Probing the interaction of human serum albumin with vitamin B2 (riboflavin) and l-Arginine (l-Arg) using multi-spectroscopic, molecular modeling and zeta potential techniques

This study was designed to examine the interaction of Riboflavin (RB) and l-Arginine (l-Arg) with human serum albumin (HSA) using different spectroscopic, zeta potential and molecular modeling techniques under imitated physiological conditions. The resonance light scattering (RLS) method determined the critical aggregation concentration of RB on HSA in the presence and absence of l-Arg which confirmed the zeta potential results. The binding constants (Ka) of HSA–RB were 2.5×104 and 9.7×103 M−1, respectively in binary and ternary system at the excitation wavelength of 280 nm, also were 7.5×103 and 7.3×103, respectively in binary and ternary system at the excitation wavelength of 295 nm. Fluorescence spectroscopy demonstrated that in the presence of l-Arg, the binding constant of HSA–RB was increased. Static quenching was confirmed to results in the fluorescence quenching and FRET. The binding distances between HSA and RB in two- and three-component systems were estimated by the Forster theory which revealed that nonradiative energy transfer from HSA to RB occurred with a high probability. The effect of RB on the conformation of HSA was analyzed using synchronous fluorescence spectroscopy and circular dichroism (CD) in both systems. Docking studies demonstrated a reduction in the binding affinity between RB and HSA in the presence of l-Arg.