Probing the Binding of Rifampicin to Bovine Serum Albumin in Aqueous Solution

The binding of rifampicin (RFP), an anti-tuberculosis agent, to bovine serum albumin (BSA) was studied at physiological conditions (pH=7.40) by a spectroscopic approach. In the discussion of the quenching mechanism, it was proved that the fluorescence quenching of BSA by RFP is a result of the formation of a RFP–BSA complex. Binding parameters were determined using the modified Stern-Volmer equation and Scatchard’s equation to provide a measure of the binding affinity between RFP and BSA. The resulting thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures indicate that electrostatic interactions play a major role in RFP–BSA association. Site marker competitive displacement experiments demonstrate that RFP binds with high affinity to the site I (subdomain IIA) of BSA. Furthermore, the effect of metal ions on the RFP–BSA system was studied, and the specific binding distance r (3.38 nm) between donor and acceptor (RFP) was obtained according to the fluorescence resonance energy transfer (FRET).