FLUORESCENCE ENERGY-TRANSFER ON ERYTHROCYTE-MEMBRANES

Stationary and time-dependent fluorescence were measured for a donor/a cceptor (DA) pair bound to membrane proteins of bovine erythrocyte gho sts. The donor N-(p-(2-benzoxazolyl)phenyl)-maleimide (BMI) and the ac ceptor fluram bind to SH- and NH2-residues, respectively. The fluoresc ence spectra and the time-dependent emission were consistent with radi ationless fluorescence energy transfer (RET). Band3 protein is the onl y membrane spanning protein with accessible SH-groups for the coupling of BMI molecules, and therefore only acceptor binding sites on the sa me band3 protein were counted by the RET measurements performed. A den sity of RET-effective acceptor binding sites c = 0.072 nm(-2) was calc ulated on the basis of the two-dimensional Forster-kinetics.