Abstrat: Structural alteration of Urea-induced Bovine serum albumin and interaction of Oflxacin with urea-induced BSA were investigated by UV-vis and fluorescence spectroscopy .The results indicated that BSA followed a two-step, three-state transition with an intermediate in process of unfolding. With increasing the concentration of Urea, it can be found that the fluorescence of BSA decreased with early a blue shift of about 8 nm (from 344 nm to336 nm) and subsequently a red shift to 350 nm. When urea concentrations varied from 4.6 mol/L to 5.2 mol/L, oflx quenched fluorescence of intermediate of BSA with the optimal condition as fluorescence quenching constants (KQ=10.46×104 L/mol，Urea 4.8 mol/L) and binding constants (KA=3.8807×105 L/mol，Urea 4.8 mol/L), whereas with small binding sites（n=0.76，Urea 5.0 mol/L）and low energy transfer efficiency（E=0.3002, Urea 4.8 mol/L）. Synchronous fluorescence spectrometry showed that during unfolding of BSA induced by urea, Trp-212 residue microenvironment has no changes, at the same time the maximal fluorescence peak of Tyr shift towards short-wavelength. The introduction of Oflx indued Trp microenvironment to more hydrophodic. And it also accelerated the denaturation of BSA by urea.

Key words: Urea, Oflxacin, Bovine Serum Albumin, Fluorescence quenching, Synchronous fluorescence