Fluorescence of spectrin-bound prodan.

A large blue-shift (delta lambda max = 87 nm) in the fluorescence emission maximum and 2-fold enhancement in the emission intensity of PRODAN in the presence of 1.5 microM dimeric spectrin from the same aqueous buffer was observed. Binding of PRODAN to spectrin was estimated from the concentration-dependent change in the ratio of two fluorescence intensities, I520nm for the unbound and I430nm corresponding to the spectrin-bound PRODAN. PRODAN binds to spectrin with a higher affinity (Kapp = 2 X 10(6)M-1) than those reported for BSA and tubulin (Kapp = 1 X 10(5)M-1 for BSA and 5 X 10(4)M-1 for tubulin). This is the first report of PRODAN binding at such a low protein concentration.