Study of the interaction between mercury (II) and bovine serum albumin by spectroscopic methods

• BSA-fluorescence quenching was a result of the formation of mercury (II) -BSA complex.
• The interaction between BSA and mercury (II) were mainly enthalpy-driven.There was a single class of binding site on the BSA for mercury (II).
• The energy transfer from BSA to mercury (II) occurred with high possibility.
• Mercury (II) resulted in some micro-environmental and conformational changes of BSA molecules. 

Mercury is a significant environmental pollutant that originates from industry. Mercury will bind with albumin and destroy biological functions in humans if it enters the blood. In this paper, the interaction between mercury (II) and bovine serum albumin (BSA) was investigated in vitro by fluorescence, UV–Vis absorption and circular dichroism (CD) under simulated physiological conditions. This study proves that the probable quenching mechanism of BSA by mercury (II) was mainly static quenching due to the formation of a mercury (II)–BSA complex. The quenching constant Ka and the corresponding thermodynamic parameters (ΔH, ΔS and ΔG) at four different temperatures were calculated by a modified Stern–Volmer equation and the van’t Hoff equation, respectively. The results revealed that the interaction between mercury (II) and BSA was mainly enthalpy-driven and that hydrogen bonding and van der Waals forces played a major role in the reaction. The obtained data for binding sites of n approximately equal to 1 indicated that there was a single class of binding site for the BSA with mercury (II). The value of the distance r (3.55 nm), determined by Föster's non-radioactive energy transfer theory, suggested that the energy transfer from BSA to mercury (II) occurred with a high probability. The conformational investigation from synchronous fluorescence, CD spectroscopy and three-dimensional fluorescence showed that the presence of mercury (II) resulted in micro-environmental and conformational changes of the BSA molecules, which may be responsible for the toxicity of mercury (II) in vivo.