Investigation on the interactions of silymarin to bovine serum albumin and lysozyme by fluorescence and absorbance

The interactions of silymarin with bovine serum albumin (BSA) and lysozyme (LYS) were investigated in physiological buffer (pH = 7.4) by fluorescence spectroscopy and UV–vis absorption spectroscopy. The mechanism study indicated that silymarin could strongly quench the intrinsic fluorescence of BSA and LYS through static quenching procedures. At 291 K, the values of the binding constant K_A were 4.20×10⁴ and 4.71×10⁴ L mol^?1 for silymarin–BSA and silymarin–LYS, respectively. Using thermodynamic equations, the conclusion that hydrophobic and electrostatic forces played an important role in stabilizing complex of silymarin–BSA or silymarin–LYS was obtained. The effects of Cu²⁺, Mg²⁺, Ca²⁺, Fe²⁺, and Fe³⁺ on the binding were also studied at 291 K. According to Förster’s nonradiative energy transfer theory, the distances r₀ between donor and acceptor were calculated to be 3.36 and 2.71 nm for silymarin–BSA and silymarin–LYS, respectively. Synchronous fluorescence spectra showed that the conformation of BSA and LYS were changed by silymarin.