SELF-ASSOCIATION OF 8-ANILINO-1-NAPHTHALENE-SULFONATE MOLECULES - SPECTROSCOPIC CHARACTERIZATION AND APPLICATION TO THE INVESTIGATION OF PROTEIN-FOLDING

It was suggested long ago that the reason for the considerable increas e of 8-anilino-1-naphthalene-sulfonate (8-ANS) fluorescence intensity upon the transition from aqueous to organic solvents is the dissociati on of 8-ANS associates. To clarify this point the dependence of spectr al properties of the dye on concentration and solvent composition was investigated by means of steady-state and time-resolved fluorescence s pectroscopy. It was shown that the increase of 8-ANS concentration lea ds to the changes in the shape of absorption and fluorescence spectra of the dye, accompanied by the decrease in its fluorescence decay time values. Such changes were observed in aqueous and organic solvents fo r Mg2+- and NH4+-salts of 8-anilino-1-naphthalene-sulfonateic acid and reflect the existence of self-association of the dye molecules in bot h media. However, the decrease in fluorescence intensity induced by th e self-association of the probe molecules is too small to explain weak fluorescence of 8-ANS in water. At the same time, it expounds the dif ference between the decay times of protein-embedded 8-ANS molecules up on interaction of this probe with native and molten globule proteins. (C) 1998 Elsevier Science B,V. All rights reserved.