Denaturation study of bovine serum albumin induced by the urea by fluorescence spectroscopy

In this paper,the interaction between urea and bovine serum albumin(BSA)in aqueous solution as well as the denaturation process of BSA were studied by using fluorescence spectroscopy technique at 30℃ and three pHs.The fluorescence spectroscopic data have been analysed by using the methods described by Pace.The unfolded fraction(fu),the denaturation equilibrium constant(Ku)and the free energy of unfolding(△Gu)of protein have been calculated.Then,the transition midpoint(D1/2)and the steepness of the transition region(m)and the free energy of unfolding(ΔGH2O)were obtained.The results which were obtained by thermodynamic analysis indicated that the denaturation of BSA induced by urea is through direct and indirect effects,the interaction between urea and BSA is divided into three stages:the first stage is at the urea concentration below 4 mol·L-1.In this stage,the direct interaction between urea and BSA is the main interaction,while the direct interaction is stronger under acidulous condition.The second stage is in the urea concentrations from 4 mol·L-1 to 6 mol·L-1.In this stage,the structure of the water around the BSA is changed by the interaction of urea and solvent water.BSA structure becomes more closely,that is protein stiffening.The third stage is at the urea concentrations higher than 6 mol·L-1.In this stage,urea molecules combine with the exposed groups.At the urea concentrations is 8mol·L-1,the unfolded fractionfuabout 1,the denaturation of bovine serum albumin induced by urea completely.