Study of the interaction between tosufloxacin tosylate and bovine serum albumin by multi-spectroscopic methods

Abstract

The interaction of tosufloxacin tosylate (TSFX) and bovine serum albumin (BSA) was studied by fluorescence spectroscopy, UV–vis spectroscopy and FT-IR spectroscopy. The results indicated that the intrinsic fluorescence of BSA was quenched by TSFX through a static quenching mechanism, and the effective binding constants ( K a ) were obtained by means of the modified Stern–Volmer equation. Thermodynamic parameters showed that electrostatic interaction was mostly responsible for the binding of TSFX to BSA. The binding distance ( r) between TSFX and Trp-212 was determined to be 3.90 nm according to Föster non-radiative energy transfer theory. BSA had a single class of binding site at Sudlow' site I in subdomain IIA for TSFX. The effects of TSFX on the conformation of BSA were analyzed by synchronous fluorescence spectra and three-dimensional fluorescence spectra, and the results exhibited that the hydrophobicity of tryptophan microenvironment was decreased. In FT-IR spectra, Fourier self-deconvolution, secondary derivative and the curve-fitting process were carried out to obtain the components of BSA secondary structure at 298 K and 310 K. The full basic data indicated that the presence of TSFX resulted in α -helix and β -sheet changing into β-turn and random, which displayed that TSFX induced the unfolding of the polypeptides of BSA.