pair bound to membrane proteins of bovine erythrocyte ghosts. The donor N-(p-(2-benzoxazolyl)phenyl)-maleimide (BMI) and the acceptor fluram bind to SH- and NH2-residues, respectively. The fluorescence spectra and the time-dependent emission were consistent with radiationless fluorescence energy transfer (RET). Band3 protein is the only membrane spanning protein with accessible SH-groups for the coupling of BMI molecules, and therefore only acceptor binding sites on the same band3 protein were counted by the RET measurements performed. A density of RET-effective acceptor binding sites c = 0.072 nm-2 was calculated on the basis of the two-dimensional Förster-kinetics.