Interaction of the nonionic surfactant Hecamegs with the plasma protein Bovine Serum Albumin (BSA), and its effect on protein conformation,has been studied using spectroscopic techniques such as steady-state and time-resolved fluorescence and circular dichroism. A weak interaction of the surfactant with BSA is reflected by changes in the intrinsic fluorescence of BSA in either steady-state or time-resolved measurements. The fluorescence intensity data allowed us to determine the corresponding binding curve, which suggests a sequential binding mechanism, in which the surfactant first occupies the hydrophobic sites of the inner protein cavity and then,condenses onto the surface hydrophobicsites of BSA via a cooperative mechanism.Additional fluorescence data obtained by synchronous,three-dimensional and anisotropy experiments show that the surfactant mainly interacts with the tryptophan residues of BSA,which seem to experience motional restriction as a result of this interaction.Time-resolved fluorescence data,which were analyzed using the modified Stern–Volmer equation,also support the above mechanism.Finally,far-UV circular dichroism studies indicated that the secondary structure of the protein remains almost unaltered even for BSA to surfactant molar ratio as high as 1 to100.
