Nanosecond decay studies of a fluorescence probe bound to apomyoglobin

Excited state interactions of N-(p-tolyl)-2-aminonaphthalene-6-sulfonate (2, 6 p-TNS) bound to apomyoglobin were studied by nanosecond time-resolved emission spectroscopy. A dynamic interaction of the excited dye molecule with its binding site, associated with a significant change in the emission energy with time, was observed. The decay kinetics were found to be complex and consistent with the kinetic model for solvent relaxation as proposed by Bakhshiev et al. (Opt. Spectrosc. 21:307. 1966). The behavior of 2, 6 p-TNS bound to apomyoglobin was found to be qualitatively similar to that of the dye dissolved in a viscous solvent such as glycerol or adsorbed to egg lecithin vesicles. The detailed information obtained by following the changes in emission spectra of fluorescent probes on the nanosecond time scale leads to a better understanding of their interactions with biological systems.