The aim of this work was to study the interaction of sulpiride with human serum albumin (HSA) and bovine serum albumin (BSA) through the fluorescence quenching technique. As sulpiride molecules emit fluorescence, we have developed a simple mathematical model to discriminate the quencher fluorescence from the albumin fluorescence in the solution where they interact. Sulpiride is an antipsychotic used in the treatment of several psychiatric disorders. We selectively excited the fluorescence of tryptophan residues with 290 nm wavelength and observed the quenching by titrating HSA and BSA solutions with sulpiride. Stern-Volmer graphs were plotted and quenching constants were estimated. Results showed that sulpiride form complexes with both albumins. Estimated association constants for the interaction sulpiride-HSA were 2.20 (±0.08) × 10⁴ M(-1), at 37 °C, and 5.46 (±0.20) × 10⁴ M(-1), at 25 °C. Those for the interaction sulpiride-BSA are 0.44 (±0.01) × 10⁴ M(-1), at 37 °C and 2.17 (±0.04) × 10⁴ M(-1), at 25 °C. The quenching intensity of BSA, which contains two tryptophan residues in the peptide chain, was found to be higher than that of HSA, what suggests that the primary binding site for sulpiride in albumin should be located next to the sub domain IB of the protein structure.
Keywords: albumins; fluorescence quenching; interaction; sulpiride.