A spectroscopic study on the interaction between p-nitrophenol and bovine serum albumin

The interaction between p-nitrophenol (PNP) with bovine serum albumin (BSA) was investigated by fluorescence quenching, UV-visible absorption, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy under the simulative physiological conditions. It is found that PNP has a strong ability to quench the intrinsic fluorescence of BSA by forming a 1:1 ground-state complex with a binding constant of about 104 L mol−1. The values of the calculated thermodynamic parameters suggest that hydrogen bonds and hydrophobic forces played major roles in stabilizing the complex. The displacement experiments indicate that the binding of PNP to BSA primarily occurred in the sub-domain IIA (site I) of BSA. The binding distance r was calculated to be 1.58 nm based on the theory of Förster׳s non-radiation energy transfer. The analysis of synchronous fluorescence, FT-IR, CD, and three-dimensional fluorescence spectra reveals that the microenvironment of amino acid residues and the conformation of BSA were changed after addition of PNP.