The interaction of 5-(alkoxy)naphthalen-1-amine with bovine serum albumin and its effect on the conformation of protein.

The effects of binding and conformational changes induced by the neutral amphiphilic ligand [5-(alkoxy)naphthalen-1-amine] with different alkyl chain lengths on bovine serum albumin (BSA) have been studied using UV-visible and fluorescence spectroscopic methods. The BSA fluorescence exhibits appreciable bathochromic shift along with a reduction in fluorescence intensity and fluorescence lifetime upon binding with ligands. Ligand quenches the fluorescence of BSA in a concentration-dependent manner and deviates positively from the linear Stern-Volmer equation. The calculated quenching rate constants and binding constants were shown to depend entirely on the alkyl chain length of the ligands. After binding of probes with protein, the distance between the donor and acceptor was calculated using Forster theory. Ligands bind near Trp-134 in the subdomain IA of the native BSA and they become accessible to Trp-212 when BSA gets unfolded. The spectral data well supports the idea that BSA changes its three-dimensional conformation incrementally during its unfolding.