Investigation of the interaction between bromocriptine and human serum albumin with spectroscopic techniques and computational approaches.

Fluorescence and absorption spectroscopy coupled with molecular docking techniques were chosen to reveal the molecular relationship between bromocriptine (BRC), a dopamine agonist, and human serum albumin (HSA), the major carrier protein in the bloodstream. The gradual decrease of Stern-Volmer constant (K_SV) with increasing temperatures noted that BRC induced quenching in HSA fluorescence occurred via a static quenching mechanism, thus indicating the formation of complexes between BRC and HSA. The changes observed in the UV-vis absorption spectra of HSA as a result of BRC addition and the fact that the biomolecular quenching rate constants (K_q) calculated for the BRC-HSA interaction are significantly larger than the highest value of the dynamic quenching rate constant also support this conclusion. Considering the experimentally obtained binding constant (K_a) values ​​(2.6 - 3.8 x 10⁴ M^-1), BRC appeared to bind to HSA with a moderate affinity. Analysis of thermodynamic data suggested the association of hydrophobic interactions, H-bonds and van der Waals forces as the main interaction forces in the BRC-HSA binding. It was determined by 3-D fluorescence spectra that the binding of BRC to the protein led to significant changes in the Tyr/Trp microenvironment of the protein. Docking analyses and drug displacement experiments identified that BRC likely binds to subdomain IIA (Site I) of HSA.